Question

Which of the following lacks 3'-5' exonuclease activity?

a) Short fragment of DNA polymerase I
b) Taq DNA polymerase
c) T4 DNA ligase
d) None of the above

Answer 1

Taq DNA polymerase lacks 3'-5' exonuclease activity. This activity is responsible for proofreading during DNA replication and is present in DNA polymerase I but not in Taq DNA polymerase, which is often used in PCR.

Step-by-step explanation:

The enzyme which lacks 3'-5' exonuclease activity is Taq DNA polymerase. The 3'-5' exonuclease activity is important for proofreading during DNA replication to ensure the accuracy of DNA synthesis. Taq DNA polymerase is commonly used in PCR (Polymerase Chain Reaction) but lacks this proofreading ability, hence it cannot correct errors that occur during DNA synthesis.

DNA polymerase I, in contrast, does possess 3'-5' exonuclease activity; this is the part of the enzyme that is responsible for proofreading and removing mismatches. DNA ligase is crucial in the DNA replication process as well, but it functions to join DNA fragments together, an action distinct from the exonuclease activity of DNA polymerases.