1, energy conversion
Mitochondria is the place where eukaryotes undergo oxidative metabolism, and it is also the place where sugar, fat and amino acids are finally oxidized to release energy. Mitochondria are responsible for final oxidation through tricarboxylic acid cycle and oxidative phosphorylation, which correspond to the second and third stages of aerobic respiration respectively.
2. Tricarboxylic acid cycle
Every pyruvate molecule produced in glycolysis will be actively transported across the mitochondrial membrane. After entering the mitochondrial matrix, pyruvate will be oxidized and combined with coenzyme A to produce CO2, reduced coenzyme A and acetyl coenzyme A. ..
Acetyl coenzyme A is the primary substrate of tricarboxylic acid cycle (also known as "citric acid cycle" or "Krebs cycle"). Except succinate dehydrogenase located in the inner membrane of mitochondria, all the enzymes involved in this cycle are free from the mitochondrial matrix.
In the tricarboxylic acid cycle, every molecule of acetyl coenzyme A is oxidized, and at the same time, the reduction cofactors of the initial electron transfer chain (including 3 molecules of NADH and 1 molecule of FADH2) and 1 molecule of guanosine triphosphate (GTP) are generated.
3. Oxidative phosphorylation
Reducing molecules, such as NADH and FADH2 (the reducing equivalent in the cytoplasm matrix can enter the electron transfer chain from malate-aspartic acid shuttle system composed of reverse transporters or through glycerophosphate shuttle function), undergo several reactions in the electron transfer chain, and finally reduce oxygen and release energy, some of which are used to produce ATP and the rest are dissipated in the form of heat energy.
The enzyme complexes (NADH- ubiquinone reductase, ubiquinone-cytochrome c reductase, cytochrome c oxidase) on the inner membrane of mitochondria use the energy released during the process to pump protons into the gap of mitochondrial membrane in reverse concentration gradient.
Although this process is efficient, a few electrons will prematurely reduce oxygen and form reactive oxygen species (ROS) such as superoxide, which will cause oxidative stress and reduce mitochondrial performance.
When protons are pumped into the gap of mitochondrial membrane, an electrochemical gradient is established on both sides of mitochondrial inner membrane, and protons tend to spread along the concentration gradient. The only diffusion channel of protons is ATP synthase (respiratory chain complex V).
When protons return to the mitochondrial matrix from the membrane gap through the complex, the potential energy is used by ATP synthase to synthesize ATP from ADP and phosphoric acid. This process is called "chemical infiltration" and is an auxiliary diffusion.
Peter Mitchell won the 1978 Nobel Prize for putting forward this hypothesis. 1997 nobel prize winners Paul Boyer and John Wark expounded the mechanism of ATP synthase.
Step 4 store calcium ions
Mitochondria can store calcium ions, and cooperate with endoplasmic reticulum and extracellular matrix to control the dynamic balance of intracellular calcium ion concentration. Mitochondria's ability to quickly absorb calcium ions makes it a buffer zone for calcium ions in cells.
Driven by mitochondrial membrane potential, calcium ions can be transported to mitochondrial matrix through unidirectional carriers existing in mitochondrial membrane; When the mitochondrial matrix is excreted, sodium-calcium exchange protein or calcium-induced calcium release (CICR) mechanism is needed.
When calcium ion is released, it will cause "calcium wave" accompanied by great changes 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 data:
Mitochondria are organelles that exist in most cells and are covered by two membranes. It is the structure that produces energy in cells and the main place for cells to carry out aerobic breathing, so it is called "power room". Its diameter is about 0.5 to 65438 0.0 micron.
Except Entamoeba histolytica, Giardia lamblia and several microsporidia, most eukaryotic cells have mitochondria to some extent, but their own mitochondria are different in size, number and appearance.
Mitochondria have their own genetic material and genetic system, but the genome size is limited, and they are semi-autonomous organelles. Mitochondria not only provide energy for cells, but also participate in cell differentiation, cell information transmission and cell apoptosis, and have the ability to regulate cell growth and cell cycle.
Reference: Baidu Encyclopedia-Mitochondria