mitochodriach

Mitochondria are membrane-bound organelles found in the cytoplasm of most eukaryotic cells. They are the primary sites of adenosine triphosphate (ATP) production through aerobic respiration and also participate in signaling, metabolism, and programmed cell death.

Structurally, mitochondria have a double membrane system: an outer membrane and a highly folded inner membrane that forms cristae. The space inside the inner membrane is the matrix, which contains enzymes of the Krebs cycle, mitochondrial DNA (mtDNA), and ribosomes. Mitochondrial DNA is typically a small circular genome inherited maternally in many organisms and encodes a subset of proteins essential for the respiratory chain.

Functionally, mitochondria convert energy from nutrient molecules into ATP. Pyruvate from glycolysis enters the mitochondrion and is converted to acetyl-CoA, feeding the Krebs cycle in the matrix. Electrons are transferred through the respiratory chain on the inner membrane, pumping protons to create a gradient that drives ATP synthesis via ATP synthase. In addition to energy production, mitochondria regulate calcium storage, generate heat in brown adipose tissue through uncoupling proteins, and can initiate apoptosis in response to cellular stress.

Evolutively, mitochondria are believed to have originated from endosymbiotic bacteria, inferred from features such as their circular DNA, bacterial-like ribosomes, and double membranes. Clinically, defects in mitochondrial genes or nuclear genes encoding mitochondrial proteins can cause mitochondrial diseases with variable symptoms, often influenced by heteroplasmy, the coexistence of normal and mutant mtDNA within a cell.