生化英文习题.doc

八年制复习资料一Question1. While studying the structure of a small gene that was recently sequenced during the Human Genome Project, an investigator notices that one strand of the DNA molecule contains 20 As, 25 Gs, 30 Cs, and 22 Ts. How many of each base is found in the complete double-stranded molecule?A. A = 40, G = 50, C = 60,T = 44B. A = 44, G = 60, C = 50,T = 40C. A = 45, G = 45, C = 52,T = 52D. A = 50, G = 47, C = 50,T = 47E. A = 42, G = 55, C = 55,T = 422. The base sequence of the strand of DNA used as the template for transcription has the base sequence GATCTAC. What is the base sequence of the RNA product? (All sequences are written according to standard convention.)A. CTAGATGB. GTAGATCC. GAUCUACD. CUAGAUGE. GUAGAUC3. A four-year-old child who becomes easily tired and has trouble walking is diagnosed with Duchenne muscular dystrophy, an X-linked recessive disorder. Genetic analysis shows that the patients gene for the muscle protein dystrophin contains a mutation in its promoter region. What would be the most likely effect of this mutation?A. Initialtion of dystrophin transcription will be deficient.B. Termination of dystrophin transcription will be deficient.C. Capping of dystrophin mRNA will be defective.D. Splicing of dystrophin mRNA will be defective.E. Tailing of dystrophin mRNA will be defective.AnswerE. the two DNA strands are complementary to each other, with A base-paired with T, and G base paired with C. So, for example, the 20 As on the first strand would be paired with 20 Ts on the second strand, the 25 Gs on the first strand would be paired with 25 Cs on the second strand, and so forth. When these are all added together, the correct numbers of each base are indicated in choice G. Notice that, in the correct answer, A=T and G=CE. All sequences are written in the standard convention (5-3). The RNA product has a sequence that is complementary to the sequence of the template strand of DNA. Uracil (U) is found in RNA in place of the thymine (T) in DNA. Thus, the DNA template 5-GATCTAC-3 would produce the RNA product 3-CUAGAUG-5 or, written correctly in the standard direction, 5-GUAGAUC-3.A. Mutations in the promoter prevent formation of the RNA polymerase II transcription complex, and the initation of mRNA synthesis will be greatly decreased. A deficiency of dystrophin mRNA will result in a deficiency in the procduction of the dystrophin protein,Which one of the following corredtly pairs an amino acid with a valid chemical characteristic?A. Glutamine: Contains a hydroxyl group in tis side chainB. Serine: Can form disulfide bondsC. Cysteine: Contains the smallest side chainD. Isoleucine: is nearly always found buried in the center of proteinsE. Glycine: Contains an aminde group in its side chainWhich one of the following statements concerning glutamine is correct?A. Contains three titratalbe groupsB. Is classified as an acidic amino acidC. Contains an amide groupD. Has E as its one-letter symbolE. Migrates to the cathode (negative electrode ) during electrophoresis at pH 7.0A peptide bond:A. has a partial double-bond character.B. is ionized at physiologic pHC. is cleaved by agents that denature proteins, such as organic solvents an high concentrations of ureaD. is stale to heating in strong acidsE. occurs most commonly in the cis configuration.Which one of the following statements is correct?A. The -helix can be composed of more than one polypeptide chain.B. -sheets exist only in the antiparallel form.C. -Bends often contain proline.D. Motifs are a type of secondary structure.E. The -helix is stabilized primarily by ionic interactions between the side chains of amino acids.D. In proteins found in aqueous solutions, the side chains of the nonpolar amino acids, such isoleucine, tend to cluster together in the interior of the protein. Glutamine contains an amide in its side chain. Serine and threonine contain a hydroxyl group in their side chain. Cysteine can form disulfide bonds. Glycine contains the smallest side chain.C. Glutamine contains two titratable groups, -carboxyl and -amino. Glutamine is a polar, neutral amino acid that shows little electrophoretic migration at pH 7.0. The symbol for glutamine is “Q”.A. the peptide bond has a partial double-bond character. Unlike its components the -amino and -carboxyl groups the components of the peptide bond do not accept or give off protons. The peptide bond is not cleaved by organic solvents or urea, but is labile to strong acids. It is usually in the trans configurationC. -bends often contain proline, which provides a kink. The -helix differs from the -sheet in that it always involves the coiling of a single polypeptide chain. The -sheet occurs in both parallel and antiparallel forms. Motifs are elements of tertiary structure. The -helix is stabilized primarily by hydrogen bonds between the C=O and NH- groups of peptide bonds.Which one of the following statements about protein structure is correct?A. Proteins consisting of one polypeptide can have quaternary structure.B. The formation of a disulfide bond in a protein requires that the two participating cysteine residues be adjacent to each other in the primary sequence of the protein.C. The stbility of quaternary structure in proteins is mainly a result of covalent bonds among the subunits.D. the denaturation of proteins always leads to irreversible loss of secondary and tertiary structure.E. The information required for the correct folding of a protein is contained in the specific sequence of amino acids along the polypeptide chain.An 80-year-old man presented with impairment of higher intellecutual function and alterations in mood and behavior. His family reproted progressive disorientation and memory loss over the last six months. There is no family history of dementia. The patient was tentatively diagnosed with Alzeheimer disease. Which one of the following best describes the disease?A. It is associated with -amyloid - an abnormal protein with an altered amino acid sequence.B. It results from accumulation of denatured proteins that have random conformations.C. It is associated with the accumulation of amyloid precursor protein.D. It is associated with the accumulation of amyloid peptide aggregates.E. It is an environmentally produced disease uninfluenced by the genetics of the individual.A competitive inhibitor of an enzyme:A. increases Km without affecting VmaxB. dncreases Km without affecting VmaxC. increases Vmax without affecting KmD. dncreases Vmax without affecting Km E. dncreases both Km and VmaxE. The correct folding of a protein is guided by specific interactions among the side chains of the amnin acid residues of a polypeptide chain. The two cysteine residues that react to form the disulfide bond may be a freat distaqnce apart in the primary structure (or on separate polypeptides), but are brought into close proximity by the three-dimensional folding of the polypeptide chain. Denaturation may either be reversible or irreversible. Quaternary structure requires more than one polypeptide chain. These chains associate through noncovalent interactions.D. Alzheimer disease is associated with long, fibrillar protein assemblies consisting of -pleated sheets found in the brain and elsewhere. The disease is associated with abnormal processing of a normal protein. The accumulated altered protein occurs in a -pleated sheet configuration that is neurotoxic. The A amyloid that is deposited in the brain in Alzheimer disease is derived by proteolytic cleavages from the larger amyloid precursor protein -a single transmembrane protein expressed on the cell surface in the brain an other tissues. Most cases of Alzheimer disease are sporadic, although at least five to ten percent of cases are familial.A. In the presence of a competitive inhibitor, an enzyme appears to have a lower affinity for substrate, but as the substrate level is increased, the observed velocity approaches Vm.Which one of the following statements concerning the bingding of oxygen by hemoglobin is correct?A. The Bohr effect results in a lower affinity for oxygen at higher pH values.B. Carbon dioxide increases the oxygen affinity of hemoglobin by binding to the amino terminal groups of the polypeptide chains.C. The oxygen affinity of hemoglobin increases as the percent saturation increases.D. The hemoglobin tetramer binds four molecules of 2,3-BPG.E. Oxyhemoglobin and deoxyhemoglobin have the same affinity for protons (H+)The Michaelis constant, Km, is:A. numerically equl to 1/2 VmaxB. dependent on the enzyme concentrationC. independent of pHD. numerically equal to the substrate concentration thar gives half-maximal velocityE. increased in the presence of a noncompetitive inhibitorsWhich one of the following statements concerning the components of the electron transport chain is correct?A. All of the components of the electron transport chain are present in large, multisubunit protein complexes embedded in the inner mitochondrial membrane.B. Oxygen directly oxidizes cytochrome C.C. Succinate dehydrogenase directly reduces cytochrome C.D. The elecron transport chain contains some polypeptide chains coded for by the nuclear DNA and come coded for by mtDNAE. Cyanide inhibits electron folw, but not proton pumping or ATP synthesis.C. The binding of oxygen at one heme group increases the oxygen affinity of the remaining heme groups in the same molecule. Carbon dioxide decreases oxygen affinity because it lowers the pH; also bingding of carbon dioxide stabilizes the taut, deoxy form. Hemoglobin binds one molecule of 2,3-BPG. Deoxyhemoglobin has a greater affinity for protons and, therefor, is a weaker acid.D. Remember Km has the dimensions of concentration and is a characteristic of an enzyme under a given set of reaction conditions. Km does depend on the concentration of enzyme, but can vary with pH. A noncompetitive inhibitor decreases Vmax, but does not alter Km.D. Thirteen of the approximately 100 polypeptides required for oxidative phosphorylation are coded for by mitochondrial DNA, including the electron transport components cytochrome c and coenzyme Q. oxygen directly oxidizes cytochrome oxidase. Succinate dehydrogenase directly reduces FAD. Cyanide inhibits electron flow, proton pumping, and ATP synthesis.A muscle biopsy from a patient with the rare disorder, Luft disease, showed abnormally large mitochondria that containde packed cristae when examined in the electron microscope. Basal ATPase activity of the mitochodria was seven times greater than normal. From these and other data it was concluded that oxidation and phosphorylation were partially uncoupled. Which of the following statements about this patient is correct?A. The rate of electron transport is abnormally low.B. The proton gradient across the inner mitochondrial membrane is greater than normal.C. ATP levels in the mitochondria are greater than normal.D. Cyanide would not inhibit electron flow.E. The patient shows hypermetabolism and elevated core temperature.A young black man entered his physicians office complaining of bloating and diarrhea. His eyes were sunken and the physician noted additional signs of dehydration. The patients temperature was normal. He explained that the episode had occurred following a birthday party at which he had participated in an ice cream eating contest. The patient reproted prior episodes of a similar nature following ingestion of a signifficant amount of dairy products. This clinical picture is most probably due to a deficiency in:A. salivary -amylase.B. isomaltaseC. pancreatic -amylaseD. sucraseE. lactaseWhich one of the following statements concerning glycolysis correct?A. The conversion of glucose to lactate requires the presence of oxygen.B. Hexokinase is improtant in hepatic glucose metabolism only in the absorptive period following consumption of a carbohydrate-containing meal.C. Fructose 2,6-bisphosphate is a potent inhibitor of phosphofructokinase.D. The rate-limiting reactions are also the irreversible reaction.E. The conversion of glucose to lactate yields two ATP and two NADH.E. When phosphorylation is partially uncoupled from electron flow, one would expect a decrease in the proton gradient across the inner mitochondrial membrane and, hence, impaired ATP synthesis. In an attempt to compensate for this defect in energy capture, metabolism and electron flow to oxygen is increased, this hypermetabolism will be accompanied by elevated body temperature because the energy in fuels is largely wasted, appearing as heat. The electron transport chain will still be inhibited by cyanide.E. The physical symptoms suggest a deficiency in an enzyme responsible for carbohydrate degradation. The symptoms observed following the ingestion of dairy products suggest that the patient is deficient in lactase.D. Hexokinase, phosphofructokinase and pyruvate kinase are all irreversible and are the regulated steps in glycolysis. The conversion of glucose to lactate (anaerobic glycolysis) is a process that does not involve a net oxidation or reduction and, thus, oxygen is not required. Glucokinase (not hexokinase) is important in hepatic glucose metabolism only in the absorptive period following consumption of a carbohydrate-containing meal. Fructose 2,6-bisphosphate is a potent activator (not inhibitor) of phosphofructokinase. The conversion of glucose to lactate yields two ATP but not net production of NADH.The reaction catalyzed by phosphofructokinase:A. is activated by high concentrations of ATP and citrate.B. uses fructose 1-phosphate as substrate.C. is the regulated reaction of the glycolytic pathway.D. is near equilibrium in most tissues.E. is inhibited by fructose 2,6-bisphosphate.Compared with the resting state, vigorously contracting muscle shows:A. an increased conversion of pyruvate to lactate.B. decreased oxidation of pyruvate to CO2 and water.C. a decreased NADH/NAD+ ratio. D. a decreased concentration of AMP.E. decreased levels of 2,6-bisphosphate.A 43-year-old man presented with symptoms of weakness, fatigue, shortness of breath, and dizziness. His hemoglobin levels were between 5 to 7 g/dl (normal for a male being greater than 13.5 g/dl). Red blood cells isolated from the patient showed abnormally lov level of lactate production. A deficiency of which one of the following enzymes would be the most likely cause of this patients anemia.A. Phosphoglucose isomeraseB. phosphofructokinaseC. pyruvate kinase D. hexokinaseE. lactate dehydrogenaseThe conversion of pyruvate to acetyl CoA and CO2:A. is reversible.B. Involves the participation of lipoic acid.C. Is activated when pyruvate dehydrogenase complex is phosphorylated by a protein kinase in the presence of ATP.D. Occurs in the cytosol.E. Depends on the coenzyme biotin.Which one of the following is a condition decreased the oxidation of acetyl CoA by the citric acid cycle?A. A low ATP/ADP ratio B. A low NADH due to rapid oxidization to NAD+ through the respiratory chainC. A low NAD+/NADH ratioD. A high concentration of AMPE. A low GTP/GDP ratioC. Phosphofructokinase is the pace-setting enzyme of glycosis. It is inhibited by ATP and citrate, uses fructose 6-phosphate as substrate, and catalyzes a reaction that is far from equilibrium. The reaction is activated by fructose 2,6-bisphosphate.A. Vigorously contracting muscle shows an increased formation of lactate and an increased rate of pyruvate oxidation compared with resting skeletal muslce. The levels of AMP and NADH increase, whereas change in the concentration of fructose 2,6-bisphosphate is not a key regulatory factor in muscle.C. Decreased lactate production in the erythrocyte indicates a defect in glycolysis. Among patients exhibiting genetic defects of glycolytic enzymes, about 95 percent show a deficiency in pyruvate kinase, and four percent exhibit phosphoglucose isomerase deficiency. Pyruvate kinase deficiency is the second most common cause (after glucose-6-phosphate dehydrogenase deficiency) of enzyme deficiency-related hemolytic anemia.B. lipoic acid is an intermediate acceptor of the acetyl group formed in the reaction. Pyruvate dehydrogenase complex catalyzes an irreversible reaction that is inhibited when the enzyme is phosphorylated. The enzyme is located in the mitochondrial matrix.C. A low NAD+/NADH ratio ratio limits the rates of the NAD+-requiring dehydrogenases. A low ATP/ADP or GTP/GDP ratio stimulates the cycle. AMP does not directly affect the cycle.The following is the sum of three steps in the citric acid cycle:A + B + FAD + H2O C + FADH2 +NADH Reactant A Reactant B Reactant CA. Succinyl CoA GDP SuccinateB. Succinate NAD+ OxaloacetateC. Fumarate NAD+ OxaloacetateD. Succinate NAD+ MalateE. Fumarate GTP MalateA one-month-old male showed abnormalities of the nervous system and lactic acidosis. Enzyme assay for pyruvate dehydrogenase (PDH) activity on extracts of cultured skin fibroblasts showed five percent of normal activity, with a low concentration (110-4 mM) of thiamine pyrophosphate (TPP), but eighty percent of normal activity when the assay contained a high (0.4 mM) concentration of TPP. Which one of the following statements concerning this patient is most correct?A. Elevated levels of lactate and pyruvate in the blood reliable predict the presence of PDH deficiency.B. The pati