Question

List other types of errors that occur during replication of DNA.7. Explain why the formation of mismatched base pairs during replication can cause a mutation.

Answer 1

1. DNA replication errors can occur either by small insertion or deletions or due to point mutations. Base pair substitution mutation can result from wobble pairing. It happens due to incorrect partner between the base pairs due to different spatial positioning of the atoms involved in H-bonding. For example a GC-AT transition. Addition or deletion can occur spontaneously during replication. Insertion and deletion in structural genes generate frameshift mutations. If DNA polymerase add untemplated base, new DNA looping occurs, resulting in addition mutation.

2. DNA mismatches arise from errors during DNA replication. Mispairing occurs during DNA synthesis because keto-enol and amino-imino tautomeric forms occasionally cause mismatching during the base-pairing process.These mismatches would result in a mutation if they were not detected and corrected by a process called proofreading. Both DNA polymerases I and III proofread base-pair mismatches because any base pairs other than adenosine-thymine (AT) and guanine-cytosine (GC) create an irregularity in the shape of the DNA helix. As the helix is synthesized, it passes through a channel in the DNA polymerase enzymes that requires a precise fit. Any irregularity in the helix results in the activation of a 3′ to 5′ exonuclease activity in both DNA polymerase enzymes. In other words, the polymerase backs up (3′ to 5′ direction), removes the incorrect nucleotide, and then reinserts the correct nucleotide.