Question

DNA Polymerase I molecule contains how many active sites?

• A. Two
• B. Three
• C. Four
• D. One

Hint:

DNA Polymerase I has three important activities: polymerase activity, proofreading exonuclease activity, and primer-removing exonuclease activity.

Answer 1

The Correct Option is B

Concept:
DNA Polymerase I is an important enzyme involved in DNA replication and DNA repair in prokaryotes. It has multiple enzymatic activities.

Step 1: Identify the functions of DNA Polymerase I.
DNA Polymerase I has three major activities: \[ 1. \quad 5' \rightarrow 3' \text{ polymerase activity} \] \[ 2. \quad 3' \rightarrow 5' \text{ exonuclease activity} \] \[ 3. \quad 5' \rightarrow 3' \text{ exonuclease activity} \]

Step 2: Understand polymerase activity.
The polymerase activity adds nucleotides to the growing DNA strand in the \(5' \rightarrow 3'\) direction.

Step 3: Understand proofreading activity.
The \(3' \rightarrow 5'\) exonuclease activity removes incorrectly added nucleotides. This provides proofreading ability.

Step 4: Understand primer removal activity.
The \(5' \rightarrow 3'\) exonuclease activity removes RNA primers during DNA replication and helps in repair processes.

Step 5: Count the active sites.
Since DNA Polymerase I has three functional enzymatic activities, it is considered to have three active sites. \[ \therefore \text{Correct Answer is (B)} \]