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Where does the citric acid cycle occur?
mitochondrion
What are the three main phases of the citric acid cycle?
- The production of isocitrate - a 6C molecule
- Two decarboxylations 6C -> 5C -> 4C
- The regeneration of oxaloacetate
What is the first molecule in the citric acid cycle?
Acetyl CoA
What is the final molecule produced in the CAC?
Oxaloacetate which is also part of the first step
What happens in the first step of the CAC?
- A 2 carbon molecule (acetyl CoA) and a 4 carbon molecule (Oxaloacetate) are combined to make a 6 carbon molecule (citrate). This is a condensation reaction
- citrate is converted to its isomer isocitrate. This is isomerization.
What happens after the first step of the citric acid cycle?
Citrate undergoes changes to go from a 6 carbon molecule down to a 4 carbon molecule (oxaloacetate), releasing 2 CO2.
Where does Acetyl CoA come from?
pyruvate oxidation
What happens in the second phase of the citric acid cycle?
- isocitrate is oxidized by isocitrate dehydrogenase, leaving behind a 5 carbon molecule (ketoglutarate) and releasing CO2. NAD+ is reduced to NADH
- Ketoglutarate is oxidized, reducing NAD+ to NADH and releasing a CO2. This 4 carbon molecule picks up succincyl CoA. The enzyme is ketoglutarate dehydrogenase
What happens in phase 3?
- Succinyl CoA is used to carry out substrate level phosphorylation of GDP -> GTP. Remaining 4 carbon molecule is succinate. Enzyme is succinyl CoA synthetase.
- Succinate is oxidized to form fumarate. FAD is reduced to FADH2
- Water is added to the four carbon molecule fumarate, converting it to malate
- Malate is oxidized, returning the 4 carbon molecule to oxaloacetate. NAD+ is reduced to NADH.
What are the overall reactants of citric acid cycle?
Acetyl CoA, 3 NAD+, FAD, GDP, and P+
What are the overall products of citric acid cycle
2 CO2, 3 NADH, 3 H+, FADH2, GTP, CoA
Where does the citric acid cycle occur in prokaryotic cells?
cytoplasm
How many electron pairs on Acetyl CoA and what do they do?
Four electron pairs reduce NAD+ (3) and FAD (1)
What are the rate limiting enzymes of citric acid cycle?
citrate synthase and isocitrate dehydrogenase
Major regulators of citric acid cycle are
substrate (acetyl coa and oxaloacetate) and product (NADH)
What is the key regulator of the citric acid cycle?
NADH/NAD+ ratio. If NADH gets high, cycle slows because it's linked to ATP and energy of the cell.
What is the energy yield from the complete oxidation of glucose?
38 ATP
