In the breakdown of glucose and other sugars, most of the ATP is formed
by a cyclical series of reactions called the citric acid cycle
or Krebs cycle. CO2 is formed in this cycle.
Most of the ATP is made indirectly via NADH+ and the electron
transport chain.
Production of Acetyl Coenzyme A:
Pyruvate + Coenzyme A + NAD+
——> Acetyl Co-A + CO2
+ NADH + H+
Acetyl coenzyme A also results from the breakdown of fats and proteins.
Krebs cycle reactions:
[Click here to show the reactions]
- These reactions are sometimes written
in terms of oxaloacetic acid, citric acid, etc., but in living
cells these compounds are usually ionized as citrate, oxaloacetate, etc.
- Many of these reactions are reversible, and are also used in amino
acid synthesis.
- In eucaryotes, Krebs cycle reactions take place inside mitochondria,
with some of the enzymes bound to cristae of the inner membrane while
others float freely in the fluid matrix.
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