Mitochondrial DNA: Unique Features and Contribution to Disease

Introduction

Mitochondrial DNA (mtDNA) resides within mitochondria, cellular structures responsible for energy production through oxidative phosphorylation. Unlike nuclear DNA (nDNA), mtDNA exhibits distinct characteristics that influence its inheritance, mutation patterns, and role in various diseases. This blog post will explore the unique properties of mtDNA, its function within cells, and its link to human pathologies.

Structural and Functional Differences of mtDNA

  • Circular Structure: Unlike the linear chromosomes of nDNA, mtDNA is a small, circular molecule containing roughly 16,569 base pairs in humans. This compact structure encodes a limited set of genes (37 in humans) essential for mitochondrial function.
  • Maternal Inheritance: In contrast to the inheritance of nDNA from both parents, mtDNA is primarily inherited from the mother. Mitochondria are mainly localized within the oocyte cytoplasm, with minimal contribution from sperm during fertilization.
  • High Copy Number: Each cell houses numerous mitochondria, resulting in a much higher abundance of mtDNA molecules compared to nDNA.

Structure of mitochondrial DNA. Mammalian mitochondrial DNA (mtDNA) is a double-stranded circular DNA with approximately 16,000 base pairs. mtDNA is formed by a light strand and a heavy strand. Pink color bands denote tRNA coding sequences (there are 22 mitochondrial tRNAs, each are labeled by the respective amino acid code). Protein coding segments on mtDNA do not have introns and are transcribed by a single polycistronic mRNA from each strand. All protein coding sequences are marked in green color with respective gene name abbreviations. Abbreviations: Cyt b, Cytochrome b; ND, NADH dehydrogenase; CO, cytochrome c oxidase; and ATPase, ATP synthase. The two ribosomal (rRNAs) locations are marked, 12S and 16S RNAs. D-loop (grey color) region does not have coding sequences.

Increased Vulnerability to Mutations

  • Proximity to Reactive Oxygen Species (ROS): The electron transport chain within mitochondria generates ATP, the cell's energy currency, but also produces ROS (reactive oxygen species) as a byproduct. This constant exposure to oxidative stress elevates the mutation rate of mtDNA. Research is ongoing to explore potential solutions to mitigate ROS-induced mtDNA damage, offering promising avenues for future interventions.
  • Limited Repair Mechanisms: Mitochondria lack efficient DNA repair mechanisms compared to the nucleus, leading to a greater accumulation of mutations over time.

mtDNA and Disease Association

Mutations in mtDNA can cause a range of human diseases, often affecting tissues with high energy demands such as muscles, nerves, and the brain. The severity of the disease phenotype depends on several factors, including:

  • Mutation type and penetrance: The specific mtDNA mutation, its functional impact, and the percentage of mutated mtDNA molecules within a cell (heteroplasmy) influence disease presentation.
  • Mitochondrial threshold effect: A certain percentage of mutated mtDNA molecules within a cell is often required for clinical symptoms to manifest.

The role of mtDNA ( a ), nuclear DNA (nDNA) mutations ( b ) and ROS ( c ) in mitochondrial disease. Multiple factors diminish the integrity of mitochondria that lead to loss of cell function, apoptosis and ocular degeneration. a The most common mitochondrial diseases, e.g. LHON, result from primary mtDNA mutations that prevent successful completion of respiratory complexes , e.g. complex I, thus reducing mitochondrial oxidative phosphorylation (OXPHOS). b Mutations in nDNA-encoded mitochondrial proteins result in an impaired ability to undergo mtDNA replication, maintenance and mtDNA repair. c ROS, in particular superoxide

Examples of mtDNA-Associated Diseases

  • Leber hereditary optic neuropathy (LHON): This maternally inherited condition causes progressive vision loss due to mutations affecting mitochondrial complex I function.
  • MELAS (Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes): Mutations in mtDNA tRNAs can lead to MELAS, characterized by muscle weakness, seizures, and stroke-like episodes.
  • Mitochondrial Myopathies: A diverse group of muscle disorders can result from mtDNA mutations affecting oxidative phosphorylation complexes.

Conclusion

mtDNA, with its unique characteristics and susceptibility to mutations, plays a significant role in human health and disease. Understanding mtDNA biology is essential for developing diagnostic tools, treatment strategies, and potentially future genetic interventions for various currently untreatable mitochondrial disorders.

Learn more about how mitochondria contribute to health and disease in this video:


in News
Mitochondrial DNA: Unique Features and Contribution to Disease
Gen store May 31, 2024
Share this post
Tags
Our blogs
Archive
Sign in to leave a comment
H5N1 Mutations: Tracking and Predicting the Next Pandemic Threat