Glossary

  • α-helix
    Type of secondary structure of proteins formed by folding of the polypeptide into a helix shape with hydrogen bonds stabilizing the structure
  • β-pleated
    Secondary structure found in proteins in which “pleats” are formed by hydrogen bonding between atoms on the backbone of the polypeptide chain
  • Absorption spectrum
    Range of wavelengths of electromagnetic radiation absorbed by a given substance
  • Acetyl CoA
    Combination of an acetyl group derived from pyruvic acid and coenzyme A, which is made from pantothenic acid (a B-group vitamin)
  • Acquired characteristics
    Modifications caused by an individual’s environment that can be inherited by its offspring
  • Activation energy
    Energy necessary for reactions to occur
  • Active site
    Specific region of the enzyme to which the substrate binds
  • Active transport
    Method of transporting material that requires energy
  • Adaptation
    Heritable trait or behavior in an organism that aids in its survival and reproduction in its present environment
  • Adaptive evolution
    Increase in frequency of beneficial alleles and decrease in deleterious alleles due to selection
  • Adaptive radiation
    Speciation when one species radiates out to form several other species
  • Aerobic respiration
    Process in which organisms convert energy in the presence of oxygen
  • Alimentary canal
    Tubular digestive system with a mouth and anus
  • Aliphatic hydrocarbon
    Hydrocarbon consisting of a linear chain of carbon atoms
  • Allele
    Gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes
  • Allele frequency
    Rate at which a specific allele appears within a population
  • Allopatric speciation
    Speciation that occurs via geographic separation
  • Allopolyploid
    Polyploidy formed between two related, but separate species
  • Allosteric inhibition
    Inhibition by a binding event at a site different from the active site, which induces a conformational change and reduces the affinity of the enzyme for its substrate
  • Alpha-helix
    Type of secondary structure of proteins formed by folding of the polypeptide into a helix shape with hydrogen bonds stabilizing the structure
  • Alternation of generations
    Life-cycle type in which the diploid and haploid stages alternate
  • Amino acid
    Monomer of a protein; has a central carbon or alpha carbon to which an amino group, a carboxyl group, a hydrogen, and an R group or side chain is attached; the R group is different for the most common 20 amino acids
  • Aminopeptidase
    Protease that breaks down peptides to single amino acids; secreted by the brush border of small intestine
  • Amphiphilic
    Molecule possessing a polar or charged area and a nonpolar or uncharged area capable of interacting with both hydrophilic and hydrophobic environments
  • Anabolic
    (also, anabolism) Pathways that require an input of energy to synthesize complex molecules from simpler ones
  • Anaerobic
    Process that does not use oxygen
  • Anaerobic cellular respiration
    Process in which organisms convert energy for their use in the absence of oxygen
  • Anaphase
    Stage of mitosis during which sister chromatids are separated from each other
  • Aneuploid
    Individual with an error in chromosome number; includes deletions and duplications of chromosome segments
  • Aneuploidy
    Condition of a cell having an extra chromosome or missing a chromosome for its species
  • Anion
    Negative ion that is formed by an atom gaining one or more electrons
  • Antenna protein
    Pigment molecule that directly absorbs light and transfers the energy absorbed to other pigment molecules
  • Antibiotic resistance
    Ability of an organism to be unaffected by the actions of an antibiotic
  • Antiporter
    Transporter that carries two ions or small molecules in different directions
  • Anus
    Exit point for waste material
  • Apoptosis
    Programmed cell death
  • Aquaporin
    Channel protein that allows water through the membrane at a very high rate
  • Assortative mating
    When individuals tend to mate with those who are phenotypically similar to themselves
  • Atomic mass
    Calculated mean of the mass number for an element’s isotopes
  • Atomic number
    Total number of protons in an atom
  • ATP
    adenosine triphosphate, the cell’s energy currency
  • ATP synthase
    Membrane-embedded protein complex that adds a phosphate to ADP with energy from protons diffusing through it
  • Autocrine signal
    Signal that is sent and received by the same or similar nearby cells
  • Autoinducer
    Signaling molecule secreted by bacteria to communicate with other bacteria of its kind and others
  • Autopolyploid
    Polyploidy formed within a single species
  • Autosome
    Any of the non-sex chromosomes
  • Autosomes
    Any of the non-sex chromosomes
  • Balanced chemical equation
    Statement of a chemical reaction with the number of each type of atom equalized for both the products and reactants
  • Behavioral isolation
    Type of reproductive isolation that occurs when a specific behavior or lack of one prevents reproduction from taking place
  • beta-pleated sheet
    Secondary structure found in proteins in which “pleats” are formed by hydrogen bonding between atoms on the backbone of the polypeptide chain
  • Bile
    Digestive juice produced by the liver; important for digestion of lipids
  • Binary fission
    Prokaryotic cell division process
  • Bioenergetics
    Study of energy flowing through living systems
  • Biomarker
    Individual protein that is uniquely produced in a diseased state
  • Biotechnology
    Use of biological agents for technological advancement
  • Blending theory of inheritance
    Hypothetical inheritance pattern in which parental traits are blended together in the offspring to produce an intermediate physical appearance
  • Bolus
    Mass of food resulting from chewing action and wetting by saliva
  • Bottleneck effect
    Magnification of genetic drift as a result of natural events or catastrophes
  • Buffer
    Substance that prevents a change in pH by absorbing or releasing hydrogen or hydroxide ions
  • Calvin cycle
    Light-independent reactions of photosynthesis that convert carbon dioxide from the atmosphere into carbohydrates using the energy and reducing power of ATP and NADPH
  • cAMP
    Second messenger that is derived from ATP
  • Carbohydrate
    Biological macromolecule in which the ratio of carbon to hydrogen and to oxygen is 1:2:1; carbohydrates serve as energy sources and structural support in cells and form the a cellular exoskeleton of arthropods
  • Carbon fixation
    Process of converting inorganic CO2 gas into organic compounds
  • Carboxypeptidase
    Protease that breaks down peptides to single amino acids; secreted by the brush border of the small intestine
  • Carnivore
    Animal that consumes animal flesh
  • Carotenoid
    Photosynthetic pigment that functions to dispose of excess energy
  • Carrier protein
    Membrane protein that moves a substance across the plasma membrane by changing its own shape
  • Catabolic
    (also, catabolism) Pathways in which complex molecules are broken down into simpler ones
  • Cation
    Positive ion that is formed by an atom losing one or more electrons
  • Caveolin
    Protein that coats the cytoplasmic side of the plasma membrane and participates in the process of liquid uptake by potocytosis
  • cDNA library
    Collection of cloned cDNA sequences
  • Cell cycle
    Ordered series of events involving cell growth and cell division that produces two new daughter cells
  • Cell cycle checkpoint
    Mechanism that monitors the preparedness of a eukaryotic cell to advance through the various cell cycle stages
  • Cell plate
    Structure formed during plant cell cytokinesis by Golgi vesicles, forming a temporary structure (phragmoplast) and fusing at the metaphase plate; ultimately leads to the formation of cell walls that separate the two daughter cells
  • Cell-surface receptor
    Cell-surface protein that transmits a signal from the exterior of the cell to the interior, even though the ligand does not enter the cell
  • Cellular cloning
    Production of identical cell populations by binary fission
  • Cellulose
    Polysaccharide that makes up the cell wall of plants; provides structural support to the cell
  • Centimorgan
    Relative distance that corresponds to a recombination frequency of 0.01
  • Central vacuole
    large plant cell organelle that regulates the cell’s storage compartment, holds water, and plays a significant role in cell growth as the site of macromolecule degradation
  • Centriole
    Rod-like structure constructed of microtubules at the center of each animal cell centrosome
  • Centromere
    Region at which sister chromatids are bound together; a constricted area in condensed chromosomes
  • Centrosome
    Region in animal cells made of two centrioles
  • Cephalic phase
    First phase of digestion, controlled by the neural response to the stimulus provided by food
  • Chain termination method
    Method of DNA sequencing using labeled dideoxynucleotides to terminate DNA replication; it is also called the dideoxy method or the Sanger method
  • Channel protein
    Membrane protein that allows a substance to pass through its hollow core across the plasma membrane
  • Chaperone
    (also, chaperonin) protein that helps nascent protein in the folding process
  • Chemical bond
    Interaction between two or more of the same or different atoms that results in the formation of molecules
  • Chemical energy
    Energy potential energy in chemical bonds that is released when those bonds are broken
  • Chemical reaction
    Process leading to the rearrangement of atoms in molecules
  • Chemical reactivity
    The ability to combine and to chemically bond with each other
  • Chemical synapse
    Small space between axon terminals and dendrites of nerve cells where neurotransmitters function
  • Chemiosmosis
    Process in which there is a production of adenosine triphosphate (ATP) in cellular metabolism by the involvement of a proton gradient across a membrane
  • Chemoautotroph
    Organism that can build organic molecules using energy derived from inorganic chemicals instead of sunlight
  • Chiasma
    (plural, chiasmata) The structure that forms at the crossover points after genetic material is exchanged
  • Chiasmata
    (singular, chiasma) The structure that forms at the crossover points after genetic material is exchanged
  • Chitin
    Type of carbohydrate that forms the outer skeleton of all arthropods that include crustaceans and insects, it also forms the cell wall of fungi.
  • Chlorophyll
    Green pigment that captures the light energy that drives the light reactions of photosynthesis
  • Chlorophyll a
    Form of chlorophyll that absorbs violet-blue and red light and consequently has a bluish-green color; the only pigment molecule that performs the photochemistry by getting excited and losing an electron to the electron transport chain
  • Chlorophyll b
    Accessory pigment that absorbs blue and red-orange light and consequently has a yellowish-green tint
  • Chloroplast
    Organelle in which photosynthesis takes place
  • Cholecystokinin
    Hormone that stimulates the contraction of the gallbladder to release bile
  • Chromatid
    Single DNA molecule of two strands of duplicated DNA and associated proteins held together at the centromere
  • Chromatin
    Protein-DNA complex that serves as the building material of chromosomes
  • Chromosomal Theory of Inheritance
    Theory proposing that chromosomes are the vehicles of genes and that their behavior during meiosis is the physical basis of the inheritance patterns that Mendel observed
  • Chromosome
    Structure within the nucleus that is made up of chromatin that contains DNA, the hereditary material
  • Chromosome inversion
    Detachment, 180° rotation, and reinsertion of a chromosome arm
  • Chylomicron
    Small lipid globule
  • Chyme
    Mixture of partially digested food and stomach juices
  • Chymotrypsin
    Pancreatic protease
  • Cilium
    (plural = cilia) short, hair-like structure that extends from the plasma membrane in large numbers and is used to move an entire cell or move substances along the outer surface of the cell
  • Citric acid cycle
    Alternate name for the citric acid cycle, named after the group name for citric acid, tricarboxylic acid (TCA)
  • Clathrin
    Protein that coats the inward-facing surface of the plasma membrane and assists in the formation of specialized structures, like coated pits, for phagocytosis
  • Cleavage furrow
    Constriction formed by an actin ring during cytokinesis in animal cells that leads to cytoplasmic division
  • Cline
    Gradual geographic variation across an ecological gradient
  • Clone
    Exact replica
  • Codominance
    In a heterozygote, complete and simultaneous expression of both alleles for the same characteristic
  • Coenzyme
    Small organic molecule, such as a vitamin or its derivative, which is required to enhance the activity of an enzyme
  • Cofactor
    Cofactor inorganic ion, such as iron and magnesium ions, required for optimal regulation of enzyme activity
  • Cohesin
    Proteins that form a complex that seals sister chromatids together at their centromeres until anaphase II of meiosis
  • Competitive inhibition
    Type of inhibition in which the inhibitor competes with the substrate molecule by binding to the active site of the enzyme
  • Concentration gradient
    Area of high concentration adjacent to an area of low concentration
  • Condensin
    Proteins that help sister chromatids coil during prophase
  • Contig
    Larger sequence of DNA assembled from overlapping shorter sequences
  • Continuous variation
    Inheritance pattern in which a character shows a range of trait values with small gradations rather than large gaps between them
  • Convergent evolution
    Process by which groups of organisms independently evolve to similar forms
  • Covalent bond
    Type of strong bond formed between two atoms of the same or different elements; forms when electrons are shared between atoms
  • Crossover
    Exchange of genetic material between non-sister chromatids resulting in chromosomes that incorporate genes from both parents of the organism
  • Cyclic AMP
    Second messenger that is derived from ATP
  • Cyclic AMP-dependent kinase
    Kinase that is activated by binding to cAMP
  • Cyclin
    One of a group of proteins that act in conjunction with cyclin-dependent kinases to help regulate the cell cycle by phosphorylating key proteins; the concentrations of cyclins fluctuate throughout the cell cycle
  • Cyclin-dependent kinase
    One of a group of protein kinases that helps to regulate the cell cycle when bound to cyclin; it functions to phosphorylate other proteins that are either activated or inactivated by phosphorylation
  • Cytochrome complex
    Group of reversibly oxidizable and reducible proteins that forms part of the electron transport chain between photosystem II and photosystem I
  • Cytogenetic mapping
    Technique that uses a microscope to create a map from stained chromosomes
  • Cytokinesis
    Division of the cytoplasm following mitosis that forms two daughter cells.
  • Cytoplasm
    Entire region between the plasma membrane and the nuclear envelope, consisting of organelles suspended in the gel-like cytosol, the cytoskeleton, and various chemicals
  • Cytoskeleton
    Network of protein fibers that collectively maintain the shape of the cell, secure some organelles in specific positions, allow cytoplasm and vesicles to move within the cell, and enable unicellular organisms to move independently
  • Cytosol
    Gel-like material of the cytoplasm in which cell structures are suspended
  • DAG
    Cleavage product of PIP2 that is used for signaling within the plasma membrane
  • Darwinian fitness
    Individual’s ability to survive and reproduce
  • Dehydration
    (also, condensation) reaction that links monomer molecules together, releasing a molecule of water for each bond formed
  • Denaturation
    Loss of shape in a protein as a result of changes in temperature, pH, or exposure to chemicals
  • Denature
    Process that changes the natural properties of a substance
  • Deoxynucleotide
    Individual monomer (single unit) of DNA
  • Dephosphorylation
    Removal of a phosphate group from a molecule
  • Desmosome
    Linkage between adjacent epithelial cells that forms when cadherins in the plasma membrane attach to intermediate filaments
  • Diacylglycerol
    Cleavage product of PIP2 that is used for signaling within the plasma membrane
  • Dideoxynucleotide
    Individual monomer of DNA that is missing a hydroxyl group (–OH)
  • Diffusion
    Passive process of transport of low-molecular weight material according to its concentration gradient
  • Digestion
    Mechanical and chemical break down of food into small organic fragments
  • Dihybrid
    Result of a cross between two true-breeding parents that express different traits for two characteristics
  • Dimer
    Chemical compound formed when two molecules join together
  • Dimerization
    Interaction of two receptor proteins to form a functional complex called a dimer
  • Dipeptidase
    Protease that breaks down peptides to single amino acids; secreted by the brush border of small intestine
  • Diploid
    Cell, nucleus, or organism containing two sets of chromosomes (2n)
  • Diploid-dominant
    Life-cycle type in which the multicellular diploid stage is prevalent
  • Directional selection
    Selection that favors phenotypes at one end of the spectrum of existing variation
  • Disaccharide
    Two sugar monomers that are linked together by a glycosidic bond
  • Discontinuous variation
    Inheritance pattern in which traits are distinct and are transmitted independently of one another
  • Dispersal
    Allopatric speciation that occurs when a few members of a species move to a new geographical area
  • Divergent evolution
    Process by which groups of organisms evolve in diverse directions from a common point
  • Diversifying selection
    Selection that favors two or more distinct phenotypes
  • DNA
    Deoxyribonucleic acid. Double-helical molecule that carries the hereditary information of the cell
  • DNA microarray
    Method used to detect gene expression by analyzing an array of DNA fragments that are fixed to a glass slide or a silicon chip to identify active genes and identify sequences
  • Dominant
    Trait which confers the same physical appearance whether an individual has two copies of the trait or one copy of the dominant trait and one copy of the recessive trait
  • Dominant lethal
    Inheritance pattern in which an allele is lethal both in the homozygote and the heterozygote; this allele can only be transmitted if the lethality phenotype occurs after reproductive age
  • Duodenum
    First part of the small intestine where a large part of digestion of carbohydrates and fats occurs
  • Elastase
    Pancreatic protease
  • Electrochemical gradient
    Gradient produced by the combined forces of an electrical gradient and a chemical gradient
  • Electrogenic pump
    Pump that creates a charge imbalance
  • Electrolyte
    Ion necessary for nerve impulse conduction, muscle contractions and water balance
  • Electromagnetic spectrum
    Range of all possible frequencies of radiation
  • Electron
    Negatively charged subatomic particle that resides outside of the nucleus in the electron orbital; lacks functional mass and has a negative charge of –1 unit
  • Electron configuration
    arrangement of electrons in an atom’s electron shell (for example, 1s2 2s2 2p6)
  • Electron microscope
    an instrument that magnifies an object using a beam of electrons passed and bent through a lens system to visualize a specimen
  • Electron orbital
    How electrons are spatially distributed surrounding the nucleus; the area where an electron is most likely to be found
  • Electron transport chain
    Group of proteins between PSII and PSI that pass energized electrons and use the energy released by the electrons to move hydrogen ions against their concentration gradient into the thylakoid lumen
  • Electronegativity
    The ability of some elements to attract electrons (often of hydrogen atoms), acquiring partial negative charges in molecules and creating partial positive charges on the hydrogen atoms
  • Electrophoresis
    Technique used to separate DNA fragments according to size
  • Enantiomers
    Molecules that share overall structure and bonding patterns, but differ in how the atoms are three dimensionally placed such that they are mirror images of each other
  • Endergonic
    Describes chemical reactions that require energy input
  • Endocrine cell
    Cell that releases ligands involved in endocrine signaling (hormones)
  • Endocrine signal
    Long-distance signal that is delivered by ligands (hormones) traveling through an organism's circulatory system from the signaling cell to the target cell
  • Endocrine system
    System that controls the response of the various glands in the body and the release of hormones at the appropriate times
  • Endocytosis
    Type of active transport that moves substances, including fluids and particles, into a cell
  • Endomembrane system
    group of organelles and membranes in eukaryotic cells that work together modifying, packaging, and transporting lipids and proteins
  • Endoplasmic reticulum
    series of interconnected membranous structures within eukaryotic cells that collectively modify proteins and synthesize lipids
  • Enthalpy
    Total energy of a system
  • Entropy
    Measure of randomness or disorder within a system
  • Enzyme-linked receptor
    Cell-surface receptor with intracellular domains that are associated with membrane-bound enzymes
  • Epistasis
    Antagonistic interaction between genes such that one gene masks or interferes with the expression of another
  • Equilibrium
    Steady-state of relative reactant and product concentration in reversible chemical reactions in a closed system
  • Esophagus
    Tubular organ that connects the mouth to the stomach
  • Essential nutrient
    Nutrient that cannot be synthesized by the body; it must be obtained from food
  • EST
    Short STS that is identified with cDNA
  • Eukaryote
    Organism with cells that have nuclei and membrane-bound organelles
  • Eukaryotic cell
    Cell that has a membrane-bound nucleus and several other membrane-bound compartments or sacs
  • Euploid
    Individual with the appropriate number of chromosomes for their species
  • Evolution
    Process of gradual change during which new species arise from older species and some species become extinct
  • Evolutionary fitness
    Individual’s ability to survive and reproduce
  • Exergonic
    Describes chemical reactions that release free energy
  • Exocytosis
    Process of passing bulk material out of a cell
  • Expressed sequence tag
    Short STS that is identified with cDNA
  • Extracellular domain
    Region of a cell-surface receptor that is located on the cell surface
  • Extracellular matrix
    material (primarily collagen, glycoproteins, and proteoglycans) secreted from animal cells that provides mechanical protection and anchoring for the cells in the tissue
  • F1F0 ATP synthase
    Membrane-embedded protein complex that adds a phosphate to ADP with energy from protons diffusing through it
  • Facilitated transport
    Process by which material moves down a concentration gradient (from high to low concentration) using integral membrane proteins
  • False negative
    Incorrect test result that should have been positive
  • Feedback inhibition
    Effect of a product of a reaction sequence to decrease its further production by inhibiting the activity of the first enzyme in the pathway that produces it
  • Fertilization
    Union of two haploid cells from two individual organisms
  • First gap
    First phase of interphase centered on cell growth during mitosis
  • Fitness
    Measure of successful reproduction, the passing on alleles to the next generation
  • Flagellum
    (plural = flagella) long, hair-like structure that extends from the plasma membrane and is used to move the cell
  • Fluid mosaic model
    Describes the structure of the plasma membrane as a mosaic of components including phospholipids, cholesterol, proteins, glycoproteins, and glycolipids (sugar chains attached to proteins or lipids, respectively), resulting in a fluid character (fluidity)
  • Foreign DNA
    DNA that belongs to a different species or DNA that is artificially synthesized
  • Founder effect
    Event that initiates an allele frequency change in part of the population, which is not typical of the original population
  • Free energy
    Gibbs free energy is the usable energy, or energy that is available to do work
  • Frequency-dependent selection
    Selection that favors phenotypes that are either common (positive frequency- dependent selection) or rare (negative frequency-dependent selection)
  • FtsZ
    Tubulin-like protein component of the prokaryotic cytoskeleton that is important in prokaryotic cytokinesis (name origin: Filamenting temperature-sensitive mutant Z)
  • G-protein-linked receptor
    Cell-surface receptor that activates membrane-bound G-proteins to transmit a signal from the receptor to nearby membrane components
  • G0 phase
    Distinct from the G1 phase of interphase; a cell in G0 is not preparing to divide
  • G1 phase
    First phase of interphase centered on cell growth during mitosis
  • G2 phase
    Third phase of interphase during which the cell undergoes final preparations for mitosis
  • Gallbladder
    Organ that stores and concentrates bile
  • Gamete
    Haploid reproductive cell or sex cell (sperm, pollen grain, or egg)
  • Gametic barrier
    Prezygotic barrier occurring when closely related individuals of different species mate, but differences in their gamete cells (eggs and sperm) prevent fertilization from taking place
  • Gametophyte
    A multicellular haploid life-cycle stage that produces gametes
  • Gap junction
    Channel between two adjacent animal cells that allows ions, nutrients, and low molecular weight substances to pass between cells, enabling the cells to communicate
  • Gastric inhibitory peptide
    Hormone secreted by the small intestine in the presence of fatty acids and sugars; it also inhibits acid production and peristalsis in order to slow down the rate at which food enters the small intestine
  • Gastric phase
    Digestive phase beginning once food enters the stomach; gastric acids and enzymes process the ingested materials
  • Gastrin
    Hormone which stimulates hydrochloric acid secretion in the stomach
  • Gastrovascular cavity
    Digestive system consisting of a single opening
  • Gel electrophoresis
    Technique used to separate molecules on the basis of size using electric charge
  • Gene
    Physical and functional unit of heredity, a sequence of DNA that codes for a protein.
  • Gene flow
    Flow of alleles in and out of a population due to the migration of individuals or gametes
  • Gene frequency
    Rate at which a specific allele appears within a population
  • Gene pool
    All of the alleles carried by all of the individuals in the population
  • Gene targeting
    Method for altering the sequence of a specific gene by introducing the modified version on a vector
  • Gene therapy
    Technique used to cure inheritable diseases by replacing mutant genes with good genes
  • Genetic diagnosis
    Diagnosis of the potential for disease development by analyzing disease-causing genes
  • Genetic drift
    Effect of chance on a population’s gene pool
  • Genetic engineering
    Alteration of the genetic makeup of an organism
  • Genetic map
    Outline of genes and their location on a chromosome
  • Genetic marker
    Gene or sequence on a chromosome with a known location that is associated with a specific trait
  • Genetic recombination
    Exchange of DNA between homologous pairs of chromosomes
  • Genetic structure
    Distribution of the different possible genotypes in a population
  • Genetic testing
    Process of testing for the presence of disease-causing genes
  • Genetic variance
    Diversity of alleles and genotypes in a population
  • Genetically modified organism
    Organism whose genome has been artificially changed
  • Genome
    Total genetic information of a cell or organism
  • Genome annotation
    Process of attaching biological information to gene sequences
  • Genome mapping
    Process of finding the location of genes on each chromosome
  • Genomic library
    Collection of cloned DNA which represents all of the sequences and fragments from a genome
  • Genomics
    Study of entire genomes including the complete set of genes, their nucleotide sequence and organization, and their interactions within a species and with other species
  • Genotype
    Underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism
  • Genotype frequency
    The proportion of a specific genotype in a population relative to all other genotypes for those genes that are present in the population
  • Geographical variation
    Differences in the phenotypic variation between populations that are separated geographically
  • Germ cells
    Specialized cell line that produces gametes, such as eggs or sperm
  • Gizzard
    Muscular organ that grinds food
  • GLUT protein
    Integral membrane protein that transports glucose
  • Glycogen
    Storage carbohydrate in animals
  • Glycolipid
    Combination of carbohydrates and lipids
  • Glycolysis
    Process of breaking glucose into two three-carbon molecules with the production of ATP and NADH
  • Glycoprotein
    Combination of carbohydrates and proteins
  • Glycosidic bond
    A bond formed by a dehydration reaction between two monosaccharides with the elimination of a water molecule
  • GMO
    Organism whose genome has been artificially changed
  • Golgi apparatus
    Eukaryotic organelle made up of a series of stacked membranes that sorts, tags, and packages lipids and proteins for distribution
  • Good genes hypothesis
    Theory of sexual selection that argues individuals develop impressive ornaments to show off their efficient metabolism or ability to fight disease
  • Gradual speciation model
    Model that shows how species diverge gradually over time in small steps
  • Granum
    Stack of thylakoids located inside a chloroplast
  • Growth factor
    Ligand that binds to cell-surface receptors and stimulates cell growth
  • Habitat isolation
    Reproductive isolation resulting when populations of a species move or are moved to a new habitat, taking up residence in a place that no longer overlaps with the other populations of the same species
  • Handicap principle
    Theory of sexual selection that argues only the fittest individuals can afford costly traits
  • Haploid
    Cell, nucleus, or organism containing one set of chromosomes (n)
  • Haploid-dominant
    Life-cycle type in which the multicellular haploid stage is prevalent
  • Hardy–Weinberg principle of equilibrium
    A stable, non-evolving state of a population in which allelic frequencies are stable over time
  • Heat
    Energy transferred from one system to another that does not work (energy of the motion of molecules or particles)
  • Heat energy
    Total bond energy of reactants or products in a chemical reaction
  • Heat of vaporization
    High amount of energy required for liquid water to turn into water vapor
  • Helicase
    During replication, this enzyme helps to open up the DNA helix by breaking the hydrogen bonds
  • Hemizygous
    Presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant
  • Herbivore
    Animal that consumes strictly plant diet
  • Heritability
    Fraction of population variation that can be attributed to its genetic variance
  • Heterotroph
    Organism that consumes organic substances or other organisms for food
  • Heterozygous
    Having two different alleles for a given gene on the homologous chromosome
  • Histone
    One of several similar, highly conserved, low molecular weight, basic proteins found in the chromatin of all eukaryotic cells; associates with DNA to form nucleosomes
  • Homeostasis
    Ability of an organism to maintain constant internal conditions
  • Homologous chromosomes
    Chromosomes of the same morphology with genes in the same location; diploid organisms have pairs of homologous chromosomes (homologs), with each homolog derived from a different parent
  • Homologous recombination
    Process by which homologous chromosomes undergo reciprocal physical exchanges at their arms, also known as crossing over
  • Homologous structures
    Parallel structures in diverse organisms that have a common ancestor
  • Homozygous
    Having two identical alleles for a given gene on the homologous chromosome
  • Honest signal
    Trait that gives a truthful impression of an individual’s fitness
  • Hormone
    chemical signaling molecule, usually protein or steroid, secreted by endocrine cells that act to control or regulate specific physiological processes
  • Host DNA
    DNA that is present in the genome of the organism of interest
  • Hybrid
    Offspring of two closely related individuals, not of the same species
  • Hybrid zone
    Area where two closely related species continue to interact and reproduce, forming hybrids
  • Hybridization
    Process of mating two individuals that differ with the goal of achieving a certain characteristic in their offspring
  • Hydrocarbon
    Molecule that consists only of carbon and hydrogen
  • Hydrogen bond
    Weak bond between slightly positively charged hydrogen atoms and slightly negatively charged atoms in other molecules
  • Hydrolysis
    Reaction that causes the breakdown of larger molecules into smaller molecules with the utilization of water
  • Hydrophilic
    Describes ions or polar molecules that interact well with other polar molecules such as water
  • Hydrophobic
    Molecule that does not have the ability to bond with water; “water-hating”
  • Hypertonic
    Situation in which extracellular fluid has a higher osmolarity than the fluid inside the cell, resulting in water moving out of the cell
  • Hypotonic
    Situation in which extracellular fluid has a lower osmolarity than the fluid inside the cell, resulting in water moving into the cell
  • Ileum
    Last part of the small intestine; connects the small intestine to the large intestine; important for absorption of B-12
  • Inbreeding
    Mating of closely related individuals
  • Inbreeding depression
    Increase in abnormalities and disease in inbreeding populations
  • Incomplete dominance
    In a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype
  • Induced fit
    Dynamic fit between the enzyme and its substrate, in which both components modify their structures to allow for ideal binding
  • Induced mutation
    Mutation that results from exposure to chemicals or environmental agents
  • Inert gas
    (also, noble gas) element with filled outer electron shell that is unreactive with other atoms
  • Ingestion
    Act of taking in food
  • Inhibitor
    Molecule that binds to a protein (usually an enzyme) and keeps it from functioning
  • Inositol phospholipid
    Lipid present at small concentrations in the plasma membrane that is converted into a second messenger; it has inositol (a carbohydrate) as its hydrophilic head group
  • Inositol triphosphate
    Cleavage product of PIP2 that is used for signaling within the cell
  • Integral protein
    Protein integrated into the membrane structure that interacts extensively with the hydrocarbon chains of membrane lipids and often spans the membrane; these proteins can be removed only by the disruption of the membrane by detergents
  • Intercellular signaling
    Communication between cells
  • Interkinesis
    Brief period of rest between meiosis I and meiosis II
  • Intermediate filament
    cytoskeletal component, composed of several intertwined strands of fibrous protein, that bears tension, supports cell-cell junctions, and anchors cells to extracellular structures
  • Internal receptor
    Receptor protein that is located in the cytosol of a cell and binds to ligands that pass through the plasma membrane
  • Interphase
    Period of the cell cycle leading up to mitosis; includes G1, S, and G2 phases (the interim period between two consecutive cell divisions
  • Interphase II
    Brief period of rest between meiosis I and meiosis II
  • Intestinal phase
    Third digestive phase; begins when chyme enters the small intestine triggering digestive secretions and controlling the rate of gastric emptying
  • Intracellular mediator
    Small molecule that transmits signals within a cell
  • Intracellular receptor
    Receptor protein that is located in the cytosol of a cell and binds to ligands that pass through the plasma membrane
  • Intracellular signaling
    Communication within cells
  • Ion
    Atom or chemical group that does not contain equal numbers of protons and electrons
  • Ion channel-linked receptor
    Cell-surface receptor that forms a plasma membrane channel, which opens when a ligand binds to the extracellular domain (ligand-gated channels)
  • Ionic bond
    Chemical bond that forms between ions with opposite charges (cations and anions)
  • IP3
    Cleavage product of PIP2 that is used for signaling within the cell
  • Isomerase
    Enzyme that converts a molecule into its isomer
  • Isotonic
    Iituation in which the extracellular fluid has the same osmolarity as the fluid inside the cell, resulting in no net movement of water into or out of the cell
  • Isotope
    One or more forms of an element that have different numbers of neutrons
  • Jejunum
    Second part of the small intestine
  • Karyogram
    Photographic image of a karyotype
  • Karyokinesis
    Period of the cell cycle during which the duplicated chromosomes are separated into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase
  • Karyotype
    Number and appearance of an individuals chromosomes; includes the size, banding patterns, and centromere position
  • Kinase
    Enzyme that catalyzes the transfer of a phosphate group from ATP to another molecule
  • Kinetic energy
    Type of energy associated with objects or particles in motion
  • Kinetochore
    Protein structure associated with the centromere of each sister chromatid that attracts and binds spindle microtubules during prometaphase
  • Krebs cycle
    Alternate name for the citric acid cycle, named after Hans Krebs who first identified the steps in the pathway in the 1930s in pigeon flight muscles; see citric acid cycle
  • Lactase
    Enzyme that breaks down lactose into glucose and galactose
  • Lagging strand
    During replication, the strand that is replicated in short fragments and away from the replication fork
  • Large intestine
    Digestive system organ that reabsorbs water from undigested material and processes waste matter
  • Law of dominance
    In a heterozygote, one trait will conceal the presence of another trait for the same characteristic
  • Law of independent assortment
    Genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur
  • Law of mass action
    Chemical law stating that the rate of a reaction is proportional to the concentration of the reacting substances
  • Law of segregation
    Paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors
  • Leading strand
    Strand that is synthesized continuously in the 5'-3' direction which is synthesized in the direction of the replication fork
  • Life cycle
    The sequence of events in the development of an organism and the production of cells that produce offspring
  • Ligand
    Molecule produced by a signaling cell that binds with a specific receptor, delivering a signal in the process
  • Ligase
    Enzyme that catalyzes the formation of a phosphodiester linkage between the 3' OH and 5' phosphate ends of the DNA
  • Light-dependent reaction
    First stage of photosynthesis where certain wavelengths of the visible light are absorbed to form two energy-carrying molecules (ATP and NADPH)
  • Light harvesting complex
    Complex that passes energy from sunlight to the reaction center in each photosystem; it consists of multiple antenna proteins that contain a mixture of 300–400 chlorophyll a and b molecules as well as other pigments like carotenoids
  • Light-independent reaction
    Second stage of photosynthesis, through which carbon dioxide is used to build carbohydrate molecules using energy from ATP and NADPH
  • Light microscope
    an instrument that magnifies an object using a beam visible light passed and bent through a lens system to visualize a specimen
  • Linkage
    Phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together
  • Linkage analysis
    Procedure that analyzes the recombination of genes to determine if they are linked
  • Lipase
    Enzyme that chemically breaks down lipids
  • Lipid
    Macromolecule that is nonpolar and insoluble in water
  • Litmus paper
    (also, pH paper) filter paper that has been treated with a natural water-soluble dye that changes its color as the pH of the environment changes so it can be used as a pH indicator
  • Liver
    Organ that produces bile for digestion and processes vitamins and lipids
  • Locus
    Position of a gene on a chromosome
  • Lysis buffer
    Solution used to break the cell membrane and release cell contents
  • Lysosome
    organelle in an animal cell that functions as the cell’s digestive component; it breaks down proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles
  • Macroevolution
    Broader scale evolutionary changes seen over paleontological time
  • Macromolecule
    Large molecule, typically formed by the joining of smaller molecules
  • Maltase
    Enzyme that breaks down maltose into glucose
  • Map unit
    Relative distance that corresponds to a recombination frequency of 0.01
  • Mass number
    Total number of protons and neutrons in an atom
  • Mating factor
    Signaling molecule secreted by yeast cells to communicate to nearby yeast cells that they are available to mate and communicating their mating orientation
  • MCS
    Site that can be recognized by multiple restriction endonucleases
  • Meiosis
    A nuclear division process that results in four haploid cells
  • Meiosis I
    First round of meiotic cell division; referred to as reduction division because the ploidy level is reduced from diploid to haploid
  • Meiosis II
    Second round of meiotic cell division following meiosis I; sister chromatids are separated into individual chromosomes, and the result is four unique haploid cells
  • Mesophyll
    Middle layer of chlorophyll-rich cells in a leaf
  • Metabolism
    All the chemical reactions that take place inside cells, including anabolism and catabolism
  • Metabolome
    Complete set of metabolites which are related to the genetic makeup of an organism
  • Metabolomics
    Study of small molecule metabolites found in an organism
  • Metagenomics
    Study of the collective genomes of multiple species that grow and interact in an environmental niche
  • Metaphase
    Stage of mitosis during which chromosomes are aligned at the metaphase plate
  • Metaphase plate
    Equatorial plane midway between the two poles of a cell where the chromosomes align during metaphase
  • Microevolution
    Changes in a population’s genetic structure
  • Microsatellite polymorphism
    Variation between individuals in the sequence and number of repeats of microsatellite DNA
  • Mineral
    Inorganic, elemental molecule that carries out important roles in the body
  • Mismatch repair
    Type of repair mechanism in which mismatched bases are removed after replication
  • Mitochondria
    (singular = mitochondrion) cellular organelles responsible for carrying out cellular respiration, resulting in the production of ATP, the cell’s main energy-carrying molecule
  • Mitosis
    Period of the cell cycle during which the duplicated chromosomes are separated into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase
  • Mitotic phase
    Period of the cell cycle during which duplicated chromosomes are distributed into two nuclei and cytoplasmic contents are divided; includes karyokinesis (mitosis) and cytokinesis
  • Mitotic spindle
    Apparatus composed of microtubules that orchestrates the movement of chromosomes during mitosis
  • Model organism
    Species that is studied and used as a model to understand the biological processes in other species represented by the model organism
  • Model system
    Species or biological system used to study a specific biological phenomenon to be applied to other different species
  • Modern synthesis
    Overarching evolutionary paradigm that took shape by the 1940s and is generally accepted today
  • Molecular cloning
    Cloning of DNA fragments
  • Molecule
    Chemical structure consisting of at least two atoms held together by one or more chemical bonds
  • Monogastric
    Digestive system that consists of a single-chambered stomach
  • Monohybrid
    Result of a cross between two true-breeding parents that express different traits for only one characteristic
  • Monomer
    The smallest unit of larger molecules called polymers
  • Monosaccharide
    Single unit or monomer of carbohydrates
  • Monosomy
    Otherwise diploid genotype in which one chromosome is missing
  • mRNA
    RNA that carries information from DNA to ribosomes during protein synthesis
  • Multiple cloning site
    Site that can be recognized by multiple restriction endonucleases
  • Mutation
    Variation in the nucleotide sequence of a genome
  • Natural selection
    Reproduction of individuals with favorable genetic traits that survive environmental change because of those traits, leading to evolutionary change
  • Neurotransmitter
    Chemical ligand that carries a signal from one nerve cell to the next
  • Neutron
    Uncharged particle that resides in the nucleus of an atom; has a mass of one amu noble gas see inert gas
  • Next-generation sequencing
    Group of automated techniques used for rapid DNA sequencing
  • Nondisjunction
    Failure of synapsed homologs to completely separate and migrate to separate poles during the first cell division of meiosis
  • Nonparental type
    Progeny resulting from homologous recombination that exhibits a different allele combination compared with its parents
  • Nonpolar covalent bond
    Type of covalent bond that forms between atoms when electrons are shared equally between them
  • Nonrandom mating
    Changes in a population’s gene pool due to mate choice or other forces that cause individuals to mate with certain phenotypes more than others
  • Northern blotting
    Transfer of RNA from a gel to a nylon membrane
  • Nuclear envelope
    Double-membrane structure that constitutes the outermost portion of the nucleus
  • Nucleoid
    Central part of a prokaryotic cell in which the chromosome is found
  • Nucleolus
    Darkly staining body within the nucleus that is responsible for assembling the subunits of the ribosomes
  • Nucleoplasm
    Semi-solid fluid inside the nucleus that contains the chromatin and nucleolus
  • Nucleosome
    Subunit of chromatin composed of a short length of DNA wrapped around a core of histone proteins
  • Nucleotide
    Monomer of nucleic acids; contains a pentose sugar, one or more phosphate groups, and a nitrogenous base
  • Nucleotide excision repair
    Type of DNA repair mechanism in which the wrong base, along with a few nucleotides upstream or downstream, are removed
  • Okazaki fragment
    DNA fragment that is synthesized in short stretches on the lagging strand
  • Omega fat
    Type of polyunsaturated fat that is required by the body; the numbering of the carbon omega starts from the methyl end or the end that is farthest from the carboxylic end
  • Omnivore
    Animal that consumes both plants and animals
  • Oncogene
    Mutated version of a normal gene involved in the positive regulation of the cell cycle
  • Organ
    Collection of related tissues grouped together performing a common function
  • Organ system
    Level of organization that consists of functionally related interacting organs
  • ORI
    Region of the prokaryotic chromosome where replication begins (origin of replication)
  • Origin
    Region of the prokaryotic chromosome where replication begins (origin of replication)
  • Osmolarity
    Total amount of substances dissolved in a specific amount of solution
  • Osmosis
    Transport of water through a semipermeable membrane according to the concentration gradient of water across the membrane that results from the presence of solute that cannot pass through the membrane
  • Oxidative phosphorylation
    Production of ATP using the process of chemiosmosis and oxygen
  • p21
    Cell cycle regulatory protein that inhibits the cell cycle; its levels are controlled by p53
  • p53
    Cell cycle regulatory protein that regulates cell growth and monitors DNA damage; it halts the progression of the cell cycle in cases of DNA damage and may induce apoptosis
  • P680
    Reaction center of photosystem II
  • P700
    Reaction center of photosystem I
  • Pancreas
    Gland that secretes digestive juices
  • Paracentric
    Inversion that occurs outside of the centromere
  • Paracrine signal
    Signal between nearby cells that is delivered by ligands traveling in the liquid medium in the space between the cells
  • Parental types
    Progeny that exhibits the same allelic combination as its parents
  • Passive transport
    Method of transporting material through a membrane that does not require energy
  • PCR
    Polymerase chain reaction; technique used to amplify DNA
  • Pepsin
    Enzyme found in the stomach whose main role is protein digestion
  • Pepsinogen
    Inactive form of pepsin
  • Peptide bond
    Bond formed between two amino acids by a dehydration reaction
  • Pericentric
    Inversion that involves the centromere
  • Peripheral protein
    Protein found at the surface of a plasma membrane either on its exterior or interior side
  • Peristalsis
    Wave-like movements of muscle tissue
  • pH scale
    Scale ranging from zero to 14 that is inversely proportional to the concentration of hydrogen ions in a solution
  • Pharmacogenomics
    Study of drug interactions with the genome or proteome; also called toxicogenomics
  • Phenotype
    Observable traits expressed by an organism
  • Phosphatase
    Enzyme that removes the phosphate group from a molecule that has been previously phosphorylated
  • Phosphoanhydride bond
    bond that connects phosphates in an ATP molecule
  • Phosphodiester bond
    The covalent chemical bond that holds together the polynucleotide chains, with a phosphate group linking two pentose sugars of neighboring nucleotides.
  • Phosphodiesterase
    Enzyme that degrades cAMP, producing AMP, to terminate signaling
  • Phospholipid
    Major constituent of the membranes; composed of two fatty acids and a phosphate-containing group attached to a glycerol backbone
  • Phosphorylation
    Addition of a high-energy phosphate to a compound, usually a metabolic intermediate, a protein, or ADP
  • Photoact
    Ejection of an electron from a reaction center using the energy of an absorbed photon
  • Photoautotroph
    Organism capable of producing its own organic compounds from sunlight
  • Photon
    Distinct quantity or “packet” of light energy
  • Photosystem
    Group of proteins, chlorophyll, and other pigments that are used in the light-dependent reactions of photosynthesis to absorb light energy and convert it into chemical energy
  • photosystem I
    Integral pigment and protein complex in thylakoid membranes that uses light energy to transport electrons from plastocyanin to NADP+ (which becomes reduced to NADPH in the process)
  • Photosystem II
    Integral protein and pigment complex in thylakoid membranes that transports electrons from water to the electron transport chain; oxygen is a product of PSII
  • Physical map
    Representation of the physical distance between genes or genetic markers
  • Pigment
    Molecule that is capable of absorbing certain wavelengths of light and reflecting others (which accounts for its color)
  • Pinocytosis
    A variation of endocytosis that imports macromolecules that the cell needs from the extracellular fluid
  • PKA
    Kinase that is activated by binding to cAMP
  • Plasma membrane
    Phospholipid bilayer with embedded (integral) or attached (peripheral) proteins, that separates the internal content of the cell from its surrounding environment
  • Plasmodesma
    (plural = plasmodesmata) Channel that passes between the cell walls of adjacent plant cells, connects their cytoplasm and allows materials to be transported from cell to cell
  • Plasmolysis
    Detaching of the cell membrane from the cell wall and constriction of the cell membrane when a plant cell is in a hypertonic solution
  • Point mutation
    Mutation that affects a single base
  • Polar covalent bond
    Type of covalent bond that forms as a result of unequal sharing of electrons, resulting in the creation of slightly positive and slightly negative charged regions of the molecule
  • Polygenic
    Phenotypic characteristic caused by two or more genes
  • Polymerase chain reaction
    Technique used to amplify DNA
  • Polymorphisms
    Variations in phenotype within individuals of a population
  • Polypeptide
    Long chain of amino acids linked by peptide bonds
  • Polyploid
    Individual with an incorrect number of chromosome sets
  • Polyploidy
    Gametes with extra chromosomes
  • Polysaccharide
    Long chain of monosaccharides; may be branched or unbranched
  • Population genetics
    Study of how selective forces change the allele frequencies in a population over time
  • Population variation
    Distribution of phenotypes in a population
  • Postzygotic barrier
    Reproductive isolation mechanism that occurs after zygote formation
  • Potential energy
    Type of energy that has the potential to do work; stored energy
  • Potocytosis
    Variation of pinocytosis that uses a different coating protein (caveolin) on the cytoplasmic side of the plasma membrane
  • Prezygotic barrier
    Reproductive isolation mechanism that occurs before zygote formation
  • Primary active transport
    Active transport that moves ions or small molecules across a membrane and may create a difference in charge across that membrane
  • Primary electron acceptor
    Pigment or other organic molecule in the reaction center that accepts an energized electron from the reaction center
  • Primase
    Enzyme that synthesizes the RNA primer; the primer is needed for DNA pol to start synthesis of a new DNA strand
  • Primer
    Short stretch of nucleotides that is required to initiate replication; in the case of replication, the primer has RNA nucleotides
  • Probe
    Small DNA fragment used to determine if the complementary sequence is present in a DNA sample
  • Product rule
    Probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone
  • Prokaryote
    Unicellular organism that lacks a nucleus or any other membrane-bound organelle
  • Prometaphase
    Stage of mitosis during which the nuclear membrane breaks down and mitotic spindle fibers attach to kinetochores
  • Proofreading
    Function of DNA pol in which it reads the newly added base before adding the next one
  • Prophase
    Stage of mitosis during which chromosomes condense and the mitotic spindle begins to form
  • Prosthetic cofactor
    Molecule bound to a protein that facilitates the function of the protein
  • Prosthetic group
    Molecule bound to a protein that facilitates the function of the protein
  • Protease
    Enzyme that breaks down proteins
  • Protein kinase A
    Kinase that is activated by binding to cAMP
  • Protein signature
    Set of uniquely expressed proteins in the diseased state
  • Proteome
    Entire set of proteins produced by a cell type
  • Proteomics
    Study of the function of proteomes
  • Proto-oncogene
    Normal gene that when mutated becomes an oncogene
  • Proton
    Positively charged particle that resides in the nucleus of an atom; has a mass of one amu and a charge of +1
  • Proventriculus
    Glandular part of a bird’s stomach
  • Pump
    Active transport mechanism that works against electrochemical gradients
  • Punctuated equilibrium
    Model for rapid speciation that can occur when an event causes a small portion of a population to be cut off from the rest of the population
  • Punnett square
    Visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid
  • Pure culture
    Growth of a single type of cell in the laboratory
  • Purine
    Type of nitrogenous base in DNA and RNA; adenine and guanine are purines
  • Pyrimidine
    Type of nitrogenous base in DNA and RNA; cytosine, thymine, and uracil are pyrimidines
  • Pyruvate
    Three-carbon sugar that can be decarboxylated and oxidized to make acetyl CoA, which enters the citric acid cycle under aerobic conditions; the end product of glycolysis
  • Quiescent
    Refers to a cell that is performing normal cell functions and has not initiated preparations for cell division
  • Quorum sensing
    Method of cellular communication used by bacteria that informs them of the abundance of similar (or different) bacteria in the environment
  • Radiation hybrid mapping
    Information obtained by fragmenting the chromosome with x-rays
  • Rb
    Regulatory molecule that exhibits negative effects on the cell cycle by interacting with a transcription factor (E2F)
  • Reaction center
    Complex of chlorophyll molecules and other organic molecules that is assembled around a special pair of chlorophyll molecules and a primary electron acceptor; capable of undergoing oxidation and reduction
  • Receptor
    Protein in or on a target cell that bind to ligands
  • Receptor-mediated endocytosis
    Variation of endocytosis that involves the use of specific binding proteins in the plasma membrane for specific molecules or particles, and clathrin-coated pits that become clathrin-coated vesicles
  • Receptor proteins
    Interaction of two receptor proteins to form a functional complex called a dimer
  • Recessive
    Trait that appears “latent” or non-expressed when the individual also carries a dominant trait for that same characteristic; when present as two identical copies, the recessive trait is expressed
  • Recessive lethal
    Inheritance pattern in which an allele is only lethal in the homozygous form; the heterozygote may be normal or have some altered, non-lethal phenotype
  • Reciprocal cross
    Paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross
  • Recombinant DNA
    Combination of DNA fragments generated by molecular cloning that does not exist in nature; also known as a chimeric molecule
  • Recombinant protein
    Protein product of a gene derived by molecular cloning
  • Recombinant type
    Progeny resulting from homologous recombination that exhibits a different allele combination compared with its parents
  • Recombination frequency
    Average number of crossovers between two alleles; observed as the number of nonparental types in a population of progeny
  • Recombination nodules
    Protein assemblies formed on the synaptonemal complex that mark the points of crossover events and mediate the multistep process of genetic recombination between non-sister chromatids
  • Rectum
    Area of the body where feces is stored until elimination
  • Redox reaction
    Chemical reaction that consists of the coupling of an oxidation reaction and a reduction reaction
  • Reduction
    Gain of electron(s) by an atom or molecule
  • Reduction division
    Nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division
  • Reinforcement
    Continued speciation divergence between two related species due to low fitness of hybrids between them
  • Relative fitness
    Individual’s ability to survive and reproduce relative to the rest of the population
  • Replication fork
    Y-shaped structure formed during initiation of replication
  • Reproductive cloning
    Cloning of entire organisms
  • Reproductive isolation
    Situation that occurs when a species is reproductively independent from other species; this may be brought about by behavior, location, or reproductive barriers
  • RER
    Region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification and phospholipid synthesis
  • Rermentation
    Process of regenerating NAD+ with either an inorganic or organic compound serving as the final electron acceptor; occurs in the absence of oxygen
  • Restriction endonuclease
    Enzyme that can recognize and cleave specific DNA sequences
  • Restriction fragment length polymorphism
    Variation between individuals in the length of DNA fragments generated by restriction endonucleases
  • Retinoblastoma protein
    Regulatory molecule that exhibits negative effects on the cell cycle by interacting with a transcription factor (E2F)
  • Reverse genetics
    Method of determining the function of a gene by starting with the gene itself instead of starting with the gene product
  • Reverse transcriptase PCR
    PCR technique that involves converting RNA to DNA by reverse transcriptase
  • RFLP
    Restriction fragment length polymorphism ; variation between individuals in the length of DNA fragments generated by restriction endonucleases
  • Ribonuclease
    Enzyme that breaks down RNA
  • Ribosome
    Cellular structure that carries out protein synthesis
  • Rough endoplasmic reticulum
    Region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification and phospholipid synthesis
  • Roughage
    Component of food that is low in energy and high in fiber
  • RT-PCR
    Reverse transcriptase PCR; PCR technique that involves converting RNA to DNA by reverse transcriptase
  • Ruminant
    Animal with a stomach divided into four compartments
  • S phase
    Second, or synthesis, stage of interphase during which DNA replication occurs
  • Salivary amylase
    Enzyme found in saliva, which converts carbohydrates to maltose
  • Second gap
    Third phase of interphase during which the cell undergoes final preparations for mitosis
  • Second messenger
    Small, non-protein molecule that propagates a signal within the cell after activation of a receptor causes its release
  • Secondary active transport
    Movement of material that is due to the electrochemical gradient established by primary active transport
  • Secretin
    Hormone which stimulates sodium bicarbonate secretion in the small intestine
  • Selective pressure
    Environmental factor that causes one phenotype to be better than another
  • Selectively permeable
    Characteristic of a membrane that allows some substances through but not others
  • Septum
    Cell biology: Structure formed in a bacterial cell as a precursor to the separation of the cell into two daughter cells | Anatomy: The septum of the heart is the dividing wall between the right and left sides of the heart.
  • Sequence mapping
    Mapping information obtained after DNA sequencing
  • SER
    Region of the endoplasmic reticulum that has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; detoxifies certain chemicals (like pesticides, preservatives, medications, and environmental pollutants), and stores calcium ions
  • Sex-linked
    Any gene on a sex chromosome
  • Sexual dimorphism
    Phenotypic difference between the males and females of a population
  • Shotgun sequencing
    Method used to sequence multiple DNA fragments to generate the sequence of a large piece of DNA
  • Signal integration
    Interaction of signals from two or more different cell-surface receptors that merge to activate the same response in the cell
  • Signal transduction
    Propagation of the signal through the cytoplasm (and sometimes also the nucleus) of the cell
  • Signaling cascade
    Chain of events that occurs in the cytoplasm of the cell to propagate the signal from the plasma membrane to produce a response
  • Signaling cell
    Cell that releases signal molecules that allow communication with another cell
  • Signaling pathway
    Chain of events that occurs in the cytoplasm of the cell to propagate the signal from the plasma membrane to produce a response
  • Silent mutation
    Mutation that is not expressed
  • Single nucleotide polymorphism
    Variation between individuals in a single nucleotide
  • Single-strand binding protein
    During replication, protein that binds to the single-stranded DNA; this helps in keeping the two strands of DNA apart so that they may serve as templates
  • Sliding clamp
    Ring-shaped protein that holds the DNA pol on the DNA strand
  • Small intestine
    Organ where digestion of protein, fats, and carbohydrates is completed
  • Smooth endoplasmic reticulum
    Region of the endoplasmic reticulum that has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; detoxifies certain chemicals (like pesticides, preservatives, medications, and environmental pollutants), and stores calcium ions
  • SNP
    Single nucleotide polymorphism; variation between individuals in a single nucleotide
  • Solute
    Substance dissolved in a liquid to form a solution
  • Somatic cell
    All the cells of a multicellular organism except the gametes or reproductive cells
  • Somatostatin
    Hormone released to stop acid secretion when the stomach is empty
  • Southern blotting
    Transfer of DNA from a gel to a nylon membrane
  • Speciation
    Formation of a new species
  • Species
    Group of populations that interbreed and produce fertile offspring
  • Specific heat capacity
    The amount of heat one gram of a substance must absorb or lose to change its temperature by one degree Celsius
  • Spectrophotometer
    Instrument that can measure transmitted light and compute the absorption
  • Sphere of hydration
    When polar water molecules surround charged or polar molecules thus keeping them dissolved and in solution
  • Sphincter
    Band of muscle that controls movement of materials throughout the digestive tract
  • Spontaneous mutation
    Mutation that takes place in the cells as a result of chemical reactions taking place naturally without exposure to any external agent
  • Spore
    Haploid cell that can produce a haploid multicellular organism or can fuse with another spore to form a diploid cell
  • Sporophyte
    A multicellular diploid life-cycle stage that produces haploid spores by meiosis
  • Stabilizing selection
    Selection that favors average phenotypes
  • Steroid
    Type of lipid composed of four fused hydrocarbon rings forming a planar structure
  • Stoma
    Opening that regulates gas exchange and water evaporation between leaves and the environment, typically situated on the underside of leaves
  • Stomach
    Saclike organ containing acidic digestive juices
  • Stroma
    Fluid-filled space surrounding the grana inside a chloroplast where the light-independent reactions of photosynthesis take place
  • Structural isomers
    Molecules that share a chemical formula but differ in the placement of their chemical bonds
  • Substrate
    Molecule on which the enzyme acts
  • Substrate-level phosphorylation
    Production of ATP from ADP using the excess energy from a chemical reaction and a phosphate group from a reactant
  • Sucrase
    Enzyme that breaks down sucrose into glucose and fructose
  • Sum rule
    Probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities
  • Surface tension
    Tension at the surface of a body of liquid that prevents the molecules from separating; created by the attractive cohesive forces between the molecules of the liquid
  • Sympatric speciation
    Speciation that occurs in the same geographic space
  • Symporter
    Transporter that carries two different ions or small molecules, both in the same direction
  • Synapsis
    Formation of a close association between homologous chromosomes during prophase I
  • Synaptic signal
    Chemical signal (neurotransmitter) that travels between nerve cells
  • Synaptonemal complex
    Protein lattice that forms between homologous chromosomes during prophase I, supporting crossover
  • Systems biology
    Study of whole biological systems (genomes and proteomes) based on interactions within the system
  • Target cell
    Cell that has a receptor for a signal or ligand from a signaling cell
  • TCA cycle
    Alternate name for the citric acid cycle, named after the group name for citric acid, tricarboxylic acid (TCA); see citric acid cycle
  • Telomerase
    Enzyme that contains a catalytic part and an inbuilt RNA template; it functions to maintain telomeres at chromosome ends
  • Telomere
    DNA at the end of linear chromosomes
  • Telophase
    Stage of mitosis during which chromosomes arrive at opposite poles, decondense, and are surrounded by a new nuclear envelope
  • Temporal isolation
    Differences in breeding schedules that can act as a form of prezygotic barrier leading to reproductive isolation
  • Test cross
    Cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait
  • Tetrad
    Two duplicated homologous chromosomes (four chromatids) bound together by chiasmata during prophase I
  • Theory of evolution
    Explains how populations change over time and how life diversifies the origin of species
  • Thermodynamics
    Study of energy and energy transfer involving physical matter
  • Thylakoid
    Disc-shaped, membrane-bound structure inside a chloroplast where the light-dependent reactions of photosynthesis take place; stacks of thylakoids are called grana
  • Thylakoid lumen
    Aqueous space bound by a thylakoid membrane where protons accumulate during light-driven electron transport
  • Ti plasmid
    Plasmid system derived from Agrobacterium tumifaciens that has been used by scientists to introduce foreign DNA into plant cells
  • Tight junction
    Firm seal between two adjacent animal cells created by protein adherence
  • Tissue
    Group of similar cells carrying out related functions.
  • Tonicity
    Amount of solute in a solution
  • Topoisomerase
    Enzyme that causes underwinding or overwinding of DNA when DNA replication is taking place
  • Trait
    Variation in the physical appearance of a heritable characteristic
  • Transcription
    Process through which messenger RNA forms on a template of DNA
  • Transformation
    Process in which external DNA is taken up by a cell
  • Transgenic
    Organism that receives DNA from a different species
  • Transition state
    High-energy, unstable state (an intermediate form between the substrate and the product) occurring during a chemical reaction
  • Transition substitution
    When a purine is replaced with a purine or a pyrimidine is replaced with another pyrimidine
  • Translation
    Process through which RNA directs the formation of protein
  • Translocation
    Process by which one segment of a chromosome dissociates and reattaches to a different, nonhomologous chromosome
  • Transport protein
    Membrane protein that facilitates passage of a substance across a membrane by binding it
  • Transporter
    Specific carrier proteins or pumps that facilitate movement
  • Transversion substitution
    When a purine is replaced by a pyrimidine or a pyrimidine is replaced by a purine
  • Trisomy
    Otherwise diploid genotype in which one entire chromosome is duplicated
  • Trypsin
    Pancreatic protease that breaks down protein
  • Tumor suppressor gene
    Segment of DNA that codes for regulator proteins that prevent the cell from undergoing uncontrolled division
  • Ubiquinone
    Soluble electron transporter in the electron transport chain that connects the first or second complex to the third
  • Unified cell theory
    A biological concept that states that all organisms are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells
  • Uniporter
    Transporter that carries one specific ion or molecule
  • Vacuole
    Membrane-bound sac, somewhat larger than a vesicle, which functions in cellular storage and transport
  • Valence shell
    Outermost shell of an atom
  • Van Der Waals
    Very weak interaction between molecules due to temporary charges attracting atoms that are very close together
  • Variable number of tandem repeats
    Variation in the number of tandem repeats between individuals in the population
  • Variation
    Genetic differences among individuals in a population
  • VDW
    (Van Der Waals) Very weak interaction between molecules due to temporary charges attracting atoms that are very close together
  • Vesicle
    Small, membrane-bound sac that functions in cellular storage and transport; its membrane is capable of fusing with the plasma membrane and the membranes of the endoplasmic reticulum and Golgi apparatus
  • Vestigial structure
    Physical structure present in an organism but that has no apparent function and appears to be from a functional structure in a distant ancestor
  • Vicariance
    Allopatric speciation that occurs when something in the environment separates organisms of the same species into separate groups
  • Villi
    Folds on the inner surface of the small intestine whose role is to increase absorption area
  • Vitamin
    Organic substance necessary in small amounts to sustain life
  • VNTRs
    Variable number of tandem repeats; variation in the number of tandem repeats between individuals in the population
  • Wavelength
    Distance between consecutive points of equal position (two crests or two troughs) of a wave in a graphic representation; inversely proportional to the energy of the radiation
  • Wax
    Lipid made of a long-chain fatty acid that is esterified to a long-chain alcohol; serves as a protective coating on some feathers, aquatic mammal fur, and leaves
  • Whole-genome sequencing
    Process that determines the DNA sequence of an entire genome
  • X inactivation
    Condensation of X chromosomes into Barr bodies during embryonic development in females to compensate for the double genetic dose
  • X-linked
    Gene present on the X, but not the Y chromosome