Question

Enzyme required for removing RNA primer during DNA replication is

• A. DNA primase
• B. Endonucleases
• C. DNA Polymerase III
• D. DNA Polymerase I

Hint:

In eukaryotic cells, RNA primers are removed by a different mechanism involving RNase H (which degrades the RNA strand of RNA-DNA hybrids) and Flap Endonuclease 1 (FEN1).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
DNA replication requires short RNA primers synthesized by DNA primase to provide a free 3'-OH group for DNA polymerase to begin synthesis.
On the lagging strand, DNA is synthesized in short fragments called Okazaki fragments, each starting with an RNA primer.
These RNA primers must be removed and replaced with DNA to form a continuous DNA strand.

Step 2: Detailed Explanation:
In *Escherichia coli*, DNA Polymerase I plays a central role in removing RNA primers during replication.
Unlike other DNA polymerases, DNA Polymerase I possesses a unique 5' to 3' exonuclease activity in addition to its 5' to 3' polymerase and 3' to 5' proofreading exonuclease activities.
As DNA Polymerase I binds to the nick between the newly synthesized Okazaki fragment and the preceding RNA primer, it uses its 5' to 3' exonuclease activity to degrade the RNA primer in front of it.
At the same time, it uses its 5' to 3' polymerase activity to synthesize a complementary DNA strand, filling the resulting gap behind it.
This coordinated process is called nick translation.
Let us review the other options:
- DNA primase synthesizes the RNA primers but does not remove them.
- DNA Polymerase III is the primary replicative polymerase responsible for elongating both the leading and lagging strands, but it lacks the 5' to 3' exonuclease activity needed to remove RNA primers.
- Endonucleases cleave phosphodiester bonds within a polynucleotide chain, but do not selectively remove replication primers.

Step 3: Final Answer:
The enzyme required for removing the RNA primer is DNA Polymerase I, corresponding to option (D).