31. When alanine undergoes transamination with α-ketoglutarate, it will be converted to:
(A) glutamate.
(B) malate.
(C) pyruvate.
(D) oxaloacetate
(E) glycine.

32. Which of the following statements about the reactions involved in amino acid metabolism is       false      ? (A) The activity of glutamine synthetase is regulated both allosterically and by covalent modification. Adenylation of glutamine synthetase stimulates its activity. (B) D-amino acid oxidase is present in humans, and participates in the pathways of glycine degradation. (C) The reaction of the combination of ammonia with glutamate to form glutamine is catalyzed by glutamine synthetase. ATP is required and γ-glutamyl phosphate is an intermediate in the reaction. (D) generated in liver mitochondria is immediately used, together with CO2 (as ), to form carbamoyl phosphate. This ATP-dependent reaction is catalyzed by carbamoyl phosphate synthetase I. (E) Alanine can play the role to transport ammonia from skeletal muscles to the liver. In muscles, glutamate can transfer its α-amino group to pyruvate to form alanine by alanine aminotransferase.

33. Which of the following statements about the reactions involved in the biosynthesis of amino acids is       false      ? (A) Animals can produce tyrosine directly from phenylalanine through hydroxylation. (B) Asparagine is not an essential amino acid in human. It is synthesized by amidation of aspartate, with glutamine donating the . (C) Chorismate is the parent compound for the synthesis of amino acids with aromatic ring. (D) Tyrosine can give rise to a family of neurotransmitter that includes dopamine and norepinephrine. (E) Glutamate can give rise to γ-aminobutyrate (GABA). It is a decarboxylation reaction requiring biotin.

34. Which of the following statements about metabolism in the mammalian liver is       false      ? (A) Most amino acids are metabolized in the liver; however, the three amino acids with branched side chains (leucine, isoleucine, and valine) are oxidized as fuels primarily in muscle, adipose, kidney, and brain. (B) The hepatocytes can convert glucose 6-phosphatase to glucose, and release glucose into the bloodstream. (C) Glycogen is the preferred fuel for energy production in hepatocytes. (D) Most plasma lipoproteins are synthesized in the liver. (E) The enzymatic complement of liver tissue changes in response to changes in the diet.

35. Which one of the following statements is       false      ? (A) At rest, fatty acids are the preferred fuel in skeletal muscle. (B) Elevated epinephrine levels stimulate fatty acid mobilization in the adipose tissue. (C) An elevated insulin level in the blood stimulates synthesis of fatty acids and triacylglycerols in the liver. (D) An elevated glucagon level in the blood stimulates fatty acid mobilization in the adipose tissue. (E) Elevated epinephrine levels inhibit gluconeogenesis in the liver.

36. Which of the following descriptions about the effects of insulin is       correct      ? (A) An elevated insulin level in the blood inhibits glycogen synthesis in the liver and muscle. (B) An elevated insulin level in the blood inhibits glucose uptake by the liver. (C) An elevated insulin level in the blood inhibits glucose uptake by the adipose tissue. (D) An elevated insulin level in the blood stimulates glycogen breakdown in liver. (E) An elevated insulin level in the blood stimulates glycosis in liver.

37. An elevated insulin level in the blood stimulates synthesis of fatty acids in the liver by: (A) activation of phosphofructokinase-2. (B) activation of phosphofructokinase-1. (C) inactivation of glycogen phosphorylase. (D) activation of acetyl-CoA carboxylase. (E) inhibition of triacylglycerol lipase.

38. Fructose 2,6-bisphosphate (F26BP) is a potent regulator of glycolysis and gluconeogenesis. Which of the following descriptions is       correct      ? (A) The cellular concentration of F26BP is determined by the relative rates of its synthesis by fructose 2,6-biphosphatase (FBPase-2) and breakdown by phosphofructokinase-2 (PFK-2). (B) F26BP is an allosteric activator for the enzyme fructose 1,6-biphosphatase (FBPase-1). It activates FBPase-1 and stimulates glycosis in liver. (C) Insulin increases the cellular concentration of F26BP by activating a cAMP-dependent kinase that phosphorylates PFK-2. (D) Phosphorylation of the bifunctional enzyme PFK-2 and FBPase-2 inhibits PFK-2 activity and stimulates FBPase-2 activity, leading to breakdown of F26BP. (E) An elevated level of glucagon or epinephrine increases the cellular concentration of F26BP.

39. One distinction between peptide and steroid hormones is that steroid hormones: (A) bind to their receptors with low affinity, whereas peptide hormones bind with high affinity. (B) bind to nuclear receptors, whereas peptide hormones bind to cell surface receptors. (C) are less stable than peptide hormones. (D) are generally water-soluble, whereas peptide hormones are water-insoluble. (E) act through specific receptors, whereas peptide hormones act through nonspecific receptors.

40. Which one of the following descriptions about the biosynthesis of nucleotides is       correct      ? (A) The ribosyl phosphate moiety needed for the synthesis of orotidylate, inosinate, and guanylate is provided most directly by ribose 5-phosphate. (B) Deoxyribonucleotides are derived from the corresponding ribonucleotides by direct reduction at the 3'-carbon atom of the D-ribose. (C) The immediate precursor of thymidylate (dTMP) is dUMP. The conversion of dUMP to dTMP is a reaction of deamination. (D) The enzyme xanthine oxidase plays a critical role in the salvage pathways for the formation of nucleotides. (E) Formation of deoxyribonucleotides is catalyzed by ribonucleotide reductase, in which its substrates are ribonucleoside diphosphates.

41. Which of the following statements is       correct      ? (A) When a solution of DNA is heated slowly until the tm is reached, the DNA molecules are completely denatured at this temperature. (B) In double-stranded DNA, only a right-handed helix is possib (C) The pentoses found in nucleic acids are always in the β-furanose forms. (D) The nucleic acid bases absorb ultraviolet light maximally at 280 nm. (E) In double-stranded DNA, the sequence of bases has no effect on the overall structure.

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