Read DNA Enzymes by Their Reaction
Read DNA-enzyme questions by following the reaction: what is cut, removed, synthesised or resealed?
DNA Enzymes and Topology is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Keep polymerase I activities together
DNA polymerase I fills gaps after primer removal and has both 5′→3′ exonuclease activity and 3′→5′ proofreading activity. A claim that it has only the first exonuclease activity is false. Choose D.
Read a topoisomerase gel by lane
DNA alone remains compact and supercoiled. With topoisomerase, relaxed forms appear. When the drug is added, the broken/smeared pattern shows that cutting occurred but clean resealing failed. The drug inhibits or traps topoisomerase I during its repair-related reaction: choose D.
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- ✓Polymerase I has 5′→3′ primer-removal and 3′→5′ proofreading exonuclease activity.
- ✓Topoisomerase must reseal DNA after transient cleavage.
- ✓Compare each gel lane against its specific added component.
A drug-induced DNA smear is evidence of failed DNA handling, not proof that the enzyme was protected.
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