In DNA replication, which enzyme synthesizes RNA primers?

Appeared in: INI-CET EXAM -2026

Explanation

Primase is a specific type of RNA polymerase that synthesizes short RNA sequences known as primers.
These RNA primers are crucial because DNA polymerases, the enzymes that build the new DNA strand, cannot initiate synthesis on their own (de novo).
The primer provides a free 3'-hydroxyl (-OH) group, which serves as the essential starting point for DNA polymerase III to begin adding deoxyribonucleotides and elongating the new DNA strand.

Option A: Topoisomerase manages the physical structure of DNA by relieving the torsional strain and supercoiling that occurs as the double helix is unwound. It does not synthesize any nucleic acid strands.
Option B: DNA polymerase II is primarily an enzyme involved in DNA repair pathways. It helps to correct errors or damage in the DNA but is not the main enzyme for either primer synthesis or bulk DNA replication.
Option C: DNA polymerase III is the main workhorse of DNA replication, responsible for synthesizing the majority of the new DNA strand. However, it can only add nucleotides to a pre-existing strand; it cannot initiate a new one.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Enzymes involved in DNA replication as background academic context rather than a clinical decision trigger.
A foundational understanding of DNA replication and its enzymes is essential for grasping the mechanisms of genetic inheritance, mutations, and many genetic disorders.
Many modern drugs, particularly in oncology and virology, target enzymes involved in DNA replication. For instance, some chemotherapy agents inhibit topoisomerases to prevent cancer cells from dividing, and antiviral drugs like Acyclovir target viral DNA polymerase.
What if? - If a cell had a non-functional primase due to a genetic mutation, DNA replication could not be initiated. This would be a lethal condition for the cell, as it would be unable to duplicate its genome and therefore unable to divide.

How to Approach the Question

This is a factual recall question testing knowledge of molecular biology.
First, identify the key process described in the question: the synthesis of RNA primers during DNA replication.
Next, systematically review the function of each enzyme listed in the options.
Topoisomerase: Manages DNA coiling.
DNA polymerase II: Primarily for DNA repair.
DNA polymerase III: The main DNA synthesizer, but requires a primer.

Concept Tested & Keywords

QzJQeADaSfFPDfq6WX-185

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 236-238

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 358-360

Practise the full INI-CET EXAM -2026

Attempt every question from this paper in a timed mock, then review the full solution for each one.