64. 5-phosphoribosyl-1-pyrophosphate (PRPP) is a precursor in the synthesis of all of the following products except ________.
(A) histidine
(B) tryptophan
(C) arginine
(D) UMP
(E) AMP

60. Radiolabelled isotope dating is an important method to determine the age of a fossil. A 14C content analysis of an animal fossil showed that its content is 0.01562 fold as much 14C as the atmosphere. The half-life of 14C is 5730 years. The age of the fossil is close to which of the following? (A) 1000 years (B) 5730 years (C) 35000 years (D) 70000 years (E) 100000 years

61. Which of the following descriptions about the Michaelis-Menten equation is false? (A) KM measures the substrate concentration at which the reaction rate is 1/2Vmax. (B) An enzyme with a low KM means that it has low affinity for its substrate. (C) An enzyme with a low kcat means that it has a low catalytic rate. (D) The turnover number, kcat, measures the rate of the catalytic process. (E) The ratio kcat/KM is a convenient measure of enzyme efficiency.

62. Which description about Hb (hemoglobin) is false? (A) HbF has an α2γ2 structure. (B) HbA has an α2β2 structure. (C) HbF has a much higher affinity for 2,3-BPG than HbA does. (D) 2,3-BPG lowers the O2 affinity of HbA. (E) 2,3-BPG is found inside red blood cells.

63. The carbon skeleton produced by transamination of aspartate enters the citric acid cycle as ______. (A) acetyl-CoA (B) pyruvate (C) fumurate (D) oxaloacetate (E) α-ketoglutarate

65. In eukaryotic cells, mRNA modification includes __________. (A) splicing out exons and join introns (B) add a cap at 3’ end to protect the 3’ end (C) add a phosphate group at 5’ end to increase stability (D) remove nucleotides at 3’ end before addition of a poly A tail (E) remove 3’UU and attach CCA

66. What is the appropriate order for oxidation of glucose to CO2, H2O and ATP? 1.convert pyruvate to acetyl CoA 2.electron-transport chain 3.citric acid cycle 4.oxidative-phosphorylation 5.glycolysis (A) 3→5→1→4→2 (B) 5→1→3→2→4 (C) 1→4→5→2→3 (D) 3→1→4→2→5 (E) 4→1→3→5→2

67. Cooperative binding of a ligand to a protein is a form of allosteric binding. Which of the following statements is false? (A) It is usually associated with proteins with multiple subunits. (B) The binding of one ligand affects the affinities of other unfilled binding sites. (C) The Hill plot results in a hyperbolic curve. (D) It results in a sigmoidal binding curve. (E) Hill coefficient (nH) is a measure of the degree of cooperativity.

68. Ubiquitin is a small protein which is covalently linked to proteins designated for destruction via ____. (A) ATP-dependent proteases in lysosomes (B) ATP-dependent proteases in proteasomes (C) ATP-dependent proteases in ribosomes (D) ATP-independent proteases in endosomes (E) ATP-independent proteases in peroxisomes

69. What of type reaction promotes the conversion of phosphatidylserine to phosphatidylethanolamine? (A) transamination (B) acetylation (C) dehydrogenation (D) methylation (E) decarboxylation

70. What compound does not exist in the glyoxylate cycle? (A) citrate (B) α-ketoglutarate (C) isocitrate (D) malate (E) oxaloacetate