Electron transfer

Introduction
This is an important event that is part of cellular respiration, or respiratory chain. It releases energy, which is then used by ATP-synthase, capable of creating more than 100 ATP molecules in 1 second.

As part of the electron-transport chain, high-energy electrons are used, which were created during the Krebs cycle. They emerge from it in the form of NADH and FADH 2. Through these carriers, they are transported to a chain of enzymes embedded in the phospholipid bilayer of the inner mitochondrial membrane. Here, they are transferred together with other reduction equivalents (hydrogen protons) between individual enzyme carriers according to the increasing redox potential. The transfer of reducing equivalents is conditioned by the oxidation and reduction processes of individual redox carriers, among them are NAD-dependent dehydrogenases, flavoproteins, cytochromes(see below) and molecular oxygen. During these events, energy is obtained for the transfer of hydrogen protons H + from the mitochondrial matrix to the intermembrane space. The resulting higher concentration of hydrogen ions ( proton gradient ) subsequently enables the activity of ATP-synthase.

At the end of the electron transport chain, the electrons are transferred to oxygen gas molecules. At this stage, the electrons have already given up all their energy as they pass through the respiratory chain.

Cytochromes
As already mentioned, cytochromes are substances that transport electrons through the inner mitochondrial membrane, which they achieve through a cascade of mutual oxidation-reduction reactions .

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Cytochromes b, c 1, c, a, and 3 are involved in the respiratory chain, in this order according to the increasing redox potential, the specific value of which for a given cytochrome is mainly influenced by the composition of the protein part of the molecule .

Structure
These are hemoproteins (compound proteins that have a heme group attached to their chain ), therefore they contain iron capable of transitioning between the divalent and trivalent states, thanks to which they can participate in the transfer of electrons. Through an oxidation-reduction reaction with the previous link of the cascade, the cytochrome receives an electron, and the iron present thus reduces its oxidation number to +II, only to give it up again during the reaction with the next link and thus increase its oxidation number back to +III .

Location in the cell
Cytochromes are built into the inner membrane of mitochondria - the exception is cytochrome c, which is loosely bound to this membrane from the outside and which is also the only cytochrome that is soluble in water. The final element of electron transfer is the enzyme cytochrome oxidase (which contains copper as well as iron), which transfers electrons to inhaled oxygen and thus conditions the formation of water. (for a more detailed description of the reactions, see Electron transport chain )

Properties
Cytochromes are studied and classified mainly on the basis of radiation absorption. They have typical absorption spectra especially in the visible light region. (for more information on spectrophotometry, see Spectrophotometry )

Currently, the best-studied is cytochrome c. Scientists know that it is a protein with an extremely conservative sequence, in which more than a quarter of the amino acids of the chain have not changed through evolution even in 1.5 billion years. Not much information is known about other cytochromes.

Cytochrome-related diseases
A rare genetic disease known in English as cytochrome c oxidase deficiency affects, as the name suggests, cytochrome oxidase. There is not enough of it in the cells, the transfer of electrons and therefore the obtaining of energy for the organism is therefore not as effective as in other people. Tissues sensitive to lack of energy are particularly affected - skeletal muscles, myocardium, liver, nervous system. The severity of the disease is highly variable from patient to patient.

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Electron transport chain