citric acid cycle

The Tricarboxylic Acid Cycle(The Citric Acid Cycle)
Babylon university
College of pharmacy
Department of clinical and scientific laboratory
3rd class – biochemistry
Second semester
Dr. Abdulhussien M. K. Aljebory

Krebs in mitochondrial matrix
Mitochondrion
Outer membrane very permeable
Space between membranes called intermembrane space
Inner membrane (cristae)
Permeable to pyruvate,
Impermeable to fatty acids, NAD, etc
Matrix is inside inner membrane

Aerobic cells use a metabolic wheel – the citric acid cycle – to generate energy by acetyl CoA oxidation
A series of consecutive biochemical reactions catalyzed by enzymes that produce a specific end product.
Catabolism- the breakdown of food stuffs to simple organic chemicals.
Anabolism- the synthesis of biomolecules from simple organic chemicals.

Three main pathways for energy production:1- Glycolysis 2- Citric acid cycle3- Oxidative-Phosphorylation

Certain pathways are involved in both breakdown and buildup of molecules these pathways are called amphibolic. The citric acid cycle is an example of this.
Eight successive reaction steps.
The six carbon citrate is formed from two carbon acetyl-CoA and four carbon oxaloacetate.
Oxidation of citrate yields CO2 and regenerates oxaloacetate.
The energy released is captured in the reduced coenzymes NADH and FADH2.

A four-carbon oxaloacetate condenses with a two-carbon
acetyl unit to yield a six-carbon citrate.
An isomer of citrate is oxidatively decarboxylated and
five-carbon ?-ketoglutarate is formed.
?-ketoglutarate is oxidatively decarboxylated to yield a
four-carbon succinate.
Oxaloacetate is then regenerated from
succinate.
Two carbon atoms (acetyl CoA) enter the
cycle and two carbon atoms leave the cycle in
the form of two molecules of carbon dioxide.
Three hydride ions (six electrons) are
transferred to three molecules of NAD+, one
pair of hydrogen atoms (two electrons) is
transferred to one molecule of FAD.