Question

Given below are two statements:
Statement (I): DNA polymerase I is a single polypeptide of molecular weight 199,000.
Statement (II): DNA polymerase III holoenzyme has a molecular mass of about 988,000 daltons.
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

DNA Polymerase I is a relatively small, single-subunit enzyme (\(\approx 109\text{ kDa}\)).
DNA Polymerase III is a massive, multi-subunit holoenzyme complex (\(\approx 988\text{ kDa}\)) responsible for synthesizing the bulk of the new DNA strands.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
DNA polymerases are the primary enzymes responsible for synthesizing new DNA strands during replication in *Escherichia coli*.
These enzymes differ significantly in their subunit composition, molecular mass, and specific enzymatic activities.

Step 2: Detailed Explanation:
Let us evaluate both statements:
Statement (I) is incorrect.
DNA polymerase I in *E. coli* is a single polypeptide chain with a molecular weight of approximately \( 103,000 \) to \( 109,000 \) daltons (not \( 199,000 \) daltons).
It plays a major role in removing RNA primers and filling the gaps during replication and repair.
Statement (II) is correct.
DNA polymerase III is the primary replicative enzyme complex in *E. coli*.
The functional enzyme exists as a large multiprotein complex called the DNA polymerase III holoenzyme.
This holoenzyme consists of ten different types of subunits organized into a dimeric structure, with a total molecular mass of approximately \( 900,000 \) to \( 988,000 \) daltons.
Therefore, Statement (I) is false, but Statement (II) is true.

Step 3: Final Answer:
Statement (I) is incorrect but Statement (II) is correct.