Respiration: Link reaction and Krebs cycle 12.2

What happens to the hydrogens lost by the pyruvate?

Accepted by NAD to form reduced NAD, which is later used to produced ATP.

How does pyruvate reach the matrix of the mitochondria from the cyptoplasm, where it is produced in glycolysis?

Actively transported.

Give four ways in which the Krebs cycle is important to respiration.

- Breaks down macromolecules into smaller ones e.g. pyruvate → CO₂ - Produces hydrogen atoms which are carried by NAD to electron transfer chains to provide energy for oxidative phosphorylation. - Regenerates 4-carbon molecule which bind with acetylcoenzyme A. - Source of intermediate compounds used by cells to produced other important substances such as fatty acids, amino acids and chlorophyll.

What products are produced from each molecule of pyruvate?

- Reduced coenzymes NAD and FAD. These have the potential to provide energy to produced ATP molecules by oxidative phosphorylation. - 1 molecule of ATP. - 3x molecules of CO₂.

Give the summary of the Krebs cycle.

1) 2-carbon acetylcoenzyme A combines with a 4-carbon molecule to produce a 6-carbon molecule. 2) 6-carbon molecule loses 2xCO₂ and hydrogen to form a 4-carbon molecule and 1 mole of ATP produced from substrate-level phosphorlyation. 3) NAD and FAD are reduced to form reduced NAD and reduced FAD. 4) 4-carbon moelcule can combine with a new molecule of acetylcoenzyme A.

What two changes occur in the link reaction?

1) Pyruvate is oxidised to acetate by losing a CO₂ molecule and two hydrogens. 2) 2-carbon acetate combines with coenzyme A to form acetylcoenzyme A.

What role do coenzymes play in respiration and photosynthesis?

Carry hydrogen atoms from one molecule to another.

Give another way of writing coenzyme A.

CoA.

What coenzyme is important in the Krebs cycle?

FAD.

Where does the link reaction and krebs cycle occur in eukaryotic cells?

In the mitochondria.

What are coenzymes?

Molecules that some enzymes require to function.

What coenzyme is important in respiration?

NAD.

What coenzyme is important in photosynthesis?

NADP.

What is the overall equation for the link reaction?

Pyruvate + NAD + CoA → acetyl CoA + reduced NAD + CO₂

What happens to the carbon dioxide?

Removed as a waste product during gaseous exchange.

What is the purpose of the link reaction?

To oxidise pyruvate.