Link Reaction and Krebs Cycle

Link Reaction and Krebs Cycle

Where ?

Both reactions take place in the matrix of the mitochondria.

The Process

·         Pyruvate is oxidised by NAD which removes a hydrogen to from reduced NAD (this is later used to produce ATP in the electron transport chain).

·         A 2-carbon acetyl group combines with a molecule known as co-enzyme A to from Acetyl co-enzyme A.

·         A carbon dioxide molecule is formed from each pyruvate

The basic word equation is :

Pyruvate + NAD + CoA --> Acetyl CoA + reduced NAD + Carbon Dioxide

Note CoA stands for Co-enzyme A

The Krebs Cycle

The Krebs cycle is a series of oxidation reduction reactions that take place inside the matrix of the mitochondrion.

1.      The 2-Carbon Acetyl- coenzyme A from the Link reaction combines with a 4 carbon molecule to produce a 6 carbon molecule.

2.      This 6 carbon molecule loses two carbon dioxides and hydrogen's to from a 4 carbon molecule. A single ATP molecule is produced as a result of substrate level Phosphorylation

3.      The 4 carbon molecule can now re combine with Acetyl-coenzyme A to start the cycle again (by producing the 6 carbon molecule again)

For 1 pyruvate molecule the link reaction and kerbs cycle produce

·         3 molecules of carbon dioxide

·         One molecule of ATP

·         Reduced NAD

·         Reduced FAD

Note that these molecules are given off when the 6-carbon molecule is broken down to the 4 carbon molecule.

Coenzymes

In respiration and photosynthesis, hydrogen atoms are carried by coenzymes from one molecules to another. They include :

1.      NAD

2.      FAD- Krebs cycle

3.      NADP - Photosynthesis

Significance of the Krebs Cycle

The Krebs Cycle is important for 4 reasons

1.      It breaks macromolecules down into smaller ones. For example Pyruvate is broken down to carbon dioxide.

2.      It regenerates the 4- carbon molecule that combines with acetyl-coenzyme A.

3.      It produces Hydrogen atoms that are carried by NAD to the electron transport chain.

4.      It is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll.