Question

Describe the oxidation-reduction that the components of the electron transport chain undergo as electrons are accepted and donated. Include in your answer the direction of electronegativity as well as the separate roles of the components of the electron transport chain including flavin mononucleotide, the Fe-S group, ubiquinone, and the cytochromes.

Answer 1

Electron transport chain is a process in which electron is transferred between various electron Carriers. It takes place in thylakoid membrane in chloroplast and in inner mitochondrial membrane. It is a part of both photosynthesis and cellular respiration.

Electron Carriers are arranged according to their electronegativity or redox potential. The electron carrier with lower redox potential is present initially and then the potential of Carriers increases. The one with lower redox potential has lower affinity for electrons and the one with higher redox potential has higher affinity for electrons.

When electrons are transported from one electron carrier to the other the previous carrier is oxidized and the carrier which gives electron gets reduced. Along with the transportation of electrons, each electron carrier also transports hydrogen ion from mitochondrial Matrix to intermembrane space in mitochondria and thylakoid lumen to stroma in chloroplast. This creates a differential gradient of protons across the inner mitochondrial membrane and thylakoid membrane. The protons are then pumped back into the mitochondrial matrix and thylakoid lumen by ATP synthase enzyme. This causes spinning of the enzyme and therefore results in synthesis of ATP from ADP and inorganic phosphate.

The electron transport chain occurs between 4 complexes in mitochondria.

The electron donors are high energy electron carriers, NADH and FADH2, which were generated in glycolysis, pyruvate oxidation and citric acid cycle.

The electron is then accepted by the first Complex of electron transport chain called as NADH reductase. NADH is oxidized to NAD+ by reducing flavin mononucleotide to FMNH2. The electrons are then transferred to to iron-sulfur cluster of ubiquinone (coenzyme Q).

The mobile electron coenzyme Q which also receive electrons from complex two or succinate dehydrogenase. Coenzyme Q also called as ubiquinone, passes electrons to 3rd complex, cytochrome bc1 complex. This Complex passes them to cytochrome C which is also a mobile electron carrier and ultimately the electrons are accepted by oxygen to form water which is the byproduct of cellular respiration.

This is how electron transport chain in mitochondria works.

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