The Tricarboxylic Acid Cycle (TCA)

TCA

The Tricarboxylic Acid Cycle

OAA

oxaloacetic acid

The kreb cycle reaction is catalysed by the enzyme

citrate synthase

The Tricarboxylic Acid Cycle (TCA)

• also known as the Citric Acid Cycle or Krebs Cycle, is a series of chemical reactions used by all aerobic organisms to generate energy

Acetyl Group and Oxaloacetic Acid (OAA)

The TCA ( The Tricarboxylic Acid Cycle )cycle starts with the condensation of an acetyl group with OAA Oxaloacetic Acid and water to yield citric acid. This reaction is catalysed by the enzyme citrate synthase and a molecule of CoA is released.

Decarboxylation

This is followed by two successive steps of decarboxylation, leading to the formation of

α-ketoglutaric acid and then succinyl-CoA.

Succinyl-CoA to OAA

• In the remaining steps of the citric acid cycle, succinyl-CoA is oxidised to OAA, allowing the cycle to continue.

• During the conversion of succinyl-CoA to succinic acid, a molecule of GTP is synthesised.

• This is a substrate-level phosphorylation.

GTP to GDP

In a coupled reaction, GTP is converted to GDP with the simultaneous synthesis of ATP from ADP.

Reduction of NAD+ and FAD+

• There are three points in the cycle where NAD+ is reduced to NADH

• + H+ and

• one point where FAD+ is reduced to FADH2.