Main functions:
1. Energy conversion
Mitochondria are places where eukaryotes carry out oxidative metabolism, and are places where sugars, fats and amino acids are finally oxidized to release energy. Mitochondria are responsible for the final oxidation through tricarboxylic acid cycle and oxidative phosphorylation, which correspond to the second and third stages of aerobic respiration respectively.
2. Every molecule of pyruvate produced in glycolysis of tricarboxylic acid cycle
will be actively transported across mitochondrial membrane. After entering the mitochondrial matrix, pyruvate will be oxidized and combined with coenzyme A to produce CO2, reduced coenzyme I and acetyl coenzyme A..
acetyl coenzyme a is the primary substrate of tricarboxylic acid cycle (also called "citric acid cycle" or "Krebs cycle"). The enzymes involved in this cycle are all free in the mitochondrial matrix except succinate dehydrogenase located in the inner membrane of mitochondria.
in the tricarboxylic acid cycle, every molecule of acetyl-CoA is oxidized, and at the same time, the reduction cofactors (including 3 molecules of NADH and 1 molecule of FADH2) and 1 molecule of guanosine triphosphate (GTP) of the initial electron transfer chain are produced.
3, oxidative phosphorylation
Reductive molecules such as p>NADH and FADH2 (the reduction equivalent in the cytoplasm matrix can enter the electron transfer chain from the malic acid-aspartic acid shuttle system composed of reverse transporters or through the phosphoglyceryl shuttle) undergo several reactions in the electron transfer chain to finally reduce oxygen and release energy, some of which is used to generate ATP and the rest is dissipated as heat energy.
the enzyme complexes (NADH- ubiquinone reductase, ubiquinone-cytochrome c reductase, cytochrome c oxidase) on the inner membrane of mitochondria pump protons into the gap of mitochondrial membrane by using the energy released in the process.
Although this process is efficient, there are still a few electrons that will prematurely reduce oxygen and form reactive oxygen species (ROS) such as superoxide, which can cause oxidative stress and degrade mitochondrial performance.
When protons are pumped into the gap between mitochondrial membranes, an electrochemical gradient is established on both sides of the inner membrane of mitochondria, and protons tend to diffuse along the concentration gradient. The only diffusion channel for protons is ATP synthase (respiratory chain complex V).
when protons return to the mitochondrial matrix from the membrane gap through the complex, the electric potential energy is used by ATP synthase to synthesize ATP from ADP and phosphoric acid. This process is called "chemical infiltration", which is an assisted diffusion.
Peter Mitchell won the Nobel Prize in 1978 for putting forward this hypothesis. In 1997, Nobel Prize winners Paul Boyer and John Wark clarified the mechanism of ATP synthase.
4, storing calcium ions
Mitochondria can store calcium ions, and can cooperate with endoplasmic reticulum, extracellular matrix and other structures to control the dynamic balance of calcium ion concentration in cells. The ability of mitochondria to quickly absorb calcium ions makes it a buffer zone for calcium ions in cells.
driven by the membrane potential of mitochondrial inner membrane, calcium ions can be transported into mitochondrial matrix by one-way carriers existing in mitochondrial inner membrane; When the mitochondrial matrix is excreted, it needs the assistance of sodium-calcium exchange protein or calcium-induced-calcium-release (CICR) mechanism.
When calcium ion is released, it will cause a "calcium wave" accompanied by a large change in membrane potential, which can activate some second messenger system proteins and coordinate the release of neurotransmitters in synapses and the secretion of hormones in endocrine cells. Mitochondria are also involved in calcium signal transduction during apoptosis.
Extended information:
mitochondrion is an organelle that exists in most cells and is covered by two membranes. It is a structure that produces energy in cells and is the main place for cells to carry out aerobic breathing, so it is called "power house". Its diameter is about .5 to 1. microns.
Except for Entamoeba histolytica, Giardia lamblia and several microsporidia, most eukaryotic cells have mitochondria to some extent, but their own mitochondria are different in size, quantity and appearance.
Mitochondria have their own genetic material and genetic system, but their genome size is limited, and they are semi-autonomous organelles. In addition to providing energy for cells, mitochondria also participate in processes such as cell differentiation, cell information transmission and cell apoptosis, and have the ability to regulate cell growth and cell cycle.
Reference: Baidu Encyclopedia-Mitochondria