The Citric Acid Cycle Flashcards
What is the purpose of the citric acid cycle?
Electrons are required for ATP to pass down the electron transport chain.
These electrons come from electron carriers such as NADH and FADH₂, which are produced by the Citric Acid Cycle.
What are the other names of the citric acid cycle?
Tricarboxylic acid cycle (TCA cycle)
Kreb’s cycle
What reaction occurs prior to the citric acid cycle?
Glycolysis - generates pyruvate, ATP and NADH.
Pyruvate is decarboxylated to acetyl-CoA by the pyruvate decarboxylase complex.
Acetyl-CoA is the intermediate that enters the TCA cycle.
Define decarboxylated
Eliminate a carboxyl acid group
What is the role of the citric acid cycle?
Production of NADH and FADH2
Step One
Acetyl CoA (two carbon molecule) joins with oxaloacetate (4 carbon molecule) to form citrate (6 carbon molecule).
Step Two
Citrate is converted to isocitrate (an isomer of citrate)
Step Three
Isocitrate is oxidised to alpha-ketoglutarate (a five carbon molecule) which results in the release of carbon dioxide. One NADH molecule is formed.
What enzyme is involved in catalysing step three?
Isocitrate dehydrogenase
This is a rate limiting step, as isocitrate dehydrogenase is an allosterically controlled enzyme.
Step Four
Alpha-ketoglutarate is oxidised to form a 4-carbon molecule.
This binds to coenzyme A, forming succinyl CoA.
The second molecule of NADH is produced, alongside a second molecule of carbon dioxide.
Step Five
Succinyl CoA is then converted to succinate (4 carbon molecule) and one GTP molecule is produced.
Step Six
Succinate is converted into fumarate (4 carbon molecule) and a molecule of FADH₂ is produced.
Step Seven
Fumarate is converted to malate (another 4 carbon molecule).
Step Eight
Malate is then converted into oxaloacetate. The third molecule of NADH is also produced.
What is the net output of each cycle?
Two molecules of carbon dioxide.
Three molecules of NADH.
Three hydrogen ions (H+).
One molecule of FADH₂
One molecule of GTP.
