What is oxidative phosphorylation?

Oxidative phosphorylation is the metabolic pathway in which the mitochondria in cells use the energy released by the oxidation of nutrients to synthesize ATP.

Here is a highly condensed summary of the process.

Stage 1 is glycolysis.

Glycolysis is a 10-step pathway. The overall reaction is

#"C"_6"H"_12"O"_6 + "2NAD"^+ + "2ADP" + "2P" → 2underbrace("CH"_3"(C=O)COOH")_color(red)("pyruvate") + "2ATP" + "2NADH" + "2H"^+#.

Stage 2 is oxidative decarboxylation.

The overall equation is

#"pyruvate" + "CoA" + "NAD"^+ → "acetyl-CoA" + "NADH" + "H"^+ + "CO"_2#

The essential feature is that #"NAD"^+# is used to remove two H atoms and 2 electrons from pyruvate.

The NADH then heads off to the electron transport chain to help create more ATP, and the acetyl-CoA enters the Tricarboxylic Acid Cycle.

Stage 3 is the Tricarboxylic Acid Cycle

The Tricarboxylic Acid Cycle is a series of eight reactions that occur in the inner layer of the mitochondrion.

They completely oxidize acetate to carbon dioxide.

The overall equation is:

#"2acetyl-CoA" + "6NAD" + "2FAD" + "2ADP" + "2P" +"4H"_2"O" → "4CO"_2 + "2CoA" + "6NADH"^+ + "FADH"_2+ + "2ATP" + "6H"^+#

The energy is produced is stored in #"ATP"#, #"NADH"#, and #"FADH"_2#.

The #"NADH"# and #"FADH"_2# proceed to the electron transport chain.

Stage 4 is the Electron Transport Chain

Here the #"H"^+# ions and electrons produced in the previous steps combine with oxygen to form water.

As the hydrogen ions flow, ATP is made from ADP and phosphate ions.

The net reaction is:

#"2ADP" + "2P" + "2NADH" + "O"_2 + "2H"^+ →"2ATP" + "2NAD"^+ + "2H"_2"O"#

In total, one glucose molecule yields about 32 ATP molecules by oxidative phosphorylation.

Oxidative phosphorylation accounts for around 90 % of the body's total ATP.