美国的生化考题

BCH 4013/6013 Exam 1 (01/31/2012)There are 50 questions worth 0.4 points each (total 20 points)1. Which of the following is NOT a basic element of life?A) PhosporusB) HydrogenC) NitrogenD) OxygenE) All of the above are basic elements of life2. Which of the following classes of compounds make up most of the mass of an organism?A) Amino acidsB) ProteinsC) LipidsD) CarbohydratesE) Water3. A hydrogen bond is best defined as:A) A strong chemical bond between hydrogen and carbonB) A weak chemical bond between hydrogen and carbonC) A bond between two hydrogensD) A weak electrostatic bond between hydrogen and oxygen or nitrogen4. The most important buffer in blood is __________.A) Bicarbonate/carbonic acid bufferB) Protein bufferC) Phosphate bufferD) Lactate buffer5. Consider the following molecule. Which arrow is pointing to a peptide bond?A) AB) BC) CD) D6. Which of the following classes of enzymes catalyze reactions involving the cleavage of bondsby the addition of water?A) TransferaseB) HydrolaseC) LyaseD) Ligase N C C N C C H H H H O H H H O DC7. Consider the following reaction data.Alanylanine + water alanine[alanylanine] [water] Rate0.1 0.1 1x 10-40.2 0.1 2x10-40.1 0.2 2x10-40.2 0.2 4x10-4The reaction is ________ order overall.A ZeroB) FirstC) SecondD) ThirdE) Fourth8. An enzyme without its cofactor is called ________A)CoenzymeB)ApoenzymeC)HoloenzymeD)Isoenzyme9. Which of the following is a function of proteins?A) StructureB) MovementC) TransportD) CatalysisE) All of the above are correct10. The term protein refers to amino acid polymers with greater than ________amino acids.A) 10B) 20C) 50D) 10011. Select the coenzyme that DOES NOT participate in electron transfer reactions.A)NADPB)NADC)ATPD)FAD12. The class of enzyme that catalyzes the following reaction is:A) isomeraseB) ligaseC) hydrolaseD) transferase13. What is the maximum number of hydrogen bonds that one water molecule can have with neighboring water molecules?A) 1B) 2C) 3D) 414. Which of the following amino acids is involved in disulfide bonds?A) cysteineB) methionineC) prolineD) none of above15. An apoenzyme combines with a coenzyme to form aA) holoenzymeB) cofactorC) proenzymeD) prosthetic group16. The alteration of enzyme structure on binding of a substrate to an active site is referred to asA) Enzyme denaturationB) Enzyme inhibitionC) Induced fitD) Enzyme activation17. Which of the following properties is NOT characteristic of enzymes?A) Hold the substrate in close proximityB) Alter the equilibrium constant of the reactionC) Reduce the activation energyD) Often use acid-base catalysis18. Primary protein structure refers toA) overall shape of a proteinB) repeated pattern of foldingC) a protein with multiple subunitsD) linear amino acid sequence19. Which of the following statements about a plot of the initial velocity (V0) vs. the concentration of substrate ([S]) for an enzyme that follows Michaelis-Menten kinetics is FALSE?A)As [S] increases, the initial velocity of reaction V0 also increases.B)At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at K mC)The shape of the curve is a hyperbolicD) The y-axis is a rate20. Which amino acid is classified as basic?A) prolineB) cysteineC) glutamineD) lysine21. The K m of an enzymatic reaction is equal toA) the concentration of substrate at equilibriumB) the concentration of product at equilibriumC) the concentration of substrate at one-half maximum velocity (V max)D) the concentration of enzyme at one-half maximum velocity (V max)22. In competitive inhibition, an inhibitor:A)binds at several different sites on an enzyme.B)binds covalently to the enzyme.C)binds only to the ES complex.D)binds reversibly at the active site.23. For an enzyme obeying Michaelis-Menten kinetics, what is the V max if V0 = 35 µmole/min when [S] = K m?A) 35 µmole/minB) 70 µmole/minC) 105 µmole/minD) 140 µmole/min24. Secondary protein structure of refers toA) overall shape of a proteinB) repeated pattern of foldingC) a protein with multiple subunitsD) linear amino acid sequence25. The cleft in the surface of an enzyme where a substrate binds is known as:A) modulator siteB) allosteric siteC) active siteD) oligomeric site26. Hydrogen bonds can occur when hydrogen is covalently bonded to atoms like nitrogen and oxygen. What property of nitrogen and oxygen is important for this?A) atomic massB) ionizabilityC) hydrophobicityD) electronegativity27. Succinic acid dehydrogenase is active only in combination with a nonprotein organic molecule called flavin adenine dinucleotide (FAD). FAD is called aA) proenzymeB) isozymeC) apoenzymeD) coenzyme28. The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics:V0 ( mol/min)Substrate added (mM)217 325 433 488 645 650 0.8 246100 1,000The K m for this enzyme is approximately:A)1 mM.B)2 mM.C)4 mM.D)6 mM.29. To what level of structure do α-helices and β-sheets belong?A)Primary structureB)Secondary structureC)Tertiary structureD)Quaternary structure30. According to Henderson-Hasselbalch equation, when theconcentrations of proton acceptor and proton donor are the same, thenA) the carboxylic acid is totally neutralizedB) only salt forms are presentC) pH = pK aD) pK a = log[proton acceptor]/[proton donor]31. The bonds linking amino acids to form proteins are calledA) glycosidic bondsB) hydrogen bondsC) amino bondsD) peptide bonds32. A denaturing agents disrupt the three-dimensional structures of macromolecules byA) breaking glycosidic bondsB) breaking hydrogen bondsC) breaking peptide bondsD) breaking amide bonds33. Allosteric effectors:A) can be very different in structure than the substrates of the enzymeB) typically bind to sites distant from the active site of an enzyme.C) induce a conformational change in the protein to alter its activity.D) All of the above.34. Buffer systems are effective when the pH values are within ___ pH unit(s) of the pK a value.A) 1B) 3C) 4D) 535. The titration curve of the amino acid glycine reveals a pK1 of 2.34, a pI (isoelectric point) of5.97, and a pK2 of 9.60. When dissolved in water, which ionic species is most likely topredominate at pH = 5.97?A) B) C) D)36. Hydrogen bonds between amino acids in a polypeptide occur between which chemical groups?A) the C=O and C-H groupsB) the C=O and C-R groupsC) the C=O groupsD) the C=O and N-H groups37. The pH inside cells is normally near pH 7. At pH 7 which statement is true about the charges (ionization state) of the alfa-carboxyl and alfa-amino groups of an amino aicd?A) The alfa-carboxyl group is 1- and the alfa-amino group is 1+B) The alfa-carboxyl group is 1+ and the alfa-amino group is 1-C) The alfa-carboxyl group is 1- and the alfa-amino group is unchargedD) Both groups are uncharged (not ionized) at pH 738. What is the primary force that stabilizes repeating secondary structures as found in α-helices and β-turns?A) covalent bondsB) ionic interactionsC) hydrogen bondsD) hydrophobic interactions39. The effect of an enzyme is to:A) lower the activation energyB) shift the equilibrium position of the reaction towards productsC) decrease the free energy of the reaction40. What is the isoelectric point, pI, of glycine? Given pKa1=2.3, pKa2=9.6.A) 9.60B) 5.95C) 11.90D) 2.3041. Most enzymes are:A) ProteinsB) LipidsC) DNAD) Carbohydrates42. The chirality of an amino acid results from the fact that its α carbon:A)has no net chargeB)is a carboxylic acidC)is bonded to four different chemical groupsD)is symmetric43.Hemoglobin is made up of four polypeptide chains (subunits). The maximum degree of protein structure shown by hemoglobin is:A)QuaternaryB)TertiaryC)SecondaryD)Primary44. Based on the Henderson-Hasselbalch equation (shown below), calculate the pH when the ratio of acetic acid to acetate is 10 to 1 (the p K a of acetic acid is 4.76).A) 1.00B) 3.76C) 4.76D) 5.7645.The pH of a sample of blood is 7.4, while gastric juice is pH 1.4. The blood sample has:A)0.6 times the [H+] as the gastric juiceB)6 times lower [H+] than the gastric juiceC)6,000 times lower [H+] than the gastric juiceD)a million (106) times lower [H+] than the gastric juice46. In a highly basic solution, pH = 12, the dominant form of glycine is:A)NH2—CH2—COOHB)NH2—CH2—COO-C)NH3+—CH2—COOHD)NH3+—CH2—COO-47. The three-dimensional structure (native conformation) of proteins is determined primarily byA) noncovalent interactions.B) the other proteins with which it forms a complex.C) its amino acid sequence.D) molecular chaparones.48. Which of the following forces contributes MOST to the primary structure of a protein?A) covalent bondsB) ionic interactionsC) hydrogen bondsD) hydrophobic interactionsE) van der Waals interactions49. Which of the following describes the overall three-dimensional folding of a polypeptide chain?A) Primary structureB) Secondary structureC) Tertiary structureD) Quaternary structure50. Which of the following amino acids has a net positive charge at pH 7?A) leucineB) lysineC) phenylalanineD) glutamic acidAnswer Key to Exam 11. E2. E3. D4. A5. B6. B7. C8. B9. E10. C11. C12. D13. D14. A15. A16. C17. B18. D19. B20. D21. C22. D23. B24. B25. C26. D27. D28. B29. B30. C31. D32. B33. D34. A35. D36. D37. A38. C39. A40. B41. A42. C43. A44. B45. D46. B47. C48. A49. C50. B。