Which DNA polymerase is responsible for replicating mitochondrial DNA in eukaryotes?

Appeared in: AIIMS CRE, SNO-2024

Explanation

DNA Polymerase gamma (Pol γ) is the only DNA polymerase found in the mitochondria of eukaryotic cells.
Its exclusive function is to replicate and repair the mitochondrial DNA (mtDNA), a small circular chromosome.
Unlike nuclear DNA replication which involves multiple polymerases, mitochondrial DNA maintenance is entirely dependent on Pol gamma.

Option A: Pol alpha functions in the nucleus, where it initiates DNA replication by synthesizing RNA primers. It is not involved with mitochondrial DNA.
Option B: Pol beta is a nuclear enzyme whose primary role is in DNA repair, specifically base excision repair (BER). It does not replicate mitochondrial DNA.
Option D: Pol delta is a major replicative polymerase in the nucleus, responsible for synthesizing the lagging strand during chromosomal DNA replication. It has no function in the mitochondria.

Visual 1: Diagram - A diagram of a eukaryotic cell highlighting the nucleus and a mitochondrion. Arrows should point to the nucleus for Pol α, β, and δ, and to the mitochondrion for Pol γ, illustrating their distinct locations and primary functions.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Functions of Eukaryotic DNA Polymerases as background academic context rather than a clinical decision trigger.
Mutations in the POLG gene, which encodes for DNA Polymerase gamma, are a significant cause of inherited mitochondrial diseases. These disorders can affect multiple organ systems, particularly those with high energy demands like the brain, muscles, and liver.
Examples of POLG-related disorders include Alpers' syndrome (a progressive neurodegenerative disorder in children), progressive external ophthalmoplegia (PEO), and sensory ataxic neuropathy, dysarthria, and ophthalmoparesis (SANDO).
What if the question asked about the primary polymerase for the leading strand in the nucleus? The answer would be DNA Polymerase epsilon (Pol ε), which works in concert with Pol delta on the lagging strand.

How to Approach the Question

First, identify the key terms in the question: 'DNA polymerase' and 'mitochondrial DNA'.
This is a factual recall question that tests knowledge of cellular biology and enzyme function.
Recall the different types of eukaryotic DNA polymerases and their specific locations and roles within the cell.
Differentiate between polymerases that function in the nucleus (α, β, δ, ε) and the one that functions in the mitochondria.
The unique association of 'gamma' with 'mitochondria' is a key piece of information to remember. Select the option that matches this specific function.

Concept Tested & Keywords

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Practise the full AIIMS CRE, SNO-2024

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