4. The Krebs Cycle

Where does the Krebs Cycle occur?

Mitochondria

What does the Krebs cycle produce?

reduced coenzymes:

ATP

Explain the process:

1. Formation of a 6-carbon compound

   • Acetyl CoA from the link reaction combines with a four-carbon molecule (oxaloacetate) to firm a six-carbon molecule (citrate).

2. Formation of a 5-carbon compound.

   • Citrate molecule is converted to a five-carbon molecule by decarboxylation with the removal of carbon dioxide.'

   • Dehydrogenation also occurs. The hydrogen is used to produce NAD from NAD.

3. Regeneration of oxaloacetate

   • The five-carbon molecule is then converted to a four-carbon molecule.

   • Decarboxylation and Dehydrogenation occur.

   • This produces one molecule of reduced FAD and 2 of reduced NAD. ATP is produced by a direct transfer of a phosphate group from an intermediate compound to ADP (substrate-level phosphorylation).

   • Citrate has now been converted into oxaloacetate.

Substrate-level phosphorylation

When a phosphate group is directly transferred from one molecule to another.

Draw the Krebs Cycle.

products of the Krebs Cycle:6

Where does each go?

• 1 coenzyme A - Re-used in the next link reaction

• Oxaloacetate - Regenerated for use in the next Krebs cycle.

• 2 carbon dioxide - Released as a waste product.

• 1 ATP - Used for energy

• 3 Reduced NAD - Oxidative phosphorylation

• 1 reduced FAD - Oxidative phosphorylation.