55. The Hsp70 molecular chaperones are a group of proteins that assist nascent protein folding. Which of the following statements about the E. coli Hsp70 is NOT correct?
(A) In Hsp70-assisted folding, the chaperone binds to nascent polypeptide chains while they are still on the ribosomes.
(B) The DnaJ protein binds unfolded proteins during protein synthesis and delivers them to the DnaK: ATP complex.
(C) The Dnak protein recognizes exposed, extended regions of polypeptides that are rich in hydrophilic residues.
(D) Interaction of DnaK with DnaJ triggers the ATPase activity of DnaK. The resulting DnaK: ADP complex forms a stable complex with the unfolded polypeptide.
(E) The reaction cycle requires a nucleotide exchange protein GrpE.

51. Based on the enzyme reaction plot shown below, which of the following statements is correct? (A) The of hexokinase IV for glucose is ~10 mM. (B) Hexokinase I works more efficiently than hexokinase IV when the blood glucose concentration is higher than 10 mM. (C) The of hexokinase I for glucose is ~5 mM. (D) Hexokinases catalyze a reaction that adds an AMP group to glucose. (E) At normal fasting conditions, hexokinase IV works better than hexokinase I .

52. Which of the following statements about the initial step of the reaction catalyzed by thermolysin is NOT correct? (A) The enzyme reaction involves the general acid-base catalysis. (B) A glutamate residue deprotonates water and promotes hydroxide attack on the carbonyl carbon of the substrate. (C) The ion stabilizes the buildup of negative charge on the peptide carbonyl oxygen. (D) Collapse of the unstable tetrahedral intermediate links the substrate to the glutamate residue covalently. (E) The enzyme is a member of hydrolases.

53. Which of the following is NOT a property of phosphoglucoisomerase? (A) The carbonyl oxygen of glucose-6-phosphate is shifted from position C-1 to C-2. (B) The enzyme catalyzes the conversion of glucose-6-phosphate to glucose-1- phosphate. (C) The reaction involves the opening of the pyranose ring. (D) The reaction involves an aldose and a ketose. (E) The reaction involves the formation of an enediol intermediate.

54. Proteins can be modified with small regulatory proteins like ubiquitins and small ubiquitin-like protein modifiers (SUMO). Which of the following descriptions about SUMO is NOT correct? (A) SUMO are a highly conserved family of proteins found in all eucaryotes. (B) SUMO are covalently ligated to lysine residues in target proteins. (C) Sumoylated proteins are primarily targeted to the proteasome for destruction. (D) Protein sumoylation is primarily a 3-enzyme conjugating system. (E) Protein sumoylation can be reversed by a small number of isopeptidases that cleave the target protein-SUMO linkages.

56. Which of the following descriptions about pyrimidine synthesis is NOT correct? (A) The pathway commences with the conversion of bicarbonate and glutamine into carbamoyl phosphate. In mammalian cells, carbamoyl phosphate synthetases- II is the major enzyme responsible for the reaction. (B) Carbamoyl phosphate reacts with aspartate to produce carbamoyl aspartate. The enzyme aspartate transcarbamoylase catalyzes this reaction. (C) The enzyme dihydroorotase converts carbamoyl aspartate into dihydroorotate. This step does not involve the incorporation of any atoms from the other substrates. (D) Dihydroorotate is combined with 5-phosphoribosyl-1-pyrophosphate to form UMP. This step is catalyzed by orotate phosphoribosyltransferase. (E) Unlike purines, pyrimidines are not synthesized as nucleotide derivatives. The synthesis of the pyrimidine ring is completed before a ribose-5-phosphate moiety is attached.

57. Which of the following statements about E. coli RNA polymerase is correct? (A) The enzyme is composed of four subunits, namely αβρσ. (B) It requires the assistance of a DNA helicase to unwind double-stranded DNA for initiation of transcription. (C) The o subunit is responsible for recognizing the promoter sequence. (D) The o subunit is dissociated from the enzyme complex when the mRNA synthesis is complete. (E) The growth direction of the RNA chain is from 3' to 5'.

58. Which of the following statements about eukaryotic RNA polymerase II is correct? (A) The yeast RNA polymerase II is composed of 12 different protein subunits. (B) All three eukaryotic RNA polymerases share two common protein subunits. (C) The enzyme is usually located in the nucleolus. (D) The enzyme is mainly responsible for the transcription of tRNA and 5S rRNA genes. (E) Among the three eukaryotic RNA polymerases, RNA polymerase II activity is less inhibited by a-amanitin.

59. Which of the following statements about kcat is correct? (A) kcat is an indicator of the purity of an enzyme preparation. (B) kcat represents the substrate concentration required for an enzyme to reach50% of its maximum reaction velocity. (C) kcat reflects the half-life of an enzyme. (D) kcat represents the pH value at which the product dissociated from the enzyme. (E) kcat is defined as the number of substrates converted to products per enzyme molecule per unit time when the substrate concentration is saturated.

60. The structural and functional advantages of protein quaternary association do NOT include: (A) It can improve protein stability by reducing the combined molecular surface- to-volume ratio. (B) It can significantly enhance the efficiency of protein transportation. (C) The combination of different subunits can achieve synergy and function regulation. (D) Because same protein subunits can be assembled to form enzymes of different activities, genes can be used more efficiently. (E) Several functional groups required for the catalytic reaction can be brought together to form a functional enzyme catalytic center NTHU114

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