Gregorich SBI4U - The Kreb's Cycle

The Kreb's Cycle was discovered by Hans Krebs in 1937. It is the third series of steps in Cellular Respiration that occurs exclusively in the Matrix of the mitonchondria. It consists of 8 enzyme catalyzed reactions, beginning with the 2-Carbon Acetyl-CoA (the final product of Pyruvate Oxidation) combining with a 4-Carbon oxaloacetate to form 6-Carbon Citrate (it is also known as: The Citric Acid Cycle).

As the molecules pass through "the cycle", the Citrate is Decarboxylated (stripped of CO₂) and Dehydrogenated (stripped of Hydrogen and it's high energy electrons!). These 2 CO₂ molecules are removed as waste, while the Hydrogens and electrons are picked up by NAD+ and FAD (forming NADH and FADH₂ respectively). One ATP is produced indirectly through the formation and breaking down of GTP. By the end of the cycle, oxaloacetate is regenerated to begin the process again.

Overall, 1 ATP, 3 NADH and 1 FADH₂ are produced through one "turn" of the cycle. Keep in mind that one glucose molecule produces 2 pyruvates, so one glucose molecule will go through 2 "turns", producing 2 ATP, 6 NADH and 2 FADH₂per molecule of glucose.

Textbook Practice

Read p.174-177