Mitochondrion

A mitochondrion is an organelle found within most eukaryotic cells, responsible for generating energy through aerobic respiration. Often referred to as the "powerhouse of the cell," mitochondria are integral to cell metabolism and energy production.

Discovery and Significance

• Discovered by Albert von Kölliker in 1857.
• Term "mitochondrion" coined by Carl Benda in 1898.
• Popularized as "powerhouse of the cell" by Philip Siekevitz in 1957.
• Some multicellular organisms have cells lacking mitochondria, e.g., mature mammalian red blood cells.
• Involved in significant human disorders and diseases.

Structure

Mitochondria have a complex structure including:

• Outer Membrane: Encloses the organelle, containing porins and various enzymes.
• Intermembrane Space: Between the outer and inner membranes, with similar small molecule concentrations as the cytosol.
• Inner Membrane: Houses proteins responsible for ATP production via the electron transport chain.
• Cristae: Infoldings of the inner membrane that increase surface area for ATP production.
• Matrix: Contains enzymes for the citric acid cycle and mitochondrial DNA.

Functions

1. Energy Conversion:

   • Primary role in ATP production through the citric acid cycle & oxidative phosphorylation.
   • Pyruvate from glycolysis enters citric acid cycle; generates NADH and FADH2 for electron transport.

2. Heat Production:

   • Mitochondrial uncoupling can produce heat instead of ATP.

3. Other Functions:

   • Fatty acid synthesis, calcium ion regulation, cellular proliferation regulation, programmed cell death.

Mitochondrial Genetics

• Contains its own genome, similar to bacterial genomes.
• Genetic studies support endosymbiotic theory - mitochondria evolved from free-living prokaryotes.
• Human mitochondrial genome includes 37 genes for essential functions.

Dysfunction and Disease

• Mitochondrial diseases often manifest as neurological disorders.
• Links to conditions such as autism, cardiac dysfunction, and aging.
• Mitochondrial DNA mutations lead to disorders like Leber's hereditary optic neuropathy.

Evolution

• Endosymbiotic theory widely accepted as the origin of mitochondria.
• Mitochondria likely evolved from proteobacteria.
• Some unicellular eukaryotes have mitochondrion-related organelles instead.

Additional Functions

• Mitochondria play roles in signaling, cellular differentiation, and apoptosis.
• Interaction with endoplasmic reticulum, forming mitochondria-associated ER membranes (MAM).

Historical Context

• Initial observations by Kölliker in 1857; term "bioblasts" introduced by Altmann in 1890.
• The development of high-resolution electron micrographs in 1952 advanced mitochondrial research.

See Also

• Anti-mitochondrial antibodies
• Mitochondrial genetic studies
• Mitochondrial diseases and their impact on health

Overall, mitochondria are critical for cellular energy production and have roles in many physiological processes. Studying mitochondria helps understand various genetic disorders and their impact on human health.