31. Which of the following equations represents the Michaelis-Menten equation?
(A)
(B)
(C)
(D)
(E) ν = E-[ES]

27. Which statement about the transition state of an enzyme-catalyzed reaction is true? (A) The transition state is identical to the enzyme-substrate complex. (B) The transition state always has a lower free energy than the substrate. (C) Enzymes form a lower-energy transition state complex, reducing activation energy. (D) The transition state cannot be bound by an enzyme due to its instability. (E) Enzymes stabilize the substrate more than the transition state.

28. The tautomeric forms of bases can lead to: (A) Base-pair mismatches and spontaneous mutations. (B) Higher melting temperature (Tm). (C) Increased stability of the DNA helix. (D) Covalent bonds between bases across strands. (E) Accelerated replication speed in eukaryotes.

29. When a ligand binds a receptor tyrosine kinase, the first step in the signaling cascade is usually: (A) Conversion of GTP to cGMP. (B) GTP hydrolysis by the α-subunit of the G protein. (C) CAMP formation by adenylyl cyclase. (D) Internalization of the receptor into lysosomes. (E) Auto-phosphorylation of specific tyrosine residues on the receptor.

30. What role does phospholipase C play in signal transduction? (A) Activates adenylate cyclase. (B) Produces IP3 and DAG from phosphatidylinositol 4,5-bisphosphate (PIP2). (C) Converts cAMP to AMP. (D) Activates protein kinase C directly. (E) Converts GTP to GDP.

32. What is the effect of a competitive inhibitor on an enzyme-catalyzed reaction? (A) Has no effect on either (B) Increases without affecting . (C) Increases without affecting (D) Decreases without affecting (E) Decreases

33. Which of the following statements is   incorrect   regarding the cholesterol metabolism? (A) Chylomicrons contain a high portion of cholesterol, which are synthesized from dietary fats in the endoplasmic reticulum of enterocytes. (B) Cholesteryl esters are formed in the liver, converting the cholesterol to a more hydrophobic form that can be carried in lipoproteins to tissues that need cholesterol. (C) Bile acids, one of the forms of cholesterol exported from the liver, are the principal components of bile, a fluid stored in the gallbladder and excreted into the small intestine. (D) The uptake of cholesterol from the bloodstream is regulated by receptor-mediated endocytosis. (E) Excess cholesterol in extrahepatic tissues, including macrophages and foam cells, is transported back to the liver in reverse cholesterol transport.

34. Ketone bodies can be the fuel source to support the whole-body metabolism. Which of the following statements regarding ketone bodies is correct? (A) Acetoacetate, β-ketobutyrate, and acetone are the three main types of ketone bodies produced in the liver. (B) Ketone body production leads to a decrease in blood pH, which can result in ketoacidosis if the production exceeds the body's ability to utilize them. (C) Ketone bodies are produced during the citric acid cycle, but only when there is an excess of glucose in the body. (D) In the fasting state, the body increases ketone body production to spare glucose for the brain because ketone bodies cannot cross the blood-brain barrier. (E) Ketone bodies are synthesized from glucose in patients with diabetes because of the insufficient of insulin level.

35. Which of the following is   not   required in the biosynthesis of fatty acids? (A) Acetyl-CoA (B) Biotin (C) (D) Malonyl-CoA (E) NADH

複選題36. The enzymes of fatty acid oxidation are located in the mitochondria matrix, so free fatty acids must be transported through the shuttle into the mitochondria. Which of the following statements regarding the shuttle is correct? (A) Free fatty acid must be activated by a fatty acyl-CoA synthetase, through the hydrolysis of one high-energy bond in ATP, to yield a fatty acyl-CoA before entering the shuttle. (B) The enzyme responsible for esterifying carnitine with acyl-CoA in both inner and outer mitochondria membranes is the rate-limiting step for oxidation. (C) Coenzyme A in the cytosol is largely used in the oxidative degradation of fatty acids. (D) This shuttle plays a crucial role in transporting medium-chain fatty acids into the mitochondria for beta-oxidation. (E) Fatty acyl-CoA destined for mitochondria oxidation must be attached to carnitine to be shuttled across the inner mitochondria membrane.

37. The unsaturated fatty acid contains one or more double bonds. Which of the following statements regarding the metabolism of unsaturated fatty acid is correct? (A) The double bonds of unsaturated fatty acids are in the cis configuration, making them to easily react with hydratase for oxidation. (B) When oxidizing an unsaturated fatty acid, the double bond must be first reduced to a single bond before it can be further processed in the beta-oxidation pathway. (C) The unsaturated fatty acid, compared to saturated fatty acid with the same carbon numbers, causes a change of acetyl-CoA production in the oxidation pathway. (D) The oxidation of a monounsaturated fatty acid may skip one reaction of dehydrogenation during beta-oxidation due to the presence of the cis double bond in the fatty acid chain. (E) The oxidation of unsaturated fatty acids requires the cofactor biotin to catalyze the reaction.