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Learn Introductory Crop Physiology with Braimy – B.SC Agriculture
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During respiration simple carbohydrates and intermediate compounds like phosphoglyceraldehyde, pyruvic acid, isocitric acid, ά ketoglutaric acid, succinic acid and malic acid are oxidized. Each oxidative step involves release of a pair of hydrogen atoms which dissociates into two protons and two electrons.

2H 2H+ + 2eThese protons and electrons are accepted by various hydrogen acceptors like NAD,NADP, FAD etc. After accepting hydrogen atoms these acceptors get reduced to produce NADH2, NADPH2 and FADH2. The pairs of hydrogen atoms released a series of coenzymes and cytochromes which form electron transport system, before reacting with O2 to form H2O.

The composition of each of the respiratory chain complexes is shown below



No. of Proteins

Prosthetic Groups

Complex I

NADH Dehydrogenase


FMN, 9 Fe-S centers

Complex II

Succinate-CoQ Reductase


FAD, cyt b560, 3 Fe-S centers

Complex III

Complex IV

CoQ-cyt c Reductase

Cytochrome Oxidase



cyt bH, cyt bL, cyt c1, Fe-SRieske

cyt a, cyt a3, CuA, CuB

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