Question

What is a complex IV in the ETS of mitochondria?

Answer 1

The electron transport chain (ETC; respiratory chain) is a collection of protein complexes that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occur at the same time) and couple this electron transfer with proton ($H^+$ ion) transfer across a membrane. Peptides, enzymes, and other compounds make up the electron transport chain.

Complete answer:
The electron transport chain's Complex IV, commonly known as cytochrome c oxidase, is a multi-unit structure that transfers electrons from cytochrome c to oxygen, forming water in the process and assisting in the generation of a proton gradient. Two heme groups, heme A and heme A-3, as well as three copper ions, make up cytochrome c oxidase. CuA/CuA is the centre formed by two copper ions, and CuB is the third copper atom. CuB forms a complex with heme A-3 to aid in the reduction of oxygen in the water. A total of four reduced cytochrome c molecules will bind to complex IV in a sequential fashion, each emitting a single electron.

The initial electron will be transferred to the CuA/CuA centre, followed by heme A, heme A-3, and then CuB. The CuB will be reduced from a +2 state to a +1 state as a result of this. The second electron travels to heme A-3 and decreases it. These two groups will bind an oxygen molecule from the peroxide bridge between heme A-3 and CuB when they are totally reduced. Each of the groups will take two more electrons, and the peroxide bridge will be broken between the CuB-OH and Heme A3-OH groups when two protons (from the matrix) are bound.

In the process of electron movement, a total of four protons will be pumped out of the matrix and into the intermembrane space by complex IV. The oxidation of A-3 groups will return them to their former condition. Complex IV will pump four protons out of the matrix and into the intermembrane gap during the electron transport phase.

Cytochrome c oxidase is another name for Complex IV. It has two copper centres, two heme, and two cytochromes a and a3. The name cytochrome c oxidase comes from the fact that Complex IV absorbs electrons from cytochrome c. Electrons are transferred to O2 by Complex IV. By absorbing two hydrogen ions, oxygen functions as a final electron acceptor and converts to water.

An enzymatic succession of electron donors and acceptors make up the electron transport chain. Each electron donor will pass electrons to a more electronegative acceptor, which will then donate them to another acceptor, and so on until electrons reach oxygen, the most electronegative and terminal electron acceptor in the chain.

The transfer of electrons between donor and acceptor releases energy, which is used to create a proton gradient across the mitochondrial membrane by 'pumping" protons into the intermembrane space, resulting in a thermodynamic condition capable of doing work. Because ADP is converted to ATP using the electrochemical gradient generated by the electron transport chain's redox processes, this complete process is known as oxidative phosphorylation.

Note: ATP synthase is the electron transport chain's complex V. The F O subunit of ATP synthase functions as an ion channel, allowing protons to flow back into the mitochondrial matrix. The free energy produced during the formation of the oxidised versions of the electron carriers (NAD + and Q) is released during this reflux. Free energy is needed to fuel ATP production, which is catalysed by the complex's F 1 component.