20. Which of the following glycolytic intermediates is directly involved in the generation of ATP through substrate-level phosphorylation?
(A) Glucose-6-phosphate.
(B) Phosphoenolpyruvate.
(C) Fructose-1,6-bisphosphate.
(D) Glyceraldehyde-3-phosphate.
(E) 3-phosphoglycerate.

16. During intense physical activity, NADH generated in glycolysis is rapidly reoxidized by which reaction? (A) Reduction of pyruvate to lactate by lactate dehydrogenase. (B) Conversion of glucose-6-phosphate to fructose-6-phosphate. (C) Oxidation of dihydroxyacetone phosphate to glycerol-3-phosphate. (D) Reduction of oxaloacetate to malate. (E) Formation of citrate from oxaloacetate and acetyl-CoA.

17. Arsenic poisoning inhibits which enzyme of the citric acid cycle, thereby impairing oxidative metabolism? (A) Citrate synthase. (B) Malate dehydrogenase. (C) α-Ketoglutarate dehydrogenase. (D) Fumarase. (E) Aconitase.

18. Which glycolytic product serves as the primary precursor for entry into the citric acid cycle? (A) 2-Phosphoglycerate. (B) Glyceraldehyde-3-phosphate. (C) Pyruvate. (D) Glucose-6-phosphate. (E) Fructose-1,6-bisphosphate.

19. Which polysaccharide is found in the plant cell wall and provides structural support? (A) Glycogen (B) Amylopectin (C) Cellulose (D) Starch (E) Chitin

21. What is the major driving force for the formation of tertiary structures in cytoplasmic proteins? (A) Formation of peptide bonds. (B) Hydrogen bonding between backbone atoms. (C) Hydrophobic interactions among nonpolar side chains. (D) Covalent bonding between side chains of amino acids. (E) Ionic interactions between side chains of amino acids.

22. What is the most obvious structural feature that differentiates parallel β-sheets from antiparallel β-sheets? (A) The total number of the hydrogen bonds. (B) The direction of the peptide chains relative to each other. (C) The amino acid composition of the strands. (D) The presence of disulfide bonds. (E) The length of strands in the sheet.

23. In a cytoplasmic and globular protein, where would you most likely find hydrophobic amino acids? (A) On the surface of the protein. (B) In the interior of the protein. (C) Randomly distributed throughout the protein. (D) In the α-helices of a protein. (E) Around metal ions, such as .

24. What effect does a competitive inhibitor have on enzyme kinetics? (A) Decreases and does not change (B) Increases and does not change (C) Decreases both and (D) Does not affect either or . (E) Increases and decreases

25. In Michaelis-Menten kinetics, what assumption is made about the enzyme-substrate complex during the steady-state phase of the reaction? (A) The concentration of the enzyme-substrate complex is constant. (B) The enzyme is saturated with substrate. (C) Product concentration remains constant. (D) The product is formed as soon as the substrate binds to the enzyme. (E) The enzyme binds to substrate irreversibly.

26. Which following statement is correct in human cells? (A) Catabolism is usually an endergonic reaction in human cells. (B) Most metabolisms follow the thermodynamic laws, but few do not follow the first law of thermodynamics because human beings need to eat every day. (C) Anabolism often comes along with ATP generation in human cells. (D) The Complex III in the oxidative phosphorylation is not a proton pump. (E) Cytochrome C is a proton carrier that delivers the proton to Complex IV in oxidative phosphorylation.