39. Correct statements regarding arachidonic acid include all of the following except_______ .
(A) it is a precursor of thromboxane A₂
(B) it activates lipoxygenase
(C) it is a 20-carbon fatty acid with three double bonds
(D) it can be derived from linoleic acid
(E) it is esterified to the sn-2 position of glycerophospholipids

35. Which one of the following statements relating to lipids and membranes is correct? (A) Triacylglycerols are the major component of most cell membranes. (B) Clusters of cholesterol molecules are generally used to provide ion channels. (C) Na+ and K+ ions readily diffuse through the lipid bilayer. (D) Both saturated and unsaturated fatty acyl groups are used in typical phospholipids. (E) All phospholipids incorporate a glycerol unit as part of their structure.

36. Which one of the following statements about cholesterol is correct? (A) The complete oxidation of cholesterol to CO2 and H2O occurs in the liver as an energy source. (B) Cholesterol esters are an important component of the outer monolayer of lipoproteins. (C) Some cholesterol synthesis occurs in the liver but most takes place in other tissues. (D) Beta-hydroxy-beta-methylglutaryl-CoA is generated from three molecules of acetyl-CoA and is an intermediate in cholesterol biosynthesis. (E) Cholesterol is an important precursor for the production of the various prostaglandins, important in a broad range of physiological roles. 

37. Which of the following enzymes in liver is/are activated as a result of an elevated insulin level after a meal? (A) cAMP-dependent protein kinase and adenylate cyclase (B) Fructose 1,6 bisphosphate (FBPase-1) (C) Glycogen phosphorylase, phosphokinase (D) Glycogen synthase, phosphofructo-kinase-1 (PFK-1), and pyruvate kinase (E) Phosphoenolpyruvate carboxykinase (PEPCK)

38. Oncogenes that have tyrosine kinase activity_______ . (A) probably correspond to protooncogenes that are growth factor receptors (B) probably correspond to protooncogenes that are polypeptide growth factors (C) are probably Gs proteins (D) are probably Gi proteins (E) are probably DNA binding proteins

40. The cost in high-energy phosphate bonds for the formation of 1 mol of glucose from lactate is_______ . (A) 8 mol of ATP (B) 6 mol of ATP (C) 4 mol of ATP (D) 2 mol of ATP (E) none of the above

41. In the sequence of reactions that convert lactate to glucose in cells capable of gluconeogenesis, three reactions are used to bypass enzymes of the glycolytic pathway in which glucose is converted to lactate. All of the following enzymes fall into this category except_______ . (A) pyruvate carboxylase (B) pyruvate dehydrogenase (C) phosohoenolpyruvate carboxykinase (D) fructose 1,6-diphosphatase (E) glucose 6-phosphatase

42. Carbon monoxide inhibits mitochondria electron transport by_______ . (A) binding to hemoglobin in the erythrocytes and so blocking the transport of oxygen to tissues (B) binding to the oxygen-binding site of cytochrome oxidase (C) blocking electron transport at the level of the cytochrome b-cytochrome c1 complex (complex III) (D) combining with coenzyme Q and preventing its interaction with nonheme iron-surfur-protein center of complex II (E) inhibiting the electron transfer of complex I

43. If the substrate concentration in an enzyme catalyzed reaction is equal to 0.5 Km, the initial reaction velocity will be _______. (A) 0.25 Vmax (B) 0.33 Vmax (C) 0.50 Vmax (D) 0.67 Vmax (E) 0.75 Vmax

44. An enzyme that catalyzes the conversion of an aldose sugar to a ketose sugar would be classified as one of the_______. (A) oxidoreductases (B) transferases (C) hydrolases (D) isomerases (E) lyases

45. An analysis of chromosomal DNA, using the Southern blot technique, involves the following five major steps: ①Autoradiography； ②Blotting； ③ Cleavage；④Electrophoresis； ⑤Hybridization；Which of the following sequences of steps best illustrates this technique? (A)①②③④⑤ (B) ①③②④⑤ (C) ③⑤②④①(D) ③②⑤④①(E) ③④②⑤①