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Mitochondria
Context:
A study has found that mitochondria in our brain cells often transfer their DNA into the nucleus, where it gets integrated into the cells’ chromosomes.
Mitochondrial DNA behaves like a virus:
- Mitochondria, present in all our cells, have their own DNA—a small circular strand with about three dozen genes—unlike other organelles.
- In recent decades, researchers have discovered that mitochondrial DNA has occasionally “jumped” out of the organelle and integrated into human chromosomes.
- Mitochondrial DNA behaves similarly to a virus, using cuts in the genome to insert itself, or like retrotransposons that move around within the human genome.
About Mitochondria:
Mitochondria are essential organelles found in nearly all eukaryotic cells, often referred to as the “powerhouses of the cell” due to their primary role in generating adenosine triphosphate (ATP), the energy currency of the cell.
Structure of Mitochondria:
- Mitochondria have a unique double-membrane structure, which consists of:
- Outer Membrane: This membrane is smooth and contains proteins called porins that allow the passage of small molecules and ions.
- Inner Membrane: This membrane is highly folded into structures known as cristae, which increase the surface area for chemical reactions.
- It is impermeable to most ions and small molecules, with specific transport proteins facilitating the movement of substances.
- Intermembrane Space: The space between the outer and inner membranes.
- Matrix: The innermost compartment, which contains enzymes, mitochondrial DNA (mtDNA), ribosomes, and various substrates for metabolic processes.
Functions of Mitochondria:
- ATP Production: Through oxidative phosphorylation, mitochondria generate ATP by using energy derived from the electron transport chain, which is fueled by nutrients.
- Regulation of Metabolism: Mitochondria are involved in various metabolic pathways, including the citric acid cycle (Krebs cycle) and fatty acid oxidation.
- Calcium Homeostasis: They help regulate intracellular calcium levels, which is crucial for various cellular processes, including signalling and muscle contraction.
- Apoptosis: Mitochondria release cytochrome c and other factors that trigger programmed cell death (apoptosis), playing a key role in maintaining cellular health.
- Heat Production: In brown adipose tissue, mitochondria can generate heat through non-shivering thermogenesis, which is important for thermoregulation.
- Reactive Oxygen Species (ROS) Signalling: Mitochondria produce ROS as byproducts of ATP production, which can act as signalling molecules but also contribute to cellular damage if not regulated.
Mitochondrial Genetics:
- Mitochondria contain their own circular DNA (mtDNA), which is inherited maternally.
- This DNA encodes 13 proteins essential for the function of the respiratory chain, along with tRNAs and rRNAs required for mitochondrial protein synthesis.
- The presence of mtDNA supports the endosymbiotic theory, suggesting that mitochondria originated from free-living prokaryotes that entered into a symbiotic relationship with ancestral eukaryotic cells.
Mitochondrial Dysfunction and Disease:
- Metabolic Disorders: Conditions like diabetes and obesity can be linked to mitochondrial inefficiency.
- Neurodegenerative Diseases: Disorders such as Parkinson’s and Alzheimer’s disease have been associated with mitochondrial dysfunction.
- Mitochondrial Diseases: Genetic mutations affecting mitochondrial function can lead to a range of mitochondrial diseases, affecting energy production and leading to symptoms in multiple organ systems.