Thanh Uyen PhamSnousha GlaudeChelsea Farber

Ap Biology

Other names: Citric acid cycle & tricarboxylic acid cycle

Discovered by Hans Adolf Krebs in the 1930s.Krebs Cycle completes the oxidation of organic molecules (to breakdown the pyruvic acid

to CO2). Occurs within the mitochrondrionRequires energy (aerobic phase)Two pyruvate were broken down

from one glucose during glycolysis, thus the Krebs cycle will occur twice for every glucose.

Oxidation: the process of losing electrons from a chemical element or compound

Decarboxylation: the process of removing a carboxyl group (CO2) from a chemical compound (usually replacing it with hydrogen)

Before the cycle begins, pyruvic acid obtained from glycolysis is converted into an acetyl Coenzyme A (acetyl CoA)

This occurrence produced a CO2 and formed an NADH molecule.

1st: Acetyl CoA enters the mitochrondria, its 2-carbon acetyl is transferred to a 4-carbon compound oxaloacetate, releasing the CoA carrier.

This process produced a 6-carbon compound citrate

2nd: The citrate is rearranged to form its isomeric form, isocitrate, by the removal of an H2O and addition of an H2O

3rd: The compound decarboxylated a CO2, becoming oxidized to form a 5-carbon compound alpha-ketoglutarate

The step decarboxylated the carboxyl group (CO2) and hydrogen is remove and transfer to NAD+ to formed NADH

4th: The compound is decarboxylated and oxidized, forming a 4-carbon compound succinyl-CoA (with the attachment of a CoA carrier)

This step resulted in the release of a CO2 and formation an NADH

5th: CoA carrier is release by a phosphate group, turning the compound from succinyl-CoA to succinate

--The phosphate is transferred to

GDP to make GTP, which is converted to ADP and then finally to ATP

6th: 2 Hydrogen are released, transferred to FAD, forming FADH2, the 4-carbon succinate is oxidized to form a fumarate.

7th: Water is added to fumarate to form malate8th: The malate isoxidized to form the 4-carbon oxaloacetate--the step formed another NADH

Animation from McGraw-Hill

1 ATP 3 NADH 1 FADH2

2 CO2

THE END