21. Which of the following does not specifically cause a membrane to be more rigid or fluid, but rather causes the Tm to occur over a greater range?
(A) increasing the content of unsaturated fatty acids
(B) raising the temperature
(C) increasing the cholesterol content
(D) decreasing the phosphatidylcholine content while increasing the phosphatidylethanolamine content
(E) all of the above

17. Which of the following is the regulatory step in cholesterol synthesis? (A) HMG-CoA synthase (B) HMG-CoA lyase (C) HMG-CoA reductase (D) squalene synthase (E) squalene epoxidase

18. In the citric acid cycle, acetyl-CoA reacts with ________ to produce _________. (A) fumarate； ᵦ-ketoglutarate (B) oxaloacetate； citrate (C) citrate； isocitrate (D) succinyl-CoA； oxaloacetate (E) malate； cis-aconitate

19. Which of the following correctly identifies key elements present on the exterior of Gram-negative (GN) and Gram-positive (GP) bacteria? (A) GN: single lipid bilayer； GP: two lipid bilayers (B) GN: single peptidoglycan layer； GP: multiple peptidoglycan layers (C) GN: extensively crosslinked peptidoglycans； GP: uncrosslinked peptidoglycan (D) GN: contains both N-acetylmuramic acid and N-acetylglucosamine； GP: contains only N-acetylmuramic acid (E) none of the above

20. How many stereoisomers would be expected from a ketohexose? (A) 4 (B) 8 (C) 16 (D) 32 (E) 64

22. Movement of ions across a cell membrane by the Na/K ATPase is best described as ________. (A) sodium moved outside to inside, potassium inside to outside (B) sodium moved inside to outside, potassium outside to inside (C) sodium moved inside to outside, potassium inside to outside (D) sodium moved outside to inside, potassium outside to inside (E) none of the above

23. Which of the following formulas would be a carbohydrate (A) C5H12O5 (B) C4H8O6 (C) C6H10O6 (D) C3H8O3 (E) C6H12O6

24. Which enzyme catalyzes the primary regulation site of glycolysis? (A) hexokinase (B) phosphofructokinase-1 (C) glyceraldehyde-3-phosphate dehydrogenase (D) phosphoglycerate kinase (E) pyruvate kinase

25. Which of the following shows the overall equation for the light reactions? (A) 2 H2O + 1 NADP+ → 1 H+ + O2 + 1 NADPH, requires 4 photons (B) 2 H2O + 1 NADP+ → 1 H+ + O2 + 1 NADPH, requires 8 photons (C) 2 H2O + 2 NADP+ → 2 H+ + O2 + 2 NADPH, requires 4 photons (D) 2 H2O + 2 NADP+ → 2 H+ + O2 + 2 NADPH, requires 8 photons (E) 2 H2O + 2 NADP+ → 2 H+ + O2 + 2 NADPH, requires 16 photons

26. Which of the following would likely form micelles in an aqueous solution? (A) hexane (B) glucose (C) glutamic acid (D) dodecanoic acid (E) none of the above

27. Which of the following techniques was used to determine the double helical structure of DNA? (A) NMR spectroscopy (B) X-ray diffraction (C) Raman spectroscopy (D) UV/Vis spectroscopy (E) IR spectroscopy