Question

SECTION 34 Electron Transport PRE-ACTIVITY ASSIGNMENT 1. Produce a reading outline for the section in your textbook that covers electron transport. 2. Under standard conditions, will the following reactions proceed spontaneously as written? a. 2 Cytochrome c (Fe3+) + NADH = 2 Cytochrome c (Fe2+) + NAD+ b. Cyto a (Fe2+) + cyto b (Fe3+) = Cyto a (Fe3+) + cyto b (Fe2+)

Answer 1

Let us learn first something about the chemistry and structure of cytochrome C here.

Having learned something on cytochrome C, we need to understand that it is a transport protein and the active centre Iron present in it facilitates this transport via its reduction and oxidation.

SOUS CH! Clic!, wat cytochrome c. H acts as an e carne → It operates by s postein shuttling between / Felll) & Fe (ll) at their active state The Home group in cytic has a poly- it's Replice chain attached & 'wrapped celolind it. - CH₂ CH₂ Crot - chain contains a lanable no: of amino auds, (103 -112) : » A'll atom from histidine segment . s. Met and sulphur atom from methionine segment of this chain is coordinated to the 5th and 6th Co-ordinahon silīs of fe atom. L → As all the coordination files are filled it cannot coordinate with the op. as in the case of tlamoglobin. filled of team

In the electron transport chain ATP molecules are synthesised by undergoing oxidative phosphorylation.

a. In simple words in the electron transport chain the electrons released when NADH is oxidised is in a higher energy state and they are transported from this higher energy state to a lower energy states with each step till it reaches the ATP synthase and eventually form ATP from ADP and the electrons.

So there are a lot of high energy electron carriers present and Cytochrome is one of them.

The reaction of NADH + Cytochrome fe3+ giving cytochrome fe2+ and NAD+ doesnt takes place as easily as it is written . It takes place because of other high energy electron carriers present in them and also due to the potential gradient developed in the inner mitochondrial matrix.

The reduction potential of the cytochrome oxidase reaction is +0.82 V. Beginning with the initial electron donor, cytochrome c, and ending with the final electron acceptor, O2, we see that the reduction potential goes from +0.27 V to +0.82 V. This increase in reduction potential from the electron donor to the electron acceptor makes the overall reactions of cytochrome oxidase spontaneous.

b . Still as these areas are under study we cannot quite confidently say about the thermodynamics of the reaction. But we can say in the most simple way that the cytochromes are electron transport protein and the electrons are transferred from one to another.

So the electrons carried by cytochrome a is released as they undergo oxidation and these electrons are taken by the cytochrome b by undergoing reduction . It is easy and as simple as that but for the each of the reaction to take place in a biological system certain concentration gradient must be present for the protons of the innermitochrondrial matrix and the intermembrane of mitochondria.