Question

You have discovered an 'Exo mutant form of DNA polymerase in which the 3'-to-5' exonuclease function has been destroyed, but the ability to join nucleotides together is unchanged. Which of the following properties do you expect the mutant polymerase to have?

a. It will polymerize in both the 5'-to-3' direction and the 3'-to-5' direction.
b. It will polymerize more slowly than the normal Exo+ polymerase.
c. It will fall off the template more frequently than the normal Exo+ polymerase.
d. It will be more likely to generate mismatched base pairs.

Answer 1

The Exo mutant form of DNA polymerase, which lacks the 3'-to-5' exonuclease function, will be more likely to generate mismatched base pairs during DNA replication due to the absence of the proofreading ability.

Step-by-step explanation:

When a DNA polymerase has its 3'-to-5' exonuclease function, which is responsible for proofreading, destroyed, but retains its ability to join nucleotides together, we can expect certain properties to be affected. In this scenario, the most likely outcome is that the mutant polymerase will be more prone to incorporating mismatched base pairs during DNA replication. This mutant form of the enzyme lacks the critical proofreading function that normally corrects mistakenly incorporated nucleotides immediately after they are added. Without this error-correcting capability, the enzyme will not be able to remove incorrectly paired bases, leading to a higher rate of replication errors.

The DNA polymerase reads the template strand in the 5'-to-3' direction and adds nucleotides in only the 3'-to-5' direction. While normal DNA polymerase can quickly correct mistakes by reversing its action and excising the incorrectly paired nucleotides, the Exo mutant form cannot. Therefore, answer (d) 'It will be more likely to generate mismatched base pairs' is the property we expect from the mutant polymerase.