The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid cycle, is a series of chemical reactions that occurs within the mitochondria of cells to break down pyruvic acid from glycolysis into carbon dioxide. It was discovered by Hans Adolf Krebs in the 1930s and completes the oxidation of organic molecules. The cycle involves 8 steps where pyruvic acid is converted into acetyl CoA which enters the Krebs cycle. As compounds go through decarboxylation and oxidation reactions, electrons are transferred to create ATP, NADH, FADH2, and CO2.

1. Thanh Uyen Pham
Snousha Glaude
Chelsea Farber
Ap Biology

2. 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 mitochrondrion
Requires energy (aerobic phase)
Two pyruvate were broken down
from one glucose during glycolysis,
thus the Krebs cycle will occur twice
for every glucose.

3. 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)

4. 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.

5. 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

6. 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

7. 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.

8. 7th
: Water is added to fumarate to form malate
8th
: The malate is
oxidized to form
the 4-carbon
oxaloacetate
--the step formed another NADH

9.  Animation from McGraw-Hill

10. 1 ATP
3 NADH
1 FADH2
2 CO2

11. THE END