51. Which of the following enzymes is regulated by allosteric regulation in the urea cycle?
(A) Carbamoyl phosphate synthetase I
(B) Glutamine synthetase
(C) Glutamate dehydrogenase
(D) Aspartate aminotransferase

47. Which of the following is   NOT   a ketone body? (A) Acetyl-CoA (B) Acetone (C) β-hydroxybutyrate (D) Acetoacetate

48. Which description is   NOT   correct about the catabolism of amino acids? (A) An early step in the catabolism of amino acids is the separation of the amino group from the carbon skeleton. (B) The amino group is transferred to α-ketoglutarate to form glutamate. (C) The amino group transamination reaction requires the coenzyme pyridoxal phosphate. (D) Glutamate dehydrogenase liberates the amino group as ammonium ion (NH4+) in the liver peroxisome.

49. Which of the following hormones is derived from cholesterol? (A) Progesterone (B) Androgens (C) Estrogens (D) All of the above

50. Which description is   NOT   correct about the nitrogen excretion? (A) Ammonia is highly toxic to animal tissues. (B) In the urea cycle, ornithine combines with ammonia and regenerate in each turn of the cycle. (C) The urea cycle results in a net conversion of fumarate to oxaloacetate. (D) Both of fumarate and oxaloacetate are intermediates in the TCA cycle.

52. Which of the following is an alternative electron donor to the mitochondrial electron transport chain? (A) H2O (B) Succinate (C) Fumarate (D) All of the above

53. Which of the following metabolic reactions mainly occur in the mitochondrial matrix? (A) Gluconeogenesis (B) Pentose phosphate pathway (C) Citric acid cycle (D) Glycolysis

54. Which of the following intermediates is key connection of carbohydrate, protein, and lipid metabolic pathways? (A) Triglyceride (B) Pyruvate (C) Acetyl-CoA (D) Adenosine triphosphate

55. What is the first enzyme in glycolysis? (A) Phosphoglycerate Kinase (B) Enolase (C) Pyruvate Kinase (D) Hexokinase

56. Which of the following enzymes is related to the CO2-assimilating reactions (Calvin cycle) in plants? (A) Aldolase (B) Transketolase (C) Rubisco (D) Hexokinase

57. Many bacteria have thick, rigid extracellular walls that protect them from osmotic lysis. Which of the following is   NOT   found in the cell wall of gram-positive bacteria? (A) Pentaglycine (B) N-Acetylglucosamine (C) N-Acetylmuramic acid (D) Cellulose