7. Which enzyme catalyzes the rate-limiting step in the citric acid cycle and is inhibited by ATP?
(A) Citrate synthase.
(B) a-ketoglutarate dehydrogenase complex.
(C) Isocitrate dehydrogenase.
(D) Malate dehydrogenase.
(E) Succinate dehydrogenase.

3. In patients with certain genetic diseases, a defect in the carnitine transporter can lead to which of the following conditions? (A) Fatty acids cannot enter the mitochondria for oxidation. (B) Glucose cannot enter the mitochondria for oxidation. (C) Proteins cannot enter the mitochondria. (D) ATP synthesis increases. (E) Elevation of intracellular ketone body levels.

4. Which of the following statements regarding the functions of RNA and DNA is INCORRECT? (A) DNA is primarily responsible for storing genetic information. (B) mRNA carries genetic information and is used for protein synthesis. (C) tRNA is involved in the process of protein translation. (D) rRNA is a major component of ribosomes and participates in protein synthesis. (E) miRNA can regulate gene expression but cannot degrade mRNA.

5. Under anaerobic conditions, ATP generation primarily relies on which of the following pathways? (A) Electron transport chain (B) Oxidative phosphorylation (C) Glycolysis (D) Citric acid cycle (E) β-oxidation

6. Which of the following enzymes is directly responsible for the elongation of fatty acid chains during de novo fatty acid synthesis? (A) Acetyl-CoA carboxylase. (B) Acyl-CoA dehydrogenase. (C) Fatty acid synthase. (D) B-ketoacyl-ACP synthase. (E) Carnitine acyltransferase.

8. Regarding eukaryotic translation and the structure and function of tRNA, which of the following statements is correct? (A) During translation, the small ribosomal subunit is responsible for peptide bond formation, while the large subunit scans and pairs the ribosome with the start codon of the mRNA. (B) During the recognition and attachment of the correct amino acid to tRNA, aminoacyl-tRNA synthetase verifies the side-chain structure of the amino acid and the anticodon of the tRNA to ensure specificity. (C) The E-site of the ribosome is the entry site for aminoacyl-tRNA, while the P-site is the location where decoding occurs. (D) Eukaryotic translation initiation requires eIF2 (eukaryotic initiation factor 2) to assist in loading the initiator tRNA into the large ribosomal subunit and directly position the start codon on the mRNA via the 5' cap structure. (E) The TYC arm of tRNA interacts with the ribosome to help tRNA enter the ribosome, while the DHU arm is responsible for the specific recognition by aminoacyl-tRNA synthetase.

9. Which of the following substances is NOT a precursor or intermediate in cholesterol synthesis? (A) Acetyl-CoA. (B) Acetoacetyl-CoA. (C) Mevalonic acid. (D) Squalene. (E) Phosphatidic acid.

10. Which of the following substances is the starting material for de novo purine nucleotide synthesis? (A) Aspartate. (B) Glycine. (C) Glutamine. (D) All of the above. (E) None of the above.

11. Which of the following mechanisms is primarily involved in repairing double-stranded breaks in DNA? (A) Non-homologous end joining (NHEJ). (B) Homologous recombination. (C) Base excision repair (BER). (D) Nucleotide excision repair (NER). (E) Both A and B.

12. Which of the following substances can activate phosphofructokinase-1 (PFK-1) and stimulate glycolysis? (A) ATP. (B) Citrate. (C) AMP. (D) Fatty acid. (E) Acetyl-CoA.

13. Which of the following statements about cyclin-dependent kinases is INCORRECT? (A) Different types of cells regulate the cell cycle through distinct CDK complexes with specific cyclins. (B) CDK activity fluctuates depending on the stage of the cell cycle. (C) CDK activity is controlled by mechanisms such as gene expression, phosphorylation, and protein degradation. (D) Cyclins are essential regulators of CDK activity. (E) CDKs regulate proteins that drive cell cycle progression.