The Krebs Cycle Flashcards
(12 cards)
Describe the steps of the Krebs cycle
- Acetyl-CoA combines with Oxaloacetate to produce Citrate. Enzyme= citrate synthase
- Citrate undergoes isomerisation using enzyme Aconitase to produce Isocitrate.
- Isocitrate undergoes oxidation to become alpha-ketoglutarate. Enzyme= Isocitrate dehydrogenase. Produces NADH.
- Alpha-ketoglutarate into Succinyl-CoA using enzyme alpha-ketoglutarate dehydrogenase. Produces NADH.
- Succinyl-CoA converted into Succinate using enzyme Succinyl-CoA synthetase. Produces ATP.
- Succinate into Fumarate using enzyme Succinate dehydrogenase. FADH2 produced.
- Fumarate into Malate using enzyme Fumarase.
- Malate to Oxaloacetate using enzyme Malate dehydrogenase. NADH produced. Positive Gibbs free energy value.
What is the role of the link reaction ?
It converts pyruvate (end product of glycolysis) into Acetyl-CoA which is the molecule that enters the Krebs cycle
Describe the steps of the link reaction
- Pyruvate combines with TPP. Pyruvate looses one carbon as CO2.
- The hydroxyethyl groups is oxidised to an Acetyl group then transferred to the lipoamide, forming Acetyl-lipoamide.
- The Acetyl group is transferred to Coenzyme A. Acetyl-CoA is formed and released. Liopamide is now in its reduced form- dihydrolipoamide.
- E3 then oxidises the reduced form back into lipoamide. Electrons are transferred to FAD then to NAD+.
What is pyruvate dehydrogenase complex ?
It is a multi-enzyme complex composed of 3 core enzymes and requires 5 cofactors.
It is used in the link reaction.
Enzymes:
1. Pyruvate dehydrogenase (E1)
2. Dihydrolipoyl transferase (E2)
3. Dihydrolipoyl dehydrogenase (E3)
Cofactors:
1. TPP
2. Lipoic acid
3. Coenzyme A
4. NAD+
5. FAD
What is Beriberi ?
Vitamin B1 deficiency- Thiamine
Neurological and cardiovascular symptoms
Raised blood pyruvate levels
What enzyme does mercury inhibit ?
Pyruvate dehydrogenase
Coenzyme for riboflavin-B2
FAD
Coenzyme for Niacin
NAD+
Coenzyme for B12
5’-Deoxyadenosyl cobalmine
Coenzyme for Pantothenic acid
CoA
Coenzyme for Pantothenic acid
CoA
Where do the Krebs cycle and link reaction occur ?
Mitochondrial matrix
