18. The following molecule is an irreversible inhibitor of which enzyme of nucleotide metabolism?

(A) Thymidine kinase
(B) Thymidylate synthase
(C) Ribonucleotide reductase
(D) dCMP deaminase
(E) CTP synthetase

1. Which of the following monosaccharides is NOT an aldose? (A) Erythrose (B) Fructose (C) Glucose (D) Glyceraldehyde (E) Ribose

2. Which of the following is NOT a characteristic of carbohydrates in cells? (A) They serve as energy stores in both plants and animals. (B) They are major structural components of plant tissues. (C) They act as binding sites for proteins. (D) They are organic catalysts. (E) They play a role in cell-cell recognition.

3. Which of the following statements about the pentose phosphate pathway is correct? (A) It generates 36 moles of ATP per mole of glucose consumed. (B) It generates 6 moles of CO₂ for each mole of glucose consumed (C) It provides precursors for the synthesis of nucleotides. (D) It is present in plants, but not in animals. (E) It is a reductive pathway; it consumes NADH.

4. Which of the following contributes to the structural rigidity of cellulose? (A) Adjacent glucose polymers are stabilized by hydrogen bonding. (B) Glucose residues are joined by a-1,4 linkages. (C) Cellulose is a highly branched molecule. (D) The conformation of the glucose polymer is a coiled structure. (E) Adjacent glucose polymers are covalently linked by short peptides.

5. Why are sugars usually found as phosphorylated derivatives in cells? (A) Phosphorylated sugars are important in regulating cellular pH. (B) Unphosphorylated sugars can be transported across cell membranes. (C) Unphosphorylated sugars are rapidly degraded by cellular enzymes. (D) Phosphorylated sugars encode genetic information. (E) None of the above is a correct explanation.

6. Coconut oil contains only a very small amount of unsaturated fatty acids. How can it still have a low melting point? (A) (B) It contains a lot of long-chain fatty acids. It contains mostly short-chain fatty acids. (C) It has only a few hydrogen bonds per fatty acid chain. (D) A and C are true. (E) B and C are true.

7. Which of the following statements is true of lipids? (A) Many contain fatty acids in ester or amide linkage. (B) Glycerophospholipids are found only in the membranes of plant cells. (C) Testosterone is an important sphingolipid found in myelin. (D) They are more soluble in water than in chloroform. (E) Most are simply polymers ofisoprene.

8. The polar head group of cholesterol is: (A) the alkyl side chain. (B) glycerol. (C) the hydroxyl group. (D) the steroid nucleus. (E) choline.

9. Which of the following statements is true concerning integral membrane proteins? (A) Hydrophobic interactions anchor them within the membrane. (B) Ionic interactions and hydrogen bonds occur between the protein and the fatty acyl chains ofthe membrane lipids. (C) These proteins can be solubilized by a solution of high ionic strength. (D) Hydropathy plots can be used to determine the amino acid sequence of the protein. (E) All of the above.

10. Cyclic AMP (cAMP) is important to cell function for all the following reasons EXCEPT: (A) it provides information about the extracellular environment. (B) it permits a large intracellular response to relatively weak extracellular signals. (C) it provides a site for integrating the metabolic requirements of cells. (D) it reversibly regulates enzymatic activity in cells. (E) it is a source of energy for cells.

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