Link Reaction and Kreb's Cycle

Significance of Krebs cycle
1. Breaks down macromolecules into smaller one; pyruvate is broken down into carbon dioxide
2. Produces hydrogen atoms that are carried by NAD to the electron transport chain for oxidative phosphorylation
  1. Produces ATP that provides metabolic energy for the cell
3. Regenerates the 4-carbon molecule that combines with acetylcoenzyme A, which would otherwise accumulate
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
Coenzymes
1. NAD
  1. Hydrogen carrier - important for respiration
2. FAD
  1. Important in Krebs cycle
3. NADP
  1. Important in photosynthesis
Link Reaction
1. Pyruvate is oxidised by removing hydrogen
  1. The hydrogen is accepted by NAD to form reduced NAD which is later used to produce ATP
2. The 2-carbon molecule (acetyl group) that is formed combines with coenzyme A (CoA) to produce acetylcoenzyme A
3. A carbon molecule is formed from each pyruvate
4. Pyruvate + NAD + CoA --> acetyl CoA + reduced NAD + CO2
Krebs Cycle
1. Occurs in the matrix of the mitochondria
2. 2-carbon acetylcoenzyme A from the link reaction combines with a 4-carbon molecule
  1. Produces a 6-carbon molecule
3. The 6-carbon molecule loses carbon dioxide and hydrogens
  1. Gives a 4-carbon molecule and a single molecule of ATP as a result of substrate-level phosphorylation
4. The 4-carbon molecule can now combine with a new molecule of coenzyme A
  1. Begins the cycle again
For each molecule of pyruvate, the link reaction and Krebs cycle therefore produce:
1. 1 molecule of ATP
2. 3 molecules of carbon dioxide
3. reduced coenzymes such as NAD and FAD
  1. These have the potential to produce ATP molecules and therefore the important products of Krebs cycle

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Link Reaction and Kreb's Cycle

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	Created by laura.dyer86 over 11 years ago