Contrast the electron transport chain in photosynthesis with the one in cellular respiration by identifying sources of the high-energy electrons for each.

Respiration:

The respiratory chain detailed here is that of mammalian mitochondria:

NADH → NADH dehydrogenase → ubiquinone (coenzyme Q10) → coenzyme Q-cytochrome c reductase → cytochrome c → cytochrome c oxidase → O2;

succinate → succinate dehydrogenase → ubiquinone (coenzyme Q10) → coenzyme Q-cytochrome c reductase → cytochrome c → cytochrome c oxidase → O2.

It consists of the following elements:

The high transfer potential electrons of NADH are transmitted to coenzyme Q10 (ubiquinone) by NADH dehydrogenase, or complex I. Reduced coenzyme Q10 is ubiquinol Q10H2.

The electrons with a high succinate transfer potential are transferred to coenzyme Q10 by succinate dehydrogenase, or coenzyme II, also giving ubiquinol Q10H2.

Ubiquinol Q10H2 transfers its electrons to two cytochromes c under the action of coenzyme Q-cytochrome c reductase, or complex III.

Four cytochromes c each transfer their electron to an oxygen molecule under the action of cytochrome c oxidase, or complex IV. Two molecules of water are formed.

Each of these four respiratory complexes has an extremely complex structure partially included in the internal mitochondrial membrane. Apart from the complex II, they are proton pumps. The electrons circulate between these structures on liposoluble or hydrophilic electron transporters depending on the case.

Photosynthesis:

Photophosphorylation is the equivalent, for photosynthesis, of oxidative phosphorylation for cellular respiration. It constitutes the "light phase" of photosynthesis, that is, it groups together light-dependent reactions.

In plants, photophosphorylation occurs in the membrane of thylakoids, within chloroplasts:

H2O → photosystem II (P680) → plastoquinone → cytochrome b6f complex → plastocyanine → photosystem I (P700) → ferredoxin → ferredoxin-NADP + reductase → NADP +;

cyclic photophosphorylation: (ferredoxin →) plastoquinone → cytochrome b6f complex → plastocyanine → photosystem I (P700) → ferredoxin (→ plastoquinone).

Contrast:

What he has in common is:

*The sequence of several complex membrane proteins transporting electrons.

*The conversion of DNA into ATP.

The differences are in the transport proteins themselves, as well as the direction of H + flux (to the cytoplasm for photosynthesis, and to the mitochondrial matrix in respiration).

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