Question

On average, errors occur in DNA synthesis only once in every ten billion nucleotides incorporated. Which of the following does NOT contribute to this high fidelity of DNA synthesis? (A) Complementary base-pairing between the nucleotides (B) Tightening of the DNA polymerase around its active site to ensure correct pairing before monomer incorporation (C) Proofreading by the 3'-to-5' exonuclease activity of the enzyme to correct mispairing even after monomer incorporation (D) A strand-directed mismatch repair system that detects and resolves mismatches soon after DNA replication (E) None of the above

Answer 1

All the mechanisms provided in options A to D contribute to the high fidelity of DNA synthesis by ensuring correct base pairing, proofreading newly added nucleotides, and repairing mismatches post-replication. Among the options provided, the one that does NOT contribute to this process is (E) None of the above.

Step-by-step explanation:

The high fidelity of DNA synthesis is attributed to several key mechanisms. Firstly, complementary base-pairing ensures that each new nucleotide is correctly matched with its opposite base on the template strand. Secondly, DNA polymerase tightens around its active site which helps confirm correct pairing before incorporating the monomer. Thirdly, proofreading activity, particularly the 3'-to-5' exonuclease function of DNA polymerases, catches and corrects any mispairing even after monomer incorporation. Lastly, the mismatch repair system acts post-replication to find and repair any remaining mispaired nucleotides.

Among the options provided, the one that does NOT contribute to this process is (E) None of the above. This is because all the listed mechanisms (A-D) are indeed involved in maintaining the high accuracy of DNA synthesis.

Answer 2

(E) None of the above

Step-by-step explanation:

All of the answers contribute to the high fidelity of DNA synthesis.

Accuracy of the DNA replication is achieved thanks to various mechanisms such as:

• DNA polymerase activity (high processivity)-ability of the enzyme to copy long stretches of DNA
• DNA polymerase proofreading-ability to recognize its own mistakes and fix them
• Cell's surveillance-cell monitors its DNA status, checks for the damage
• Mismatch Repair-cell contain repair machinery which recognizes DNA helix deformities, removes and replaces the portion containing the mismatch etc.