Mitochondria function and dysfunction

Mitochondria are often referred to as the "powerhouses" of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP), which is used as a source of chemical energy. They have several key functions:

1. ATP Production: The primary function of the mitochondria is to produce energy in the form of ATP through the process of oxidative phosphorylation. This involves a series of enzymatic reactions in the electron transport chain, located in the inner mitochondrial membrane. Electrons are transferred from molecules of nutrients to oxygen molecules, creating a flow of electrons that allows for the generation of ATP.

2. Calcium Storage: Mitochondria play a role in calcium homeostasis, which is critical for several cellular processes, including signal transduction, muscle contraction, and neurotransmitter release.

3. Apoptosis (Programmed Cell Death): Mitochondria have a role in initiating apoptosis. They release factors that activate the enzymes responsible for cell death when a cell is damaged or stressed beyond repair.

4. Regulation of the Cell Cycle and Cell Growth: Mitochondria are involved in several aspects of cell cycle regulation, including the initiation of DNA replication and the transition between different phases of the cell cycle.

5. Metabolism: Mitochondria are involved in various metabolic pathways, such as the citric acid cycle (also known as the Krebs cycle or TCA cycle), beta-oxidation of fatty acids, and the metabolism of amino acids.

6. Thermogenesis: In brown adipose tissue, mitochondria help generate heat through a process called non-shivering thermogenesis. The protein responsible for this is called thermogenin or uncoupling protein (UCP).

7. Steroid Synthesis: Mitochondria in certain cells (e.g., adrenal gland cells) are involved in the synthesis of steroids, such as cortisol and aldosterone.

8. Production of Reactive Oxygen Species (ROS): While mitochondria primarily produce ATP, this process can also generate ROS, which can be damaging to cells if not properly managed. Cells have antioxidant systems to mitigate the harmful effects of ROS. Drugs as well as endogenous antioxidants such as superoxide dismutase (SOD), peroxidase, glutathione (GSH) and vitamin E have been discovered to eliminate the ROS.

9. Mitochondrial DNA (mtDNA) Replication and Transcription: Unlike other organelles, mitochondria have their own DNA. They can replicate, transcribe, and translate some of their own proteins.
   Mitochondrial DNA is the circular chromosome found inside the cellular organelles called mitochondria. Located in the cytoplasm, mitochondria are the site of the cell's energy production and other metabolic functions. Offspring inherit mitochondria — and as a result mitochondrial DNA — from their mother.

The proper functioning of mitochondria is crucial for the health and survival of the cell. Dysfunctions in mitochondria have been implicated in a variety of diseases, including neurodegenerative diseases, cardiovascular diseases, and mitochondrial disorders.

Cause of mitochondria dysfunction

Mitochondrial dysfunction refers to a condition where the mitochondria are not working properly, leading to reduced ATP production, increased production of reactive oxygen species (ROS), or other disturbances in the cell.

The causes of mitochondrial dysfunction can be multifaceted and can arise due to:

1. Genetic mutations: Mutations in mitochondrial DNA (mtDNA) or in nuclear DNA that encodes mitochondrial proteins can cause mitochondrial diseases. These mutations can be inherited or can arise spontaneously. For instance, Leber's hereditary optic neuropathy (LHON) is a form of inherited mitochondrial disease that primarily affects males and leads to vision loss.

2. Environmental factors: Exposure to certain drugs, toxins, or chemicals can interfere with mitochondrial function. For instance, some medications, like certain antibiotics or chemotherapy drugs, can cause mitochondrial toxicity.

3. Aging: Mitochondrial function naturally declines with age. The accumulation of mutations in mtDNA, damage from ROS, and other factors associated with aging can lead to decreased mitochondrial efficiency.

4. Oxidative stress: An imbalance between the production of ROS and the cell's ability to detoxify these reactive intermediates can damage mitochondria. Excessive ROS can damage mitochondrial lipids, proteins, and DNA.

5. Inadequate nutrient supply: Certain nutrients are crucial for mitochondrial function, such as coenzyme Q10, magnesium, and B vitamins. A deficiency in these can impair mitochondrial function.

6. Diseases: Conditions like diabetes, neurodegenerative diseases (Parkinson's, Alzheimer's), and heart diseases are associated with mitochondrial dysfunction.

7. Mitochondrial dynamics: Mitochondria constantly undergo fusion (joining together) and fission (splitting apart). Disruptions in these processes can lead to dysfunction.

8. Impaired mitophagy: Mitophagy is the process of removing damaged mitochondria from the cell. If this process is hindered, damaged and malfunctioning mitochondria can accumulate in the cell.

It's important to note that while mitochondrial dysfunction can contribute to disease processes, it may not necessarily be the primary cause. Often, it is a combination of genetic, environmental, and cellular factors that culminate in mitochondrial dysfunction.

Read: "Study reveals how SARS-CoV-2 alters mitochondria, leading to energy outages and organ failure"