Errors in Replication

Sometimes during the course of replication the DNA polymerase makes a mistake and tries to pair two non-complementary bases. Most such errors are corrected. Here, the second base pair, thymine and guanine, is incorrect. The DNA polymerase usually detects the mistake, backs up one base and removes the mismatched nucleotide. It then resumes forward movement, inserts the correct base, and continues to replicate the template DNA strand. Because the polymerase moves in the 3’ to 5’ direction when it excises a mismatched nucleotide, the proofreading ability of the enzyme is called 3’ to 5’ exonuclease activity.

Question 1: What is the direction for DNA polymerase proofreading?
  1. 5' to 3'
  2. 3' to 5'
  3. 3 to 3'
  4. 5' to 5'

Answer 1

Answer - (b) 3' to 5'

Question 2: Which enzyme detects the errors in DNA replication and mismatched base pairs?
  1. Sythase
  2. Gyrase
  3. DNA polymerase
  4. Endonuclease

Answer 2

Answer - (c) DNA polymerase