introduction , cycle and steps

1. CITRIC ACID CYCLE
FACULTY MOHD
ADIL

2. The citric acid cycle (Krebs cycle or tricarboxylic acid-TCA cycle occurs In
Mitochondria and in Aerobic conditions) is the most important metabolic
pathway for the energy supply to the body. Citric acid cycle essentially
involves the oxidation of acetyl CoA to CO2 And H2O.
Krebs cycle basically involves the combination of a two-carbon acetyl
CoA with a four-carbon oxaloacetate to produce a six-carbon
tricarboxylic acid(citrate).

4. Reactions of citric acid cycle
1.Formation of citrate: Krebs cycle proper starts with the condensation of acetyl CoA and oxaloacetate (play a
catalytic role in citric acid cycle) catalysed by the enzyme citrate synthase.
2and 3. Citrate is isomerized to isocitrate by the enzyme aconitase. This is achieved in a two-stage reaction of
dehydration followed by hydration through the formation of an intermediate -cis-aconitate.
4. and 5. Formation of a-ketoglutarate: The enzyme isocitrate dehydrogenase (lCD) catalyses the conversion
(oxidative decarboxylation) of isocitrate to oxalosuccinate and then to α-ketoglutarate. The formation of NADH
and the liberation of CO2 occur at this stage.
6. Conversion of α-ketoglutarate to succinyl CoA occurs through oxidative decarboxylation, catalysed by α-
ketoglutarate dehydrogenase complex. This enzyme is dependent on five cofactors-TPP, lipoamide, NAD+, FAD
and CoA. At this stage of the TCA cycle, second NADH is produced and the second CO2 is liberated.