mitochondrial DNA replication

Definition

Target type: biologicalprocess

The process in which new strands of DNA are synthesized in the mitochondrion. [GOC:ai]

Mitochondrial DNA (mtDNA) replication is a complex process that occurs within the mitochondria, the powerhouses of the cell. Unlike nuclear DNA, which replicates during the S phase of the cell cycle, mtDNA replication is continuous and independent of the nuclear cycle. It involves a series of steps, including:

**1. Initiation:** Replication begins at a specific origin of replication, called OriL, located within the displacement loop (D-loop) region of the mtDNA molecule.

**2. Strand Separation and Elongation:** The two strands of the mtDNA molecule separate, and a replication fork is formed. One strand, the heavy strand (H-strand), is replicated continuously using the leading strand mechanism, while the other strand, the light strand (L-strand), is replicated discontinuously using the lagging strand mechanism.

**3. Replication of the Heavy Strand:** The H-strand is replicated using a polymerase called DNA polymerase γ (Pol γ), which is specific to mtDNA. The replication of the H-strand continues around the circular molecule until it reaches the end of the L-strand.

**4. Replication of the Light Strand:** The L-strand replication is initiated at a second origin, called OriH, located within the D-loop region. This strand is replicated discontinuously in short fragments called Okazaki fragments, which are later joined together by DNA ligase.

**5. Termination:** Replication terminates when the H-strand replication fork encounters the OriH region, and the L-strand replication fork encounters the OriL region.

**6. Mitochondrial DNA Integrity and Repair:** mtDNA replication is subject to error, but there are mechanisms in place to ensure the fidelity and integrity of the replicated DNA. Specialized DNA repair mechanisms are in place to correct errors that occur during replication.

**7. mtDNA Replication Regulation:** The process of mtDNA replication is tightly regulated to ensure that the number of mitochondria and their DNA content are appropriate for the cell's energy needs. This regulation involves a complex interplay of transcription factors, regulatory proteins, and metabolic signals.

**The key enzymes involved in mtDNA replication are:**

* **DNA polymerase γ (Pol γ):** The primary polymerase responsible for replicating both the H-strand and L-strand.
* **mtSSB:** A single-stranded DNA-binding protein that stabilizes the single-stranded DNA during replication.
* **mtDNA helicase:** Unwinds the double-stranded DNA to allow for strand separation.
* **DNA ligase:** Joins the Okazaki fragments together during L-strand replication.
* **RNase H1:** Removes the RNA primers used during L-strand replication.

mtDNA replication is essential for cellular function, as it provides the genetic information for the production of essential proteins involved in oxidative phosphorylation, the process that generates ATP, the primary energy source of the cell. Mutations in mtDNA can lead to a variety of human diseases, including mitochondrial diseases, which are characterized by defects in energy production and can affect multiple organs and tissues.'
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Proteins (3)

Compounds (8)