Question

Which of the following is true regarding the given electron transport chain?
CoQ→ Cyt c→ Cyt $a{a_3}$ →${O_2}$ ​
A. CoQ→ Cyt c is ${H^ + }$ absorbing site
B. $a{a_3}$ ​→${O_2}$ ​, ${H^ + }$ yielding site
C. CoQ→ Cyt c is ${H^ + }$ yielding site and $a{a_2}$ ​→${O_2}$ is ${H^ + }$ absorbing site
D. No ${H^ + }$ is absorbed or released

Answer 1

Hint: The electron transport chain (ETC) is a series of events which transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation) reactions, and couples this electron transfer with the transfer of protons (${H^ + }$ ions) across a membrane.

Complete step by step answer:
The electron transport chain is made up of peptides, enzymes, and other molecules. Most eukaryotic cells have an organelle known as mitochondria, which produces ATP from the products of the citric acid cycle, fatty acid oxidation, and amino acid oxidation. At the inner mitochondrial membrane, electrons from NADH and $FAD{H_2}$ pass through the electron transport chain to oxygen, which is reduced to water .this Passage of electrons between donor and acceptor releases energy, which is used to generate a proton gradient across the mitochondrial membrane by "pumping" the protons into the intermembrane space, and producing a thermodynamic state that has a great potential to do work. This entire process is known as oxidative phosphorylation since ADP is phosphorylated to ATP by using the electrochemical gradient established by the redox reactions of the electron transport chain.
${H^ + }$ of $NAD{H^ + }$ (received from Krebs cycle) is accepted by FAD as a result of which FAD is reduced to $FAD{H^ + }$ and $NAD{H^ + }$ is oxidised to NAD. Reduced FADH is oxidised by CoQ, with the formation of $CoQ{H^ + }$ .
${H^ + }$ ions then move to the Cyt b, then Cyt c,then Cyt a and then Cyt $a{a_3}$ . Ultimately these ${H^ + }$ are accepted by ${O_2}$ and ${H_2}O$ is formed.

So the correct answer is option C.

Note: Reverse electron flow, is the transfer of electrons from the electron transport chain through the reverse redox reactions. It requires a significant amount of energy to be used, this can result in reducing the oxidised form of electron donors.