8. What is the purpose of using reverse transcriptase in DNA-based technologies?
(A) To transcribe RNA into DNA.
(B) To replicate DNA. 
(C) To cut DNA at specific sites.  
(D) To ligate DNA fragments.
(E) To amplify proteins.

4.Which amino acid exhibits a specific UV absorption at 280 nm? (A) Lys (B) Tyr (C) His (D) Gln (E) Cys

5. Given an amino acid titration curve shown in the figure. What is its isoelectric point (pI)?(A) 2.0 (B) 4.0 (C)7.0 (D)10.0 (E) 12.0

6. Both water and glucose possess an-OH group that can react with the terminal phosphate of ATP in a reaction facilitated by hexokinase. Despite this similarity, glucose is approximately a million times more reactive as a substrate compared to water. The most plausible explanation for this difference is:(A)Glucose has more -OH groups per molecule than does water. (B) The-OH group of water is attached to an inhibitory H atom, while the glucose-OH group is attached to C. (C) The larger glucose binds better to the enzyme； it induces a conformational change in hexokinase that brings active-site amino acids into position for catalysis. (D) Water and the second substrate, ATP, compete for the active site resulting in a competitive inhibition of the enzyme. (E)Water normally will not reach the active site because it is hydrophobic.

7. In living cells, nucleotides and their derivatives can serve as: (A) carriers of metabolic energy. (B) enzyme cofactors. (D) precursors for nucleic acid synthesis. (E) All of the above. (C) intracellular signals.

9. CRISPR-Cas9 technology is used for: (A) DNA amplification. (B) gene silencing. (D) protein synthesis. (E) DNA repair.(C) gene editing.

10. Which of the following statements concerning receptor enzymes is correct? (A) They are not usually membrane-associated proteins. (B) They contain an enzyme activity that acts upon a cytosolic substrate. (C) They contain an enzyme activity that acts upon the extracellular ligand. (D) They have a ligand-binding site on the cytosolic side of the membrane. (E) They have an active site on the extracellular side of the membrane.

11. The E. coli recombinant plasmid pBR322 has been widely utilized in genetic engineering experiments. pBR322 has all of the following features except: (A) A number of conveniently located recognition sites for restriction enzymes. (B) A replication origin, which permits it to replicate autonomously. (C) Resistance to antibiotics, which permits rapid screening for recombinant plasmids containing foreign DNA. (D) Small overall size, which facilitates entry of the plasmid into host cells. (E) A number of palindromic sequences near the EcoRI site, which permit the plasmid to assume a conformation that protects newly inserted DNA from nuclease degradation.

12. Which is a characteristic of sphingolipids? (A) They all contain a fatty acid joined to glycerol. (B) They all contain a long-chain alcohol joined to isoprene. (C) They all contain ceramide joined to a polar group. (D) They all contain a carbohydrate joined to a phosphate group. (E) They all contain a polar head group and two non-polar fatty acids.

13. Which of these statements about triacylglycerol synthesis is correct? (A) Humans can store more energy in glycogen than in triacylglycerols. (B) Insulin stimulates conversion of dietary carbobydrate into triacylglycerols. (C) Triacylglycerols are the building blocks for cell membrane architecture. (D) Mammals are unable to convert carbohydrates into triacylglycerols. (E) Phosphatidic acid is not on the pathway of triacylglycerol synthesis.

14.What are the products of β oxidation of a saturated 20-carbon fatty acid? (A) 1 propionyl-CoA, 9 acetyl-CoA, 9 FADH2, and 9 NADH (B) 9 acetyl-CoA, 8 FADH2,8 NADH (C) 9 acetyl-CoA, 9 FADH2,9 NADH (D) 10 acetyl-CoA, 9 FADH2, 9 NADH (E) 10 acetyl-CoA, 10 FADH2, 10 NADH