AIIMS CRE, SNO-2024: Which DNA polymerase is responsible for replicating mitochondrial DNA in eukaryotes?

AIIMS CRE, SNO-2024

Pathology & Genetics

Easy

Appeared in: AIIMS CRE, SNO-2024

Explanation

DNA Polymerase gamma (Pol γ) is the only DNA polymerase located in the mitochondria of eukaryotic cells.
Its primary and exclusive function is the replication and repair of the mitochondrial DNA (mtDNA) genome.
Unlike nuclear DNA which uses multiple polymerases, the entire process of mtDNA replication is managed by Pol gamma.
This specialization makes it distinct from other polymerases like alpha, beta, and delta, which function within the nucleus.

Option A: Pol alpha functions in the nucleus, not the mitochondria. Its main role is to initiate DNA replication by synthesizing an RNA primer.
Option B: Pol beta is a nuclear enzyme primarily involved in DNA repair, specifically base excision repair (BER), not replication of mitochondrial DNA.
Option D: Pol delta operates in the nucleus and is the principal enzyme for synthesizing the lagging strand during nuclear DNA replication.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Function of Eukaryotic DNA Polymerases as background academic context rather than a clinical decision trigger.
Understanding the function of Pol gamma is crucial for diagnosing mitochondrial diseases. Mutations in the POLG gene, which codes for Pol gamma, are a common cause of inherited mitochondrial disorders, leading to conditions like Alpers' syndrome, myopathies, and progressive external ophthalmoplegia.
Certain antiviral drugs, particularly some nucleoside reverse transcriptase inhibitors (NRTIs) used to treat HIV, can inhibit Pol gamma. This inhibition leads to mitochondrial toxicity, causing side effects like peripheral neuropathy, pancreatitis, and lactic acidosis.
What if? If a patient on long-term NRTI therapy develops muscle weakness and elevated lactate levels, a nurse should suspect mitochondrial toxicity due to Pol gamma inhibition and report it promptly, as it may require a change in medication.

How to Approach the Question

First, identify the core components of the question: the process is 'replicating DNA' and the specific location is 'mitochondrial DNA' in 'eukaryotes'.
This is a factual recall question requiring knowledge of molecular biology.
Systematically review the functions of the listed DNA polymerases (Pol alpha, beta, gamma, delta).
Recall or deduce the cellular location for each polymerase's primary function. Pol alpha, beta, and delta are known to be active in the nucleus for replication and repair.
Identify the polymerase that is specifically associated with the mitochondria. Pol gamma is uniquely responsible for mitochondrial DNA.
Select the option that matches this specific function and location.

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 237-238

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