BIO - TERMS - FREQUENCY > 3

Question 1

acidosis

Answer 1

Condition in which the pH of arterial blood is below 7.35. // A condition in which an accumulation of H+ increases muscles acidity. // A metabolic condition in which the capacity of the body to buffer H is diminished; usually accompanied by decreased blood pH. // Abnormally low blood pH.

Question 2

active transport

Answer 2

Energy-requiring transport of a solute across a membrane in the direction of increasing concentration. // Movement of a molecule across a membrane or other barrier driven by energy other than that stored in the electrochemical or concentration gradient of the transported molecule. // Method of a protein pump transporting a substance across the membrane, against its concentration gradient. // Net movement of a substance across a membrane against a concentration gradient; requires the cell to expend energy.

Question 3

agonist

Answer 3

A compound, typically a hormone or neurotransmitter, that elicits a physiological response when it binds to its specific receptor. // Muscle that contracts to produce a particular movement; also called prime mover. // A stimulatory ligand for a receptor. // Organisms that produce substances (secondary metabolites) that activate defense mechanisms.

Question 4

aldose

Answer 4

A simple sugar in which the carbonyl carbon atom is an aldehyde; that is, the carbonyl carbon is at one end of the carbon chain. alkalosis A metabolic condition in which the capacity of the body to buffer OH is diminished; usually accompanied by an increase in blood pH. // A sugar that is an aldehyde. // Monosaccharide with an aldehyde group. // A type of carbohydrate with an aldehyde functional group.

Question 5

Allele (allelomorph; adj, allelic, allelomorphic)

Answer 5

Variation of a gene found on the same locus of homologous chromosomes. // A variant form of a gene; many genes occur in several (or more) different forms within the general population. See also heterozygous, homozygous, polymorphism. // One of several alternative forms of a gene. In a diploid cell, each gene will typically have two alleles, occupying the corresponding position (locus) on homologous chromosomes. // One of a pair, or series, of alternative forms of a gene that occur at a given locus in a chromosome. Alleles are symbolized with the same basic symbol (for example, D for tall peas and d for dwarf). (See also Multiple alleles.)

Question 6

aminoacyl-tRNA synthetase

Answer 6

Enzyme that attaches the correct amino acid to a tRNA molecule to form an aminoacyltRNA. // Enzymes that catalyze synthesis of an aminoacyl-tRNA at the expense of ATP energy. // Cytoplasmic enzymes that attach an amino acid to a tRNA. // Enzymes that catalyze the formation of high energy bonds between amino acids and tRNA molecules.

Question 7

anemia

Answer 7

Any condition in which the number of erythrocytes is below normal or the oxygen-carrying capacity of the blood is reduced (as may occur if the amount of hemoglobin within erythrocytes is decreased). // A decrease in the number of red blood cells, a decrease in the amount of hemoglobin, or any other condition leading to a decrease in the oxygen-carrying capacity of blood. // Abnormal condition characterized by pallor, weakness, and breathlessness, resulting from a deficiency of hemoglobin or a reduced number of red blood cells. // Abnormal decrease of the blood hemoglobin concentration.

Question 8

antigenic variation

Answer 8

Ability to change the antigens displayed on the cell surface; a property of some pathogenic microorganisms that enables them to evade attack by the adaptive immune system. // Alterations in surface antigens that occur in some pathogens (such as African trypanosomes) from one generation to another, which allows them to evade preexisting antibodies. // Changes in surface antigens that occur in a microbial population. // Th e display by virus particles or infected cells of new protein sequences that are not recognized by antibodies or T cells that responded to previous infections. (Chapter 5)

Question 9

aquaporin (AQP) // aquaporin (water channel)

Answer 9

A member of a family of integral membrane proteins that mediate the flow of water across membranes. // Channel protein embedded in the plasma membrane that greatly increases the cell’s permeability to water, allowing transport of water, but not ions, at a high rate across the membrane. // (ak′wă-pōr-in) Protein channels in the plasma membrane allowing the passage of water. // Membrane-based proteins regulating water flow across the membrane.

Question 10

Atomic number, Z

Answer 10

Indicates the number of protons in one atom of a specific element. Value appears above each atomic symbol in the periodic table. // The number of protons in the nucleus of an atom. // The number of protons in an atom; the atomic number defines the element. // The number of protons in the nucleus of an atom.

Question 11

ATP (adenosine 5′-triphosphate)

Answer 11

Adenosine triphosphate: an energy-rich compound that promotes certain activities in the cell. // Nucleoside triphosphate composed of adenine, ribose, and three phosphate groups. The principal carrier of chemical energy in cells. The terminal phosphate groups are highly reactive in the sense that their hydrolysis, or transfer to another molecule, takes place with the release of a large amount of free energy. // A ribonucleoside 5’-triphosphate functioning as a phosphate group donor in the cellular energy cycle; carries chemical energy between metabolic pathways by serving as a shared intermediate coupling endergonic and exergonic reactions. // Chemical that transfers energy within a cell.

Question 12

autoimmune disease

Answer 12

Damage to one’s own organs due to action of the immune system. // Pathological state in which the body mounts a disabling adaptive immune response against one or more of its own molecules. // Disease in which the immune system attacks selfantigens as if they were foreign. // Disorders in which the immune systems of affected individuals produce antibodies against self antigens— antigens synthesized in their own cells.

Question 13

base

Answer 13

(1) A substance that can reduce the number of protons in solution, either by accepting H+ ions directly, or by releasing OH– ions, which then combine with H+ to form H2O. (2) The purines and pyrimidines in DNA and RNA are organic nitrogenous bases and are often referred to simply as bases. // A proton acceptor. // A substance that dissociates into one or more hydroxide ions (OH2) and one or more positive ions. // Substance that accepts a hydrogen ion.

Question 14

calorie (cal)

Answer 14

The amount of heat required to raise the temperature of 1.0 g of water from 14.5 to 15.5 C. One calorie (cal) equals 4.18 joules (J). // The amount of energy required to raise the temperature of 1 g of water by 1°C. // A unit of energy defined as the amount of energy required to raise 1 g of water 1°C; equal to 4.184 J. // Shorthand notation for the kilocalorie (kcal), or 1000 calories; also called the nutritional calorie, the unit of energy used on nutritional labels.

Question 15

capsid

Answer 15

The protein coat of a virion or virus particle. // The outer shell of viral proteins that surrounds the genome in a virus particle. (Chapters 1 and 4) // The protein coat of a virus that surrounds the nucleic acid. // The protein coat of the virus particle.

Question 16

caspase

Answer 16

Intracellular protease that is involved in mediating the intracellular events of apoptosis. // A family of cysteine proteases that cleave proteins at aspartic acid residues. They have important roles in apoptosis and in the processing of cytokine pro-polypeptides. // Crirical proteases in apoptosis; members of a family of cysteine proteases that specifically cleave after aspartate residues. (Chapter 3) // Proteases whose activation triggers apoptosis.

Question 17

catecholamines

Answer 17

(kat-ĕ-kōl′ă- mēnz) Class of neurotransmitters (includes epinephrine, norepinephrine, and dopamine). // Tyrosine-derived biogenic amines: dopamine, norepinephrine, and epinephrine. // Hormones, such as epinephrine, that are amino derivatives of catechol. // The neurotransmitters dopamine, norepinephrine, and epinephrine.

Question 18

centriole

Answer 18

(sen′trē-ōl) Organelle that participates in the separation of chromosome pairs or sister // Short cylindrical array of microtubules, closely similar in structure to a basal body. A pair of centrioles is usually found at the center of a centrosome in animal cells. // A structure consisting of nine microtubule triplets, found in eukaryotic cells. // An organelle in many animal cells that appears to be involved in the formation of the spindle during mitosis.

Question 19

centrosome

Answer 19

A barrel-shaped organelle associated with the mitotic spindle in animal cells. // Centrally located organelle of animal cells that is the primary microtubule-organizing center (MTOC) and acts as the spindle pole during mitosis. In most animal cells it contains a pair of centrioles. // Region in a eukaryotic cell consisting of a pericentriolar area (protein fibers) and a pair of centrioles; involved in formation of the mitotic spindle. // An organelle that is the main microtubule-organizing center. (Chapter 5)

Question 20

chemokine

Answer 20

A cytokine that induces, by chemotaxis, the migration of leukocytes into infected areas. // Small chemoattractant protein that stimulates the migration and activation of cells, especially phagocytic cells and lymphocytes. Chemokines have a central role in inflammatory responses. Properties of individual chemokines are listed in Appendix IV. // Small proteins that attract and stimulate cells of the immune defense system; produced by many cells in response to infection. (Chapter 3) // Small proteins that attract and stimulate cells of the immune defense; produced by many cells in response to infection. Also called chemotactic cytokines. (Chapter 5)

Question 21

cholesterol

Answer 21

An abundant lipid molecule with a characteristic four-ring steroid structure. An important component of the plasma membranes of animal cells. // The most common steroid (fat-like material) found in the human body; important for membrane fluidity and as a precursor to steroid hormones; high cholesterol levels are associated with an increased risk of coronary diseases. // The only important membrane steroid in humans. // Type of steroid found in the plasma membrane.

Question 22

Cilium (pl, cilia; adj, ciliate)

Answer 22

(sil′ē-ă) Extensions of plasma membrane supported by microtubules that move materials past the cell. // Hairlike locomotor structure on certain cells; a locomotor structure on a ciliate protozoan. cis-acting sequence. A nucleotide sequence that only affects the expression of genes located on the same chromosome, that is, cis to itself. // Hairlike extension of a eukaryotic cell containing a core bundle of microtubules. Many cells contain a single nonmotile cilium, while others contain large numbers that perform repeated beating movements. Compare flagellum. // A relatively short cellular projection from some eukaryotic cells, composed of nine pairs plus two microtubules. See flagellum.

Question 23

cofactor

Answer 23

(1) The nonprotein component of an enzyme. (2) A microorganism or molecule that acts with others to synergistically enhance or cause disease. // An inorganic ion or a coenzyme required for enzyme activity. // A small nonprotein part of an enzyme that is necessary for biological activity. // Inorganic chemical structure attached to an enzyme that aids in enzyme function; e.g., Zn2+.

Question 24

complementary DNA (cDNA)

Answer 24

A DNA complementary to a specific mRNA, used in DNA cloning; usually made by reverse transcriptase. // DNA made in vitro from an mRNA template. // The double-stranded DNA copy of a single-stranded RNA. // Transcribed from mRNA by employing the enzyme reverse transcriptase.

Question 25

conformation

Answer 25

A spatial arrangement of substituent groups that are free to assume different positions in space, without breaking any bonds, because of the freedom of bond rotation. // The folded, three-dimensional structure of a polypeptide chain. // The noncovalent higher-order structure of a protein. // The three-dimensional shape of a molecule at any given instant, assuming that rotation around single bonds is frozen.

Question 26

conjugation

Answer 26

A series of overlapping p orbitals, usually in alternating single and multiple bonds. For example, 1,3-butadiene is a conjugated diene, 3-buten-2-one is a conjugated enone, and benzene is a cyclic conjugated triene. // The transfer of genetic material from one cell to another involving cell-to-cell contact. // Transfer of a self-transmissible plasmid from one cell to another. // Union of sex cells (gametes) or unicellular organisms during fertilization; in Escherichia coli, a one-way transfer of genetic material from a donor (“male” cell) to a recipient (“female” cell).

Question 27

consensus sequence

Answer 27

Average or most typical form of a sequence that is reproduced with minor variations in a group of related DNA, RNA, or protein sequences. Indicates the nucleotide or amino acid most often found at each position. Preservation of a sequence implies that it is functionally important. // The sequence of the most commonly encountered bases in a functionally defined nucleic acid sequence. // A DNA or amino acid sequence consisting of the residues that most commonly occur at each position in a set of similar sequences.

Question 28

cytochrome

Answer 28

A protein that functions as an electron carrier in cellular respiration and photosynthesis. // Colored heme-containing protein that transfers electrons during respiration and photosynthesis. // Heme proteins serving as electron carriers in respiration, photosynthesis, and other oxidation-reduction reactions. // Heme proteins that function as electron carriers.

Question 29

cytokinesis

Answer 29

The final separation of daughter cells following mitosis. // (sı̄′tō-ki-nē′sis) Division of the cytoplasm during cell division. // Cytoplasmic division and other changes exclusive of nuclear division that are a part of mitosis or meiosis. // Division of the cytoplasm of a plant or animal cell into two, as distinct from the associated division of its nucleus (which is mitosis). Part of M phase.

Question 30

diapedesis

Answer 30

(dı̄′ă-pĕ-dē′sis) Passage of leukocytes (white blood cells) through the intact blood vessel wall. // Th e process by which viruses cross the vascular endothelium, while being carried within monocytes or lymphocytes. (Chapter 2) // The movement of blood cells, particularly leukocytes, from the blood across blood vessel walls into tissues. // The process by which phagocytes move out of blood vessels.

Question 31

diploid // diploid cell

Answer 31

(dip′loyd) State of a cell containing pairs of homologous chromosomes. In humans, the diploid number of chromosomes is 46 (23 pairs). // Having two sets of genetic information; describes a cell with two chromosomes of each type. Compare haploid. // An organism or cell with two sets of chromosomes (2n) or two genomes. Somatic tissues of higher plants and animals are ordinarily diploid in chromosome constitution in contrast with the haploid (monoploid) gametes. // A cell having two sets of chromosomes; diploid is the normal state of a eukaryotic cell.

Question 32

DNA ligase

Answer 32

Enzyme that joins the ends of two strands of DNA together with a covalent bond to make a continuous DNA strand. // An enzyme that catalyzes covalent closure of nicks in DNA double helices. // An enzyme that links two DNA strands. // Enzymes that creates a phosphodiester bond between the 3’ end of one DNA segment and the 5’ end of another.

Question 33

double helix

Answer 33

A DNA molecule composed of two complementary strands. // The natural coiled conformation of two complementary, antiparallel DNA chains. // The structure of DNA in which two polynucleotide strands coil around each other. // The three-dimensional structure of DNA, in which two antiparallel DNA chains, held together by hydrogenbonding between the bases, are wound into a helix.

Question 34

Enhancer

Answer 34

A DNA sequence containing multiple elements that can stimulate RNA polymerase II transcription over long distances, independently of orientation or location relative to the site of transcriptional initiation. (Chapter 8) // A substance or an object that increases a chemical activity or a physiological process; a major or modifier gene that increases a physiological process; a DNA sequence that influences transcription of a nearby gene. // DNA sequences that facilitate the expression of a given gene; may be located a few hundred, or even thousand, base pairs away from the gene. // DNA sequences that increase the rate of transcription by binding regulatory proteins.

Question 35

enthalpy (heat) of reaction (ΔHᵣₓₙ) // enthalpy change (DH) // Heat of reaction

Answer 35

The enthalpy change for a chemical reaction. // For a reaction, approximately equal to the difference between the energy used to break bonds and the energy gained by the formation of new ones. // The heat of reaction. The enthalpy change that occurs during a reaction is a measure of the difference in total bond energy between reactants and products. // An alternative name for the enthalpy change in a reaction, DH.

Question 36

entropy (S)

Answer 36

A thermodynamic function that is proportional to the number of energetically equivalent ways to arrange the components of a system to achieve a particular state; a measure of the energy randomization or energy dispersal in a system. // The randomness of a thermodynamic system. // The extent of randomness or disorder in a system. // Thermodynamic quantity that measures the degree of disorder or randomness in a system; the higher the entropy, the greater the disorder.

Question 37

epithelial // epithelial cell // epithelial tissues

Answer 37

A type of tissue or cell that may line surfaces or cavities of various structures and organs in the body. // Any cell that forms part of the outer covering of an organism or organ. // A type of cell that composes tissues that line the surfaces of structures or cavities in organisms. // Tissues, such as the lining of the gut or the epidermal covering of the skin, in which cells are closely bound together into sheets called epithelia.

Question 38

epitope

Answer 38

A short contiguous sequence or unique conformation of a macromolecule that can be recognized by the immune system; also called an antigenic determinant; a T cell epitope is a short peptide recognized by a particular T cell receptor, while a B cell epitope is recognized by the antigen-binding domain of antibody and is part of an intact protein. (Chapter 2) // A site on an antigen recognized by an antibody or an antigen receptor. T-cell epitopes are short peptide bound to MHC molecules. B-cell epitopes are typically structural motifs on the surface of the antigen. Also called an antigenic determinant. // An antigenic determinant; the particular chemical group or groups in a macromolecule (antigen) to which a given antibody binds. // Th e parts of an antigen that are bound by an antibody or that are recognized by a T cell receptor in the context of major histocompatibility proteins. (Chapter 4)

Question 39

equilibrium constant (K // Keq)

Answer 39

A thermodynamic constant that is defined as product concentration(s) divided by substrate concentration(s) at equilibrium. // The ratio, at equilibrium, of the concentrations of the products of a reaction raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients. // The ratio of forward and reverse rate constants for a reaction. Equal to the association or affinity constant (Ka) for a simple binding reaction (A + B AB). See also affinity constant, dissociation constant. // A constant, characteristic for each chemical reaction, that relates the specific concentrations of all reactants and products at equilibrium at a given temperature and pressure.

Question 40

erythrocyte // red blood cell

Answer 40

(ĕ-rith′rō-sı̄t) Mature red blood cell. // A cell containing large amounts of hemoglobin and specialized for oxygen transport; a red blood cell. // Another name for a red blood cell, or the oxygen-carrying cell of the blood. erythropoiesis The cellular events involved in the production of red blood cells. // Small hemoglobin-containing blood cell of vertebrates that transports oxygen to, and carbon dioxide from, tissues. Also called an erythrocyte.

Question 41

essential oil (EO) // volatile oil

Answer 41

The volatile oil obtained by steam distillation of a plant extract. // Mixture of volatile terpenoids and phenylpropanoids responsible for the taste and smell of many plants, especially spices. // Volatile oils extracted from plants; smell like the plant. // Blend of various terpenoids and phenylpropanoids that evaporate easily (they add taste and smell to many plants).

Question 42

Estrogen

Answer 42

Female hormone or estrus-producing compound. // 18-Carbon steroids, synthesized from androgens by the aromatization of ring A. // Female steroid sex hormones. // Female steroidal hormones, the most important of which are estradiol and progesterone.

Question 43

euchromatin

Answer 43

A dispersed, transcriptionally active form of chromatin. // Genetic material that is not stained so intensely by certain dyes during interphase and that comprises many different kinds of genes (cf. Heterochromatin). // Region of an interphase chromosome that stains diffusely; “normal” chromatin, as opposed to the more condensed heterochromatin. // The regions of interphase chromosomes that stain diffusely, as opposed to the more condensed, heavily staining, heterochromatin. These are often regions in which genes are being actively expressed.

Question 44

extrinsic pathway // extrinsic pathway of apoptosis

Answer 44

Pathway of apoptosis triggered by extracellular signal proteins binding to cell-surface death receptors. // In blood clotting, the process by which prothrombin is activated through a series of reactions. Factor VII (a vitamin K–dependent protein) is activated by a tissue factor called thromboplastin. Activated factor VII then activates factor X, which activates prothrombin. // Pathway by which apoptosis is induced when a proapoptotic ligand binds to its cell surface receptor. (Chapter 3) // A pathway triggered by extracellular ligands binding to specific cell-surface receptors (death receptors) that signal the cell to undergo programmed cell death (apoptosis).

Question 45

facilitated diffusion

Answer 45

The movement of a substance across a plasma membrane from an area of higher concentration to an area of lower concentration, mediated by transporter proteins. // A passive type of carrier-mediated transport. // Movement of a substance across a membrane, via a transport protein, down a gradient (e.g., concentration, electric). // Passive transport process using carrier proteins or channel proteins to move a chemical across the plasma membrane.

Question 46

fatty acid

Answer 46

A carboxylic acid with a long hydrocarbon tail. // A long-chain aliphatic carboxylic acid found in natural fats and oils; also a component of membrane phospholipids and glycolipids. // A hydrocarbon chain with a carboxyl group as the terminal carbon. The chain may have double bonds or be completely saturated. // A long, straight-chain carboxylic acid found in fats and oils.

Question 47

Fluorescence in situ hybridization // Fluorescent in situ hybridization (FISH)

Answer 47

Fluorescent in situ hybridization; use of rRNA probes to identify microbes without culturing. // In situ hybridization performed using a DNA or RNA probe coupled to a fluorescent dye. // A cytogenetic technique developed by biomedical researchers in the early 1980s that is used to detect and localize the presence or absence of specific DNA sequences on chromosomes. // Method for the detection of DNA sequences in a chromosome spread.

Question 48

frameshift mutation

Answer 48

Mutation deleting or inserting of one or two nucleotides in a gene. This shifts the normal reading frame and causes the formation of functionless proteins. // Insertion or deletion that changes the reading frame of the messenger RNA. // A mutation caused by the addition or deletion of one or more bases in DNA. // A mutation that changes the reading frame of an mRNA, either by inserting or deleting nucleotides.

Question 49

free energy (G) (Gibbs free energy)

Answer 49

The “useful” energy in chemical reactions. // The component of the total energy of a system that can do work at constant temperature and pressure. // The energy that can be extracted from a system to drive reactions. Takes into account changes in both energy and entropy // A thermodynamic state function related to enthalpy and entropy by the equation G = H - TS; chemical systems tend toward lower Gibbs free energy, also called the chemical potential.

Question 50

functional group

Answer 50

A characteristic atom or group of atoms that impart certain chemical properties to an organic compound. // The specific atom or group of atoms that confers a particular chemical property on a biomolecule. // An arrangement of atoms in an organic molecule that is responsible for most of the chemical properties of that molecule. // 1. Classification of invertebrates into groups based on how they gather and eat food. Includes grazers, scrapers, shredders, collectors 2. specific groups within molecules that are responsible for specific chemical reactions of those.

Question 51

G protein–coupled receptors (GPCRs)

Answer 51

A large family of membrane receptor proteins with seven transmembrane helical segments, often associating with G proteins to transduce an extracellular signal into a change in cellular metabolism; also called heptahelical receptors. // A membrane protein that activates G-proteins when it binds neurotransmitter. // A seven-pass cellsurface receptor that, when activated by its extracellular ligand, activates a G protein, which in turn activates either an enzyme or ion channel in the plasma membrane. // A large class of seven-span transmembrane cell-surface receptors that associate with intracellular heterotrimeric G proteins after ligand binding, and signal by activation of the G protein. Important examples are the chemokine receptors.

Question 52

G0 // G0 state // G0 phase // Resting state

Answer 52

State of withdrawal from the eukaroytic cell-division cycle by entry into a quiescent digression from the G1 phase. A common, sometimes permanent, state for differentiated cells. // A state in which the cell has ceased to grow and divide and has withdrawn from the cell cycle. Also called resting state. (Chapter 9) // A state in which the cell has ceased to grow and divide and has withdrawn from the cell cycle. Also called G 0. (Chapter 6) // The nondividing state of a cell.

Question 53

gamete

Answer 53

(gam′ēt) A sex cell with the haploid number of chromosomes. // A male or female reproductive cell. // A mature male or female reproductive cell (sperm or egg). // Reproductive cells with a haploid gene content; sperm or egg cells.

Question 54

genetic code

Answer 54

The mRNA codons and the amino acids they encode. // The set of triplet code words in DNA (or mRNA) coding for the amino acids of proteins. // The set of 64 nucleotide triplets that specify the 20 amino acids and polypeptide chain initiation and termination. // The set of rules specifying the correspondence between nucleotide triplets (codons) in DNA or RNA and amino acids in proteins.

Question 55

genomics

Answer 55

A science devoted broadly to the understanding of cellular and organism genomes. // The study of genes and their function. // The study of the structure and function of entire genomes. // Determination of the whole DNA sequence of an organism and genome mapping on a fine scale by assigning DNA fragments to chromosomes.

Question 56

gluconeogenesis

Answer 56

The biosynthesis of a carbohydrate from simpler, noncarbohydrate precursors such as oxaloacetate or pyruvate. // (glū′kō-nē′ō- jen′ĕsis) Formation of glucose from a noncarbohydrate source. // Synthesis of glucose from noncarbohydrates. // The anabolic pathway by which organisms make glucose from simple three-carbon precursors.

Question 57

glycosaminoglycan (GAG)

Answer 57

A heteropolysaccharide of two alternating units one is either N-acetylglucosamine or N-acetylgalactosamine; the other is a uronic acid (usually glucuronic acid). Formerly called a mucopolysaccharide. // Long, linear, highly charged polysaccharide composed of a repeating pair of sugars, one of which is always an amino sugar. Mainly found covalently linked to a protein core in extracellular matrix proteoglycans. Examples include chondroitin sulfate, hyaluronan, and heparin. // A structurally unique polysaccharide that includes amino sugar (glucosamine or galactosamine); found in joints and connective tissue. // Polysaccharides containing an amino sugar in every other position.

Question 58

green fluorescent protein (GFP)

Answer 58

A naturally occurring fluorescent protein synthesized by the jellyfish Aequorea victoria. // A small protein from a marine organism that produces a bright fluorescence in the green region of the visible spectrum. Fusion proteins with GFP are commonly used to determine the subcellular location of the fused protein by fluorescence microscopy. // A jellyfish protein that can be expressed in mammalian neurons by genetic engineering, causing these neurons to fluoresce bright green when illuminated by the appropriate wavelength of light. // Fluorescent protein isolated from a jellyfish. Widely used as a marker in cell biology.

Question 59

hapten

Answer 59

(hap′ten) Small substance that attaches to another molecule to initiate an immune reaction. // A substance of low molecular mass that does not cause the formation of antibodies by itself but does so when combined with a carrier molecule. // A small molecule that, when linked to a larger molecule, elicits an immune response. // Any small molecule that can be recognized by a specific antibody but cannot by itself elicit an immune response. A hapten must be chemically linked to a protein molecule to elicit antibody and T-cell responses.

Question 60

helper CD4 T cells, helper T cells // CD4 cells // helper T (TH) lymphocyte // Helper T cells

Answer 60

Effector CD4 T cells that stimulate or ‘help’ B cells to make antibody in response to antigenic challenge. TH2, TH1, and the TFH subsets of effector CD4 T cells can perform this function. // (lim′fō-sı̄t) A T-lymphocyte that releases cytokines to regulate antibody-mediated immunity and cellular immunity as well as cells of innate immunity; also called CD4 cells. // Type of T cell that helps activate B cells to make antibodies, cytotoxic T cells to become effector cells, and macrophages to kill ingested pathogens. They can also help activate dendritic cells. // T cells that respond to an antigen displayed by a macrophage by stimulating B and T lymphocytes to develop into antibody-producing plasma cells and killer T cells, respectively.

Question 61

herd immunity

Answer 61

Immunity to a disease in a large portion of the population due to a history of active infections or vaccinations; provides other individuals in the population with indirect protection against that disease. // Protection conferred to unvaccinated individuals in a population produced by vaccination of others and reduction in the natural reservoir for infection. // Th e immune status of a population, rather than an individual. (Chapter 8) // The presence of immunity in most of a population.

Question 62

high-performance liquid chromatography (HPLC)

Answer 62

Chromatographic procedure, often conducted at relatively high pressures using automated equipment, which permits refined and highly reproducible profiles. // A technique used to analyze chemical compounds and extracts see Liquid Chromatography (LC). // Type of chromatography that uses columns packed with tiny beads of matrix; the solution to be separated is pushed through under high pressure. // High-pressure liquid chromatog raphy; a variant of column chromatography using high pressure to force solvent through very small absorbent particles.

Question 63

hybridization

Answer 63

In molecular biology, the process whereby two complementary nucleic acid strands form a base-paired duplex DNA-DNA, DNA-RNA, or RNA-RNA molecule. Forms the basis of a powerful technique for detecting specific nucleotide sequences. // A mathematical procedure in which standard atomic orbitals are combined to form new, hybrid orbitals. // Annealing of nucleic acids from different sources. // Interbreeding of species, races, varieties, and so on, among plants or animals; a process of forming a hybrid by cross pollination of plants or by mating animals of different types.

Question 64

hydrophobic interaction

Answer 64

Chemical interaction occurring between nearby hydrophobic moieties typically excluding water molecules. // The association of nonpolar groups or compounds with each other in aqueous systems, driven by the tendency of the surrounding water molecules to seek their most stable (disordered) state. // Association of nonpolar groups with each other when present in aqueous solutions because of their insolubility in water. // Interactions between hydrophobic groups, resulting from reduction of the aqueous-nonpolar interface.

Question 65

in vivo

Answer 65

“In life”; that is, in the living cell or organism. // In a living cell or organism. // A Latin word meaning “within a living organism.” // From the Latin meaning “within the living organism.”

Question 66

inositol-1,4,5-triphosphate (IP₃)

Answer 66

A second messenger formed by phospholipase C; releases calcium from the endoplasmic reticulum. // A soluble second messenger produced by the cleavage of membrane inositol phospholipids by phospholipase C-γ. It acts on receptors in the endoplasmic reticulum membrane, resulting in the release of stored Ca2+ into the cytosol. // Small intracellular signaling molecule produced during activation of the inositol phospholipid signaling pathway. Acts to release Ca2+ from the endoplasmic reticulum. // A second messenger molecule formed by the action of phospholipase C on the membrane phospholipid phosphatidylinositol-4,5-bisphosphate. IP₃ causes the release of Ca²⁺ from intracellular stores.

Question 67

integrin

Answer 67

One of a large family of heterodimeric transmembrane proteins that mediate adhesion of cells to other cells or to the extracellular matrix. // Heterodimeric cell-surface proteins involved in cell–cell and cell–matrix interactions. They are important in adhesive interactions between lymphocytes and antigen-presenting cells and in lymphocyte and leukocyte adherence to blood vessel walls and migration into tissues. // Transmembrane adhesion protein that is involved in the attachment of cells to the extracellular matrix and to each other. // Integral membrane proteins that function as receptors for components of the extracellular matrix.

Question 68

ionizing radiation

Answer 68

A type of radiation, such as x rays, that causes loss of electrons from some organic molecules, thus making them more reactive. // Energy-rich radiation that forms free radicals in the body. // High-energy radiation with a wavelength less than 1 nm; causes ionization. X rays and gamma rays are examples. // The portion of the electromagnetic spectrum that results in the production of positive and negative charges (ion pairs) in molecules. X rays and gamma rays are examples of ionizing radiation (cf. Nonionizing radiation).

Question 69

isotope

Answer 69

(ı̄′sō-tōp) Atoms of an element that have a different number of neutrons. // A form of a chemical element in which the number of neutrons in the nucleus is different from the other forms of that element. // Atoms of the same element with the same number of protons but different numbers of neutrons and consequently different masses. // Atoms of the same element that have different mass numbers.

Question 70

keratin

Answer 70

(ker′ă-tin) Protein that strengthens the epidermis, hair, and nails; produced by keratinocytes. // A protein found in epidermis, hair, and nails. // A type of intermediate filament protein in epithelial cells. // Type of intermediate filament, commonly produced by epithelial cells.

Question 71

ketone body

Answer 71

Acetoacetate, D–hydroxybutyrate, and acetone; water-soluble fuels normally exported by the liver but overproduced during fasting or in untreated diabetes mellitus. // Acetoacetate, β-hydroxybutyrate, and acetone. // Waste product of fatty acid breakdown; also called ketoacids. // A by-product of fatty acid breakdown that is water soluble and can be used for energy by the brain and heart.

Question 72

ketose

Answer 72

A simple monosaccharide in which the carbonyl group is a ketone. // Monosaccharide with a keto group. // A sugar that is a ketone. // Carbohydrates with a ketone functional group.

Question 73

kinase

Answer 73

(1) An enzyme that removes a P smallest size, for in text. from ATP and attaches it to another molecule. (2) A bacterial enzyme that breaks down fibrin (blood clots). // (kı̄′nās) Type of enzyme that transfers a phosphate group from one molecule to another. // An enzyme that transfers a phosphate group from a nucleotide. // Enzymes that catalyze the phosphorylation of certain molecules by ATP.

Question 74

kinetics

Answer 74

The description of reaction rates. // A dynamic process involving motion. // Referring to reaction rates. Kinetic measurements are useful for helping to determine reaction mechanisms. // The study of reaction rates.

Question 75

leading strand

Answer 75

The DNA strand that, during replication, is synthesized in the same direction as the replication fork moves. // The strand that is synthesized continuously during DNA replication. // The complement of the original 5’ → 3’ DNA strand that is synthesized continuously in a single piece. // The strand of DNA that is synthesized continuously during replication.

Question 76

leukotriene

Answer 76

Any of a class of signaling lipids derived from arachidonate in the noncyclic pathway; modulate smooth muscle activity. // A substance produced by mast cells and basophils that causes increased permeability of blood vessels and helps phagocytes attach to pathogens. // Biologically active products formed in asthma and other allergic diseases. // Lipid mediators of inflammation that are derived from arachidonic acid. They are produced by macrophages and other cells.

Question 77

lipase

Answer 77

An enzyme that breaks down triglycerides into their component glycerol and fatty acids. // Triglyceride-degrading enzyme. // (lip′ās) Enzyme that digests triglycerides. // Enzymes that catalyze the hydrolysis of triacylglycerols.

Question 78

lipoprotein

Answer 78

A complex in which proteins, triglycerides, phospholipids, and cholesterol are packaged to allow them to be water soluble so they can be transported in the blood. // A complex molecule with both lipid and protein parts that transports lipids through the body. // A lipid-protein aggregate that serves to carry water-insoluble lipids in the blood. The protein component alone is an apolipoprotein. // Noncovalent aggregates of protein and lipid.

Question 79

macrophage

Answer 79

Phagocytic cell derived from monocytes that serves as an antigenpresenting cell for T-lymphocytes. // A phagocytic cell; a mature monocyte. See fixed macrophage, free wandering macrophage. // Phagocytic cell derived from blood monocytes, resident in most tissues but able to roam. It has both scavenger and antigen-presenting functions in immune responses. // Large mononuclear phagocytic cells present in most tissues that have many functions, such as scavenger cells, pathogen-recognition cells, production of pro-inflammatory cytokines. Macrophages arise both embryonically and from bone marrow precursors throughout life.

Question 80

meiosis

Answer 80

A type of cell division in which diploid cells give rise to haploid cells destined to become gametes or spores. // Sex cell division that produces gametes, each with a haploid number of chromosomes. // A eukaryotic cell replication process that results in cells with half the chromosome number of the original cell. // The process by which the chromosome number of a reproductive cell becomes reduced to half the diploid (2n) or somatic number; results in the formation of gametes in animals or of spores in plants; important source of variability through recombination.

Question 81

membrane potential (Vm)

Answer 81

Difference in charges across the plasma membrane. // The voltage across a cell membrane; represented by the symbol Vₘ. // Voltage difference across a membrane due to a slight excess of positive ions on one side and of negative ions on the other. A typical membrane potential for an animal cell plasma membrane is –60 mV (inside negative relative to the surrounding fluid). // The difference in electrical potential across a biological membrane, commonly measured by the insertion of a microelectrode. Typical membrane potentials vary from 225 mV (by convention, the negative sign indicates that the inside is negative relative to the outside) to greater than 2100 mV across some plant vacuolar membranes.

Question 82

metastasis

Answer 82

The movement or spread of malignant cells from one part of the body to another. // Spread of a tumor from its original location to distant organs of the body by traveling through the blood or lymphatics or by direct extension. // The spread of cancer cells to previously unaffected organs. // The spread of cancer cells from their site of origin to other sites in the body.

Question 83

microRNA (miRNA)

Answer 83

A class of small RNA molecules (20 to 25 nucleotides after processing is complete) involved in gene silencing by inhibiting translation and/or promoting the degradation of particular mRNAs. // Small, single-stranded RNA that prevent translation of a complementary mRNA. // Short (about 22 nucleotides) RNA molecules present in eukaryotic cells. They act as posttranscriptional regulators mostly via degradation of target mRNAs or inhibition of their translation. // Short (~21 nucleotide) eukaryotic RNAs, produced by the processing of specialized RNA transcripts coded in the genome, that regulate gene expression through base-pairing with mRNA.

Question 84

mismatch repair

Answer 84

An enzymatic system for repairing base mismatches in DNA. // DNA repair processes that correct base pairs that are not properly hydrogen-bonded. // A repair system that corrects replication errors. // A type of DNA repair that causes mutations and is involved in somatic hypermutation and class switching in B cells.

Question 85

missense mutation

Answer 85

A mutation that changes a codon specifying an amino acid to a codon specifying a different amino acid. // A change in a single nucleotide or codon that results in the production of a protein with a single amino acid substitution. (Chapter 3) // A mutation that results in the substitution of an amino acid in a protein. // Mutation leading to a single amino acid substitution.

Question 86

mole (mol)

Answer 86

One gram molecular weight of a compound. See also Avogadro’s number. // Unit composed of 6.023 × 10 23 particles; its mass in grams is equal to the element’s atomic mass or the molecule’s molecular mass. // An amount of a chemical equal to the atomic masses of all the atoms in a molecule of the chemical. // A unit defined as the amount of material containing 6.0221421 * 10²³ particles (Avogadro’s number of particles).

Question 87

molecule

Answer 87

A chemical structure composed of covalently bonded atoms. // A combination of atoms forming a specific chemical compound. // A neutral collection of atoms held together by covalent bonds. // Two or more atoms joined chemically in a specific geometrical arrangement.

Question 88

monocyte

Answer 88

White blood cell that develops into a macrophage and phagocytizes bacteria and viruses. // A leukocyte that is the precursor of a macrophage. // Type of white blood cell with a bean-shaped nucleus; it is a precursor of tissue macrophages. // Type of white blood cell that leaves the bloodstream and matures into a macrophage in tissues.

Question 89

motor unit

Answer 89

One alpha motor neuron and all the skeletal muscle fibers it innervates. // One motor neuron and all the skeletal muscle fibers it innervates. // The combination of a motor neuron and all of the muscle fibers it innervates. // The motor nerve and all of the muscle fibers it innervates.

Question 90

mutualism

Answer 90

A symbiotic relationship between two organisms in which both benefit, such as the relationship between a human and its normal resident (commensal) gut microorganisms. // Ecological relationship between microbes and their host in which both the microbe and host benefit. // A type of symbiosis in which both organisms or populations are benefited. // An interaction between different species that is mutually beneficial.

Question 91

natural killer cell (NK cell)

Answer 91

A lymphoid cell that destroys tumor cells and virus-infected cells. // A type of ILC that is important in innate immunity to viruses and other intracellular pathogens, and in antibody-dependent cell-mediated cytotoxicity (ADCC). NK cells express activating and inhibitory receptors, but not the antigen-specific receptors of T or B cells. // (NK cell) An abundant lymphocyte population that comprises large, granular cells; distinguished from other lymphocytes by the absence of B and T cell antigen receptors; these cells are part of the innate defense system. Also called NK cells. ( Chapter 3) // Cytotoxic cell of the innate immune system that can kill virus-infected cells and some cancer cells.

Question 92

negative (indirect) selection

Answer 92

The process of identifying mutations by selecting cells that do not grow using replica plating. // Process by which thymocytes expressing a T cell receptor with high affinity for a self peptide bound to a self-MHC protein are eliminated by undergoing apoptosis.// The process by which self-reactive thymocytes are deleted from the repertoire during T-cell development in the thymus. Autoreactive B cells undergo a similar process in bone marrow. // (re: T cells) Elimination of T cells that recognize target cells that display “self ” peptides on their surfaces. (Chapter 4)

Question 93

neutrophil

Answer 93

The most common of the white blood cells. Cells that phagocytize bacteria. // A highly phagocytic granulocyte; also called polymorphonuclear leukocyte (PMN) or polymorph. // The most numerous type of white blood cell in human peripheral blood. Neutrophils are phagocytic cells with a multilobed nucleus and granules that stain with neutral stains. They enter infected tissues and engulf and kill extracellular pathogens. // White blood cell that is specialized for the uptake of particulate material by phagocytosis. Enters tissues that become infected or inflamed.

Question 94

nitric oxide (NO)

Answer 94

A reactive molecular gas species produced by cells— particularly macrophages—during infection, that is toxic to bacteria and intracellular microbes. // A gas produced from the amino acid arginine that serves as an intercellular messenger. // An unstable, diffusible messenger molecule produced in endothelial cells and some other tissues. // Gaseous signal molecule that is widely used in cell–cell communication in both animals and plants.

Question 95

nitrogen fixation

Answer 95

Conversion of atmospheric nitrogen (N2) into a reduced, biologically available form by nitrogen-fixing organisms. // Assimilation of atmospheric N2 into organic compounds. // Biochemical process carried out by certain bacteria that reduces atmospheric nitrogen (N2) to ammonia, leading eventually to various nitrogen-containing metabolites. // The conversion of nitrogen (N2) into ammonia.

Question 96

Nucleotide excision repair

Answer 96

A DNA repair system for bulky lesions. // The removal of relatively large defects such as thymine dimers in DNA via the excision of a segment of the DNA strand spanning the defect and repair synthesis by a DNA polymerase using the complementary strand as template. // The repair of DNA involving removal of defective nucleotides and replacement with functional ones. // Type of DNA repair that corrects damage of the DNA double helix, such as that caused by chemicals or UV light, by cutting out the damaged region on one strand and resynthesizing it using the undamaged strand as template. Compare base excision repair.

Question 97

Okazaki fragments

Answer 97

Short (100–200 nucleotides) DNA segments elongated from RNA primers during discontinuous synthesis of the lagging strand at a replication fork. (Chapter 9) // Pieces of DNA synthesized in the lagging strand during DNA replication. // Short segments of a DNA lagging strand that is biosynthesized discontinuously and then linked by DNA ligases. // Short strands of DNA made by copying the lagging strand during DNA synthesis.

Question 98

oligosaccharide

Answer 98

A carbohydrate consisting of 2 to approximately 20 monosaccharides. // Several monosaccharide groups joined by glycosidic bonds. // A short linear or branched chain of sugar residues (monosaccharides); also called a glycan. (Chapter 4) // Short, indigestible chain of monosaccharides, found mostly in legumes.

Question 99

operator

Answer 99

A region of DNA that interacts with a repressor protein to control the expression of a gene or group of genes. // A part of an operon that controls the expression of one or more structural genes by serving as the binding site for one or more regulatory proteins. // A repressor-binding regulatory DNA sequence in bacterial operons. // The region of DNA adjacent to structural genes that controls their transcription.

Question 100

operon

Answer 100

A unit of genetic expression consisting of one or more related genes and the operator and promoter sequences that regulate their transcription. // The operator and promoter sites and structural genes they control. // The unit of promoter, operator, and structural genes in bacteria. // A group of genes making up a regulatory or control unit. The unit includes an operator, a promoter, and structural genes.

Question 101

osmosis

Answer 101

Bulk flow of water through a semipermeable membrane into another aqueous compartment containing solute at a higher concentration. // Process by which water moves through a semipermeable membrane from a an area of higher to lower water concentration. // The flow of solvent from a solution of lower solute concentration to one of higher solute concentration. // The net movement of solvent molecules across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Question 102

osmotic pressure

Answer 102

Pressure generated by the osmotic flow of water through a semipermeable membrane into an aqueous compartment containing solute at a higher concentration. // The pressure required to stop osmotic flow. // Pressure exerted by water movement across a membrane as it moves toward an area of lower water concentration. // The force with which a solvent moves from a solution of lower solute concentration to a solution of higher solute concentration.

Question 103

Partition coefficient (P)

Answer 103

Pressure exerted by a gas in a mixture of gases. // The pressure due to any individual component in a gas mixture. // A constant that expresses the ratio in which a given solute will be partitioned or distributed between two given immiscible liquids at equilibrium. passive transport Diffusion of a polar substance across a biological membrane through a protein transporter; also called facilitated diffusion. // This is a measure of the distribution of molecules between two phases. For transdermal drug delivery studies, a partition coefficient (usually expressed as log10 value, hence ‘log P’) between octanol and water is often used as a guide to how well a molecule will distribute between the stratum corneum lipids and water. In some texts, the symbol K is used for the partition coefficient; here, and to avoid confusion with the permeability coefficient (kp), the symbol P (also widely used in the literature) has been employed.

Question 104

peptidoglycan

Answer 104

A component of bacterial cell walls that is recognized by certain receptors of the innate immune system. // A major component of bacterial cell walls; generally consists of parallel heteropolysaccharides cross-linked by short peptides. // The major bacterial cell wall polysaccharide. // The structural molecule of bacterial cell walls consisting of the molecules N-acetylglucosamine, N-acetylmuramic acid, tetrapeptide side chain, and peptide side chain.

Question 105

pH

Answer 105

Value indicating the relative hydrogen ion (H+) concentration of a solution; expressed as a number between 0 and 14. // The negative log of the concentration of H3O+ in a solution; the pH scale is a compact way to specify the acidity of a solution. // The negative logarithm of the hydrogen ion concentration of an aqueous solution. // The symbol for hydrogen ion (H1) concentration; a measure of the relative acidity or alkalinity of a solution.

Question 106

pinocytosis

Answer 106

A form of endocytosis by which cells ingest liquid; “cell drinking.” // Taking in molecules by infolding of the plasma membrane, in eukaryotes. // Literally, “cell drinking.” Type of endocytosis in which soluble materials are continually taken up from the environment in small vesicles and moved into endosomes along with the membrane-bound molecules. Compare phagocytosis. // Nonselective uptake of fluid droplets into the cell.

Question 107

plasma (cytoplasmic) membrane

Answer 107

The selectively permeable membrane enclosing the cytoplasm of a cell; the outer layer in animal cells, internal to the cell wall in other organisms. // Barrier separating the cytoplasm from the interstitial fluid. // The exterior membrane surrounding the cytoplasm of a cell. // The membrane that surrounds a living cell.

Question 108

pluripotent

Answer 108

Describes a cell that has the potential to give rise to all or almost all of the cell types of the adult body. // A cell that can differentiate into many different types of tissue cells. // An adjective applied to cells that have the potential to differentiate into many different types. // Typically referring to the capacity of a progenitor cell to generate all possible lineages of an organ system.

Question 109

Poly(A) tail (mRNA)

Answer 109

A structure at the 3′ end of eukaryotic messenger RNA. // A length of adenosine residues added to the 3’ end of many mRNAs in eukaryotes (and sometimes in bacteria). // The segment of 200 A residues present at the 3’ ends of most cellular and many viral mRNAs. (Chapters 10 and 11) // A polyadenosine tract 20 to 200 nucleotides long that is added to the 3′ ends of most eukaryotic mRNAs postranscriptionally.

Question 110

prophage (provirus)

Answer 110

Bacteriophage DNA that has been integrated into the host-cell chromosome. // Phage DNA inserted into the host cell’s DNA. // The genome of the quiescent bacteriophage in a lysogenic bacterium. (Chapter 1) // The genome of a temperate bacteriophage integrated into the chromosome of a lysogenic bacterium and replicated along with the host chromosome.

Question 111

protein kinase

Answer 111

A class of enzyme that phosphorylates proteins, a reaction that changes the conformation of the protein and its biological activity. // Enzyme that transfers the terminal phosphate group of ATP to one or more specific amino acids (serine, threonine, or tyrosine) of a target protein. // Enzymes that transfer the terminal phosphoryl group of ATP or another nucleoside triphosphate to a Ser, Thr, Tyr, Asp, or His side chain in a target protein, thereby regulating the activity or other properties of that protein. // Enzymes that add phosphate groups to proteins at particular amino acid residues: tyrosine, threonine, or serine.

Question 112

protein phosphatase

Answer 112

An enzyme that removes phosphate groups from proteins. // Enzyme that catalyzes phosphate removal from amino acids of a target protein. // Enzymes that hydrolyze a phosphate ester or anhydride bond on a protein, releasing inorganic phosphate, Pi. // Enzymes that remove phosphate groups from proteins phosphorylated on tyrosine, threonine, or serine residues by protein kinases.

Question 113

proteoglycan

Answer 113

Molecule consisting of one or more glycosaminoglycan chains attached to a core protein. // A hybrid macromolecule consisting of a heteropolysaccharide joined to a polypeptide; the polysaccharide is the major component. // Proteins linked to glycosaminoglycans, which are unbranched polysaccharides made of repeating disaccharides. (Chapter 2) // Products consisting of core protein and covalently bound sulfated glycosaminoglycans (GAGs).

Question 114

proto-oncogene

Answer 114

A normal cellular gene that can be changed to an oncogene by mutation. // A normal cellular gene that, when altered by mutation or misregulation, can contribute to cancer; thereafter called a cellular oncogene (c-oncogene). (Chapter 6) // Normal gene, usually concerned with the regulation of cell proliferation, that can be converted into a cancer-promoting oncogene by mutation. // A cellular gene, usually encoding a regulatory protein, that can be converted into an oncogene by mutation.

Question 115

proton

Answer 115

Subatomic particle with a positive charge; found in the nucleus of an atom. // A positively charged particle in the nucleus of an atom. // A positively charged subatomic particle found in the nucleus of an atom. // Positively charged subatomic particle that forms part of an atomic nucleus. Hydrogen has a nucleus composed of a single proton (H+).

Question 116

pseudogene

Answer 116

Nucleotide sequence of DNA that has accumulated multiple mutations that have rendered an ancestral gene inactive and nonfunctional. // An inactive but stable component of a genome resembling a gene; apparently derived from active genes by mutation. // Degenerate, nonfunctional gene that is related to a functional gene. // Gene elements that have lost the ability to encode a functional protein but that are retained in the genome and may continue to be transcribed normally.

Question 117

Ras (Ras protein)

Answer 117

A (proto)oncogene coding for the Ras protein, a membrane-associated, mitogen-activated G protein. // A small family of proto-oncogenes that are frequently mutated in cancers, each of which produces a Ras monomeric GTPase. // A small GTPase with important roles in intracellular signaling pathways, including those from lymphocyte antigen receptors. // Monomeric GTPase of the Ras superfamily that helps to relay signals from cell-surface receptor tyrosine kinase receptors to the nucleus, frequently in response to signals that stimulate cell division. Named for the ras gene, first identified in viruses that cause rat sarcomas.

Question 118

rate constant (k)

Answer 118

A measure for the rate of a reaction. // The constant k in a rate equation. // The proportionality constant that relates the velocity of a chemical reaction to the concentration(s) of the reactant(s). // A constant of proportionality in the rate law.A constant of proportionality in the rate law.

Question 119

reading frame

Answer 119

The phase in which nucleotides are read in sets of three to encode a protein. An mRNA molecule can be read in any one of three reading frames, only one of which will give the required protein. // A contiguous, nonoverlapping set of three-nucleotide codons in DNA or RNA. // The frame in which the codons on the messenger RNA are translated. // The series of nucleotide triplets that are sequentially positioned in the A site of the ribosome during translation of an mRNA; also, the sequence of nucleotide-pair triplets in DNA that correspond to these codons in mRNA.

Question 120

replication

Answer 120

Synthesis of daughter nucleic acid molecules identical to the parental nucleic acid. // A duplication process that is accomplished by copying from a template (for example, reproduction at the level of DNA). // Duplication of DNA prior to cell division. // The process by which double-stranded DNA uncoils and is replicated to produce two new copies.

Question 121

respiration

Answer 121

Any metabolic process that leads to the uptake of oxygen and the release of CO2. // A series of redox reactions in a membrane that generates ATP; the final electron acceptor is usually an inorganic molecule. // Movement of O2 and CO2 between air and systemic body cells. // Transfer of electrons from electron donors such as NADH via an electron transport chain to molecular oxygen or other final electron acceptors and concomitant generation of ATP. In eukaryotes respiration takes place in the mitochondria.

Question 122

sarcoplasmic reticulum (SR)

Answer 122

The endoplasmic reticulum of muscle cells, a specialized calcium-storage organelle. // An extensive, lattice-like, longitudinal network of tubules and structures that store Ca2+. // An organelle within a skeletal muscle fiber that stores Ca²⁺ and releases it when stimulated by an action potential in T tubules. // Endoplasmic reticulum found in muscle cells; stores calcium ions required for contraction.

Question 123

scaffold protein // scaffolding protein // scaffolds

Answer 123

Protein that binds groups of intracellular signaling proteins into a signaling complex, often anchoring the complex at a specific location in the cell. // Noncatalytic proteins that nucleate formation of multienzyme complexes by providing two or more specific binding sites for those proteins. // A viral protein that is required for assembly of an icosahedral protein shell but is absent from mature virions. (Chapter 13) // Adaptor-type proteins with multiple binding sites, which bring together specific proteins into a functional signaling complex.

Question 124

Small nuclear ribonucleoproteins (snRNPs, pronounced “snurps”)

Answer 124

Structures that contain small nuclear RNAs and several proteins; several participate in pre-mRNA splicing. (Chapter 10) // Components of the spliceosome. // RNA-protein complexes that are components of spliceosomes. // Small nuclear ribonucleoprotein (pronounced “snurp”). Short RNA transcript plus protein that combines with pre-mRNA to remove introns and join exons together.

Question 125

statin

Answer 125

A drug that controls cholesterol biosynthesis in the body by blocking the HMG-CoA reductase enzyme. // Any of a class of drugs used to reduce blood cholesterol in humans; act by inhibiting the enzyme HMG-CoA reductase, an early step in sterol synthesis. // Drug inhibitors of HMG-CoA reductase used to lower cholesterol. sterile injury Damage to tissues due to trauma, ischemia, metabolic stress, or autoimmunity, bearing many immune features similar to infection. sterilizing immunity An immune response that completely eliminates a pathogen. // Lipid-lowering drugs that inhibit 3-hydroxy-3- methylglutaryl-coenzme A (HMG-CoA) reductase.

Question 126

stereoisomers

Answer 126

Compounds that have the same composition and the same order of atomic connections but different molecular arrangements. // Isomers that have their atoms connected in the same order but have different three-dimensional arrangements. The term stereoisomer includes both enantiomers and diastereomers. // Molecules in which the atoms are bonded in the same order but have a different spatial arrangement. // Two molecules consisting of the same atoms, arranged in the same manner but differing in their relative positions; mirror images; also called d-isomer and l-isomer.

Question 127

superoxide dismutase (SOD)

Answer 127

An antioxidant enzyme that promotes the dismutation of superoxide into hydrogen peroxide and oxygen. It may contain a mineral, such as copper or manganese. // An enzyme that turns superoxide into oxygen and hydrogen peroxide. // An enzyme that converts the superoxide ion produced in the phagolysosome into hydrogen peroxide, a substrate for further reactive antimicrobial metabolites. // An enzyme that destroys superoxide.

Question 128

synapse

Answer 128

Communicating cell–cell junction that allows signals to pass from a nerve cell to another cell. In a chemical synapse, the signal is carried by a diffusible neurotransmitter. In an electrical synapse, a direct connection is made between the cytoplasms of the two cells via gap junctions. // (sin′aps) Functional contact of a neuron with another neuron or effector (muscle or gland). // The region of contact where a neuron transfers information to another cell. // The space between adjacent neurons (nerve cells) in which the impulse is transmitted from one neuron to another neuron.

Question 129

Terpenes/Terpenoids

Answer 129

MEP or MEV pathway derived isoprenoids associated with primary metabolism, plant communication and defense responses. // A class of chemical structures that function as pigments, vitamins, and precursors to sex hormones. Sometimes called isoprenoids. // A very large group of secondary metabolites including monoterpenes (with 10 carbons), sesquiterpenes (15 C), diterpenes (20 C), triterpenes (30 C), steroids (27 or less), tetraterpenes (40 C). // Lipids that are formally derived by head-to-tail polymerization of isoprene units.

Question 130

transamination

Answer 130

A biochemical reaction that transfers an amino group from one amino acid to an a-keto acid to produce a new amino acid, while producing a new a-keto acid with the remaining carbon skeleton of the original amino acid. // Enzymatic transfer of an amino group from an -amino acid to an -keto acid. // The exchange of an amino group and a keto group between reactants. // The transfer of an amino group from an amino acid to another organic acid.

Question 131

transcriptome

Answer 131

The complete set of RNAs transcribed from a genome. // The entire complement of RNA transcripts present in a given cell or tissue under specific conditions. // The entirety of all RNA molecules in a biological system (e.g., a cell) at a particular time. This includes the mRNA (messenger RNA) encoding for proteins as well as rRNA (ribosomal RNA), tRNA (transfer RNA), snRNA (small nuclear RNA), and other noncoding RNA. // The totality of RNAs transcribed in a particular cell at a particular time.

Question 132

transition state

Answer 132

An activated form of a molecule in which the molecule has undergone a partial chemical reaction; the highest point on the reaction coordinate. // Structure that forms transiently in the course of a chemical reaction and has the highest free energy of any reaction intermediate. Its formation is a rate-limiting step in the reaction. // The most unstable intermediate in a chemical reaction. // An activated complex between reactants, representing the highest energy point on a reaction curve. Transition states are unstable complexes that can’t be isolated.

Question 133

Tropism

Answer 133

Directional growth in response to stimulation. Tropisms can be positive (growth toward the direction of the stimulus) or negative (growth away from the stumulus). Examples include gravitropisms (growth dependent on gravity) and phototropism (growth dependent on light). // Th e predilection of a virus to invade, and reproduce, in a particular cell type. (Chapter 2) // The characteristic of a pathogen that describes the cell types it will infect. // The predilection of a virus to invade, and reproduce, in a particular cell type. (Chapter 5)

Question 134

turnover number

Answer 134

The number of times an enzyme molecule transforms a substrate molecule per unit time, under conditions giving maximal activity at substrate concentrations that are saturating. // The number of substrate molecules acted on per enzyme molecule per second. // The number of substrate molecules acted on by an enzyme molecule per unit time. // The number of substrate molecules converted to product by one enzyme molecule per second.

Question 135

ultraviolet (UV) radiation // UV light

Answer 135

Electromagnetic radiation in the region of 200 to 400 nm. // Electromagnetic radiation with slightly smaller wavelengths than visible light. // The portion of the electromagnetic spectrum—wavelengths from about 1 to 350 nm—between ionizing radiation and visible light. UV is absorbed by DNA and is highly mutagenic to unicellular organisms and to the epidermal cells of multicellular organisms. // Electromagnetic radiation with wavelength between 380 and 100 nm; the UV-A (380 to 315 nm) and UV-B (315–280 nm) can reach Earth’s surface and cause damage to biological molecules.

Question 136

vector

Answer 136

A DNA molecule known to replicate autonomously in a host cell, to which a segment of DNA may be spliced to allow its replication; for example, a plasmid or an artificial chromosome. // (1) A plasmid or virus used in genetic engineering to insert genes into a cell. (2) An arthropod that carries disease-causing organisms from one host to another. // A carrier, oft en an arthropod, that transmits a virus or other infectious agent from one host to another. (Chapter 1) // A plasmid or viral chromosome that may be used to construct recombinant DNA molecules for introduction into living cells.

Question 137

zygote

Answer 137

Diploid cell produced by fusion of a male and female gamete. A fertilized egg. // (zı̄′gōt) Diploid cell resulting from the union of a sperm and an ovum. // A diploid cell produced by the fusion of two haploid gametes. // The cell produced by the union of two mature sex cells (gametes) in reproduction; also used in genetics to designate the individual developing from such a cell.