生物化学英文版练习题及答案.doc

Glossary for BiochemistryAacetyl CoA carboxylase An enzyme that catalyzes the ATP-dependent synthesis of malonyl CoA from acetyl CoA and carbon dioxide, the committed step in fatty acid synthesis.acetylcholine A common neurotransmitter that exerts its effects by first binding to the acetylcholine receptor.acetylcholine receptor A ligand-gated channel that promotes a large inward current of sodium ions and triggers an action potential; composed of a pentamer of four kinds of polypeptide subunits, the channel opens to allow passage of sodium and potassium ions when two acetylcholine molecules promote transient opening of the channel.activated carriers Small molecules carrying activated functional groups that can be donated to other molecules; for instance, ATP carries activated phosphate groups and CoA carries activated acyl groups.activation domain The structural region of a transcription factor that facilitates transcription in some manner. See also DNA-binding domain.active site A specific region of an enzyme that binds the substrate and carries out catalysis.active transport The transport of an ion or a molecule against a concentration gradient, where DG for the transported species is positive; the process must be coupled to an input of free energy from a source such as ATP, an electrochemical gradient of Na+ or K+, or light.acyl adenylate A mixed anhydride in which the carboxyl group of a molecule is linked to the phosphoryl group of AMP; the formation of acyl adenylates is a means of activating carboxyl groups in biochemical reactions, such as the formation of fatty acyl CoA molecules from a free fatty acid and coenzyme A.acyl carrier protein (ACP) A bacterial polypeptide that is linked to phosphopantetheine and acts as a carrier of the growing fatty acyl chain during fatty acid biosynthesis.addition to or formation of double bond A reaction in which a functional group is added to a double bond or a group is removed from a molecule to form a double bond.adenylate cyclase An enzyme that generates cAMP, a second messenger, from ATP.adipocytes Mammalian cells that are the major storage site for bic glycolysis The use of lactic acid fermentation to generate ATP even the presence of enough oxygen to support cellular bic In the presence of oxygen.affinity chromatography A protein-purification technique based on the high affinity of many proteins for specific chemical groups. Such groups are attached to an inert matrix, and the protein sample is applied; only those proteins with an affinity for the groups will bind.affinity labeling A means of mapping the active site of an enzyme by using a substrate analog that binds to the active site and forms a covalent bond with a nearby amino acid.agonists Molecules that bind to receptor proteins and trigger signaling pathways.alcoholic fermentation The anaerobic conversion of glucose into ethanol with the concomitant production of ATP.aldolase An enzyme that cleaves an aldol. Aldolases are important in carbohydrate metabolism.aldose A monosaccharide whose C-1 carbon atom contains an aldehyde group.allosteric interaction An interaction between a small molecule (a ligand) and a site on a protein that may be some distance away from the active site; the interaction causes a conformational change and consequent alteration in the catalytic activity of the protein. helix A common structural motif in proteins, in which a polypeptide main chain forms the inner part of a right-handed helix, with the side chains extending outward; the helix is stabilized by intrachain hydrogen bonds between NH and CO groups of the main chain.-ketoglutarate dehydrogenase A citric acid cycle enzyme that catalyzes the oxidative decarboxylation of -ketoglutarate to yield succinyl CoA. This enzyme, which helps to regulate the rate of the citric acid cycle, is structurally and mechanistically similar to the pyruvate dehydrogenase complex.-amylase A hydrolytic enzyme that cleaves the a -1,4 bonds of starch and glycogen, but not the a -1,6 bonds.Ames test A simple, rapid means of detecting carcinogens by measuring a chemicals ability to induce mutations in Salmonella bacteria.amiloride-sensitive sodium channel A sodium channel important in the detection of the taste of salt. Such channels are inhibited by amiloride, which also mutes the taste of salt.amino acid An organic acid with an -carbon atom linked to a carboxylic acid, an amino group, a hydrogen atom, and a side chain (the R group). Twenty different amino acids are the building blocks of proteins.amino sugar A sugar that contains an amino group rather than a hydroxyl group at the C-2 position; the most common amino sugars are glucosamine and galactosamine.aminoacyl-tRNA An amino acid ester of transfer RNA.aminoacyl-tRNA synthetase An enzyme that activates an amino acid and then links it to transfer RNA. Also known as an activating enzyme, each aminoacyl-tRNA synthetase is specific for a particular amino acid.aminotransferase (transaminase) A class of enzymes that transfer an -amino group from an -amino acid to an - keto acid. Also called transaminases.ampere A measure of electrical current: the flow of 6.24 1018 charges per second.amphipathic molecule A molecule, such as a membrane lipid, that contains both a hydrophobic and a hydrophilic moiety.amylopectin The branched form of starch, containing glucose residues in about one -1,6 linkage per thirty -1,4 linkages.amylose The unbranched form of starch, containing glucose residues in -1,4 linkage.anabolism The set of metabolic reactions that require energy to syntheize molecules from simpler precursors.anaerobic In the absence of oxygen.anaplerotic reaction From the Greek for fill up, referring to a reaction that replenishes intermediates removed from a metabolic pathway. The most common example is the reaction catalyzed by pyruvate carboxylase, in which the carboxylation of pyruvate produces oxaloacetate, a key component of the citric acid cycle.anion exchange Ion-exchange chromatography in which a protein mixture is passed through a column containing a matrix bearing positive charges. Proteins bearing negative charges will bind to the column while those with positive charges will pass through the column.anomers Isomers of cyclic hemiacetals or hemiketals, with different configurations only at the carbonyl carbon atom; that carbon is known as the anomeric carbon.antagonist A molecule that binds to a receptor protein but does not trigger the signaling pathway. Such molecules are like competitive inhibitors for enzymes.antibody A protein synthesized by an animal in response to the presence of a foreign substance, or antigen; often binds to the antigen, neutralizing it or marking it for destruction.anticodon Three-nucleotide sequence of tRNA that base-pairs with a codon in mRNA.antigen A foreign substance that elicits the synthesis of an antibody.antigenic determinant Site on an antigen to which an antibody binds. Also called an epitope.antigenic determinant The specific site on an antigen that is recognized by an antibody. Also known as an epitope.antimycin A An antibiotic from Streptomyces that inhibits the respiratory chain by blocking electron transfer in the cytochrome reductase complex.antiserum Serum prepared from the blood of an immunized animal containing soluble antibodies specific for a particular antigen.apoptosis A cascade of proteolytic enzymes that results in controlled cell death in response to significant cell damage or specific developmental programs. Also called programmed cell death.Archaea The domain of life that comprises single cell organisms lacking a nucleus. Formerly believed to be member of the domain Bacteria, Archaea are now known to have a unique evolutionary history with biochemical characteristics different from the other two domains of life.ascorbate (vitamin C) A water-soluble vitamin that functions as an antioxidant and is required for the hydroxylation of collagen; scurvy results if ascorbate is deficient.assay A test for some unique identifying property of a protein to be purified.ATP (adenosine 5-triphosphate) A nucleotide consisting of adenine, ribose, and triphosphate units that serves as the cellular energy currency.ATP synthase Molecular assembly of the inner mitochondrial membrane responsible for the respiratory-chain-driven synthesis of ATP. Also called Complex V, mitochondrial ATPase, H+-ATPase, or F0F1-ATPase.ATPase Enzymes that catalyze the hydrolysis of adenosine triphosphate (ATP) to form adenosine diphosphate (ADP) and inorganic phosphate (Pi) and use the energy released to power otherwise endergonic reactions.ATP-driven pump Membrane proteins that use the energy of ATP hydrolysis to drive the thermodynamically uphill transport of ions or molecules.autoradiography A means of detecting radioactive molecules immobilized in a separation medium such as polyacrylamide; the radioactivity of the molecules will blacken x-ray film.BBacteria The domain of life that comprises single cell organisms lacking a nucleus. Members of this domain differ evolutionarily and biochemically from the Archaea, with whom they were formerly grouped.bacterial artificial chromosome An artificial bacterial chromosome, a highly engineered version of the E. coli fertility (F factor), that can serve as a cloning vector for inserts as larges as 300 kb.bacteriorhodopsin A 26-kd integral membrane protein that absorbs light and converts its energy into proton-motive force, which is then used to synthesize ATP.ball-and-chain model A model for the regulation of the K+ channel that postulates that the first 20 residues of the K+ channel form a cytoplasmic unit (the ball) that is attached to a flexible segment of the polypeptide (the chain). When the channel is closed, the ball rotates freely in the aqueous solution. When the channel opens, the ball quickly finds a complementary site in the open pore and occludes it.basic-leucine zipper (bZip) protein A eukaryotic DNA binding unit that consists of a pair of long a helices. Because these pairs are often stabilized by appropriately spaced leucine residues, these structures are often referred to as leucine zippers.B-DNA helix A right-handed double helix with the following characteristics: the two strands are antiparallel; the bases are inside the helix and the phosphates and deoxyribose sugars are on the outside; adenine forms hydrogen bonds with thymine, and guanine forms them with cytosine; the bases in each pair are coplanar; there are 10.4 residues per turn, with a pitch of 35 . sheet A common structural motif in proteins, in which two or more strands are associated as stacks of chains, stabilized by interchain hydrogen bonds; a number of strands running in the same direction form a pleated sheet, whereas such strands running in opposite directions form an antiparallel pleated sheet.-galactosidase An essential enzyme in lactose metabolism that hydrolyzes lactose into galactose and glucose.bifunctional enzyme An enzyme with two different, often opposing, catalytic activities on one polypeptide chain. For instance, phosphofructokinase 2 synthesizes fructose 2,6-bisphosphate and fructose 2,6-bisphosphatase hydrolyzes it, yet both active sites are on the same polypeptide chain.bile salts Polar derivatives of cholesterol that are made in the liver, stored in the gall bladder, and released into the small intestine, where they act as detergents to solubilize dietary lipids, facilitating their digestion and absorption.biological macromolecule Large molecules such as proteins and nucleic acids, that are key functional and structural components of living systems.biotin A vitamin that plays a role in carboxylation and decarboxylation reactions.2,3-bisphosphoglycerate An allosteric effector of hemoglobin that decreases the affinity of hemoglobin for oxygen.bloodbrain barrier The tight junctions between endothelial cells that line blood vessels within the brain and spinal cord.body mass index (BMI) A value, calculated by dividing a persons weight in pounds (kg) by (height in inches (cm)2, that is a reliable indicator of obesity for most people.Bohr effect The observation made by Christian Bohr that H+ and CO2 promote the release of oxygen from oxyhemoglobin.bongkrekic acid An antibiotic that inhibits the action of ATP-ADP translocase.buffer An aqueous solution consisting of a weak acid and it conjugate base (or vice versa) that resists changes in pH when strong acids or bases are added.CC3 plant A plants that lacks the C4 pathway.C4 pathway A means by which four-carbon compounds, such as oxaloacetate and malate, carry carbon dioxide from mesophyll cells in contact with the air to bundle-sheath cells, which are the major sites of photosynthesis. The pathway accelerates photosynthesis by concentrating carbon dioxide in photosynthetic cells.C4 plant A plant that utilizes the C4 pathway.CAAT box A component of many eukaryotic promoters with the consensus sequence 5-GNCAATCT- 3.calorie The amount of heat required to raise the temperature of 1 gram of water from 14.5C to 15.5C.Calvin cycle (Dark reactions) In plants, a cyclic metabolic pathway in which carbon dioxide is incorporated into ribulose 1,5-bisphosphate to give compounds that can be used for the synthesis of glucose.5 cap A structure at the 5 end of eukaryotic mRNA that stabilizes the mRNA and enhances its translation. The cap contains a 7-methyl guanylate residue attached by a triphosphate linkage to the sugar at the 5 end of the mRNA in a rare 5-5 linkage.carbohydrates Saccharides, which are aldehyde or ketone compounds with multiple hydroxyl groups. Also defined as organic compounds with the empirical formula (CH2O)n.carbon monoxide CO; A colorless, odorless gas that binds to hemoglobin at the same site as oxygen and thereby prevents oxygen binding.carbonic anhydrase An enzyme that catalyzes the reaction of carbon dioxide with water to form carbonic acid.carbonium ion A carbon compound that contains a positively charged carbon atom; a carbonium atom is critical for catalysis by lysozymecarboxyhemoglobin A complex of carbon monoxide and hemoglobin that does not bind oxygen.carboxylase An enzyme that catalyzes a carboxyl transfer reaction; biotin is usually required as a coenzyme.carnitine A zwitterionic compound formed from lysine that acts as a carrier of long-chain fatty acids from the cytosol to the mitochondrial matrix.cascade, enzymatic A sequence of reactions, in which at each step a product stimulates an ensuing reaction, generating an amplification of a relatively small stimulus or signal.catabolism The set of metabolic reactions that transform fuels into cellular energy.catabolite activator protein (CAP) The cAMP response protein; when bound to cAMP, CAP binds to an inverted repeated of the lac operon, near position -61 relative to the start site of transcription, to stimulate transcription.catabolite repression The repression by glucose of catabolic enzymes required for the catabolism of carbohydrates other than glucose.catalase A ubiquitous heme protein that catalyzes the dismutation of hydrogen peroxide into molecular oxygen and water.catalysis by approximation Enhancing the rate of a reaction by bringing multiple substrates together along a single binding surface of an enzyme.catalytic antibodies Antibodies generated by using transition-state analogs of a particular reaction as antigens. Such antibodies often function as catalysts for the reaction. Also called abzymes.catalytic group An amino acid or cofactor at an enzymes active site that directly participates in the making or breaking of covalent bonds.catalytic RNA One of a class of RNA molecules that display enzymatic activity.catalytic triad A constellation of three residues, found in many proteolytic enzymes, in which two of the residues convert the remaining residue, usually a serine or cysteine, into a potent nucleophile.cation exchange Ion-exchange chromatography in which a protein mixture is passed through a column containing a matrix bearing negative charges. Proteins bearing positive charges will bind to the column while those with negative charges will pass through the column.CD4 A protein present on the surface of helper T cells that, along with the T-cell receptor, binds to class II MHC proteins on antigen-presenting cells. CD4 is the source of the specificity of helper T cells for class II MHC interactions.cDNA library A collection of all of the complementary DNA for all mRNA that a cell contains, which have been inserted into vectors, and then inserted into bacteria. CDP-alcohol Activated form of an alcohol that can be used in the synthesis of phosphoglycerides by combining with diacylglycerol at the free hydroxyl group on glycerol; for instance, CDP-choline can react with diacylglycerol to form the phospholipid phosphatidylcholine.CDP-diacylglycerol (cytidine diphosphodiacylglycerol) Formed from phosphatidate and cytidine triphosphate (CTP); activated diacylglycerol used in the synthesis of phosphoglycerides such as phosphatidyl serine.cell cycle The coordination of DNA replication and cell division in eukaryotes. Mitosis takes place only after DNA synthesis. Two gaps (G1 and G2) in time separate the two processes.cellular respiration The generation of high-transfer-potential electrons by the citric acid cycle, their flow through the respiratory chain to O2, and the accompanying synthesis of ATP.cellulose An unbranched homopolysaccharide in plants, composed of glucose residues in -1,4 linkage; the major structural polysaccharide in plants.ceramide (N-acyl sphingosine) A sphingosine with a long-chain acyl group attached to the amino group.cerebroside A sph