Saturday, March 19, 2011

Cellular Respiration: Oxidative Phosphorylation

The below diagram is a good summary of what happens during oxidative phosphorylation (including the electron transport chain and ATP synthesis)
During this process, electrons are passed to a series of enzymes via electron carriers.
It is first given to NADH dehydrogenase, then carried to the cytochrome b-c complex by ubiquinone, then carried to the cytochrome oxidase complex by cytochrome c. Here, oxygen acts as the final electron acceptor. These enzymes are in order of increasing electron affinity.
For every electron passed at each of the enzymes, energy obtained is used to transport a H+ ion into the inner membrane space of the mitochondria.
This creates potential energy in the form of positive charge build up.
Finally, these protons enter the matrix through the ATP synthase structure creating one ATP molecule for every H+ that was pumped out.

Why is the net ATP production of cellular respiration 36-38?
This is because, as can be seen from the overall diagram of cellular respiration on the right, the NADHs that are produced during glycolysis must be brought into the matrix of the mitochondria. Passage through the outer membrane is simple, however, they cannot pass through the inner membrane without some help.
There are 2 ways this occurs: through aspartate or glycerate phosphate.
When aspartate is used, the NADH passes through as NADH.
When glycerate phosphate is used, the electron passes through and attaches to FAD to make FADH2.

NADH enters at first enzyme of ETC pumping 3 electrons, creating 3 ATPS.
NADH enters at second enzyme of ETC pumping 2 electrons, creating 2 ATPS.

This is why there may be slight variations.

Reactants: 6NADH (from Krebs), 2NADH (from pyruvate oxidation), 2FADH2 (from Krebs), 2FADH2 OR 2NADH (from Glycolysis), 32-34 ADP, 32-34 phosphate groups, 6Oxygen molecules, 12H+
Products: 8-10NAD+, 2-4FAD+, 24H+, 32-34 ATP, 6Water molecules
Location: Inner membrane of the mitochondria
Net ATP: 32-34

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