Cell metabolism II Flashcards
What is the role of the Krebs/ TCA cycle?
Converts the acetate group to carbon dioxide and hydrogen.
Produces reduced co-factors which generate ATP when re-oxidised in the ETC
How does acetyl CoA enter the TCA cycle?
CoA transfers the acetate group (2C) to oxaloacetate (4C) to form citrate (6C)
Where does the TCA cycle occur?
Mitochondrial matrix
What are the steps of the TCA cycle
Citrate –> isocitrate –> alpha-ketoglutarate –> succinyl CoA –> succinate –> fumarate –> malate –> oxaloacetate
What are the products of the TCA cycle
1 FADH2, 1 GTP, 1ATP, 2 CO2, 3 NADH
How many molecules of water required for one turn?
2
How can amino acids enter the TCA cycle?
Glucogenic AA have their amino group removed so that their carbon skeleton can enter the TCA cycle
Ketogenic AAs form ketone bodies once their amino group is (either acetyl CoA or acetoacetyl CoA), which can also enter the TCA cycle
Occurs via transamination reactions
What are transamination reactions?
Process by which amino acids are removed and transferred to acceptor keto acids
What molecules arise from transamination of amino acids?
Acetyl CoA
Acetoacetyl CoA
Pyruvate
Alpha-ketoglutarate
Succinyl CoA
Fumarate
Oxaloacetate
How does alanine undergo transamination?
Alanine + alpha-ketoglutarate –> pyruvate + glutamate (via alanine aminotransferase)
Pyruvate gets converted into acetyl CoA which enters TCA cycle
Glutamate is converted back to aloha-ketoglutarate by glutamate dehydrogenase
Why is NADH transport a problem?
NADH produced during glycolysis in the cytosol needs to be re-oxidised by the electron transport chain in the mitochondria
The mitochondrial membrane is impermeable to NADH so a shuttle is required
Glycerol phosphate shuttle in skeletal muscle and brain
Malate-aspartate shuttle in liver kidney and heart
What is the action of the glycerol phosphate shuttle?
NADH is re-oxidised to NAD+ and the electrons are passed onto dihydroxyacetone phosphate (DHAP)
DHAP is converted into glycerol-3-phosphate (G3P) via cytosolic glycerol-3-phosphate dehydrogenase
The electrons are transferred from G3P to FAD via mitochondrial form of the same enzyme
FADH2 is produced and DHAP is reformed
Redox reactions
What is the action of the malate-aspartate shuttle?
Aspartate undergoes transamination via alpha-ketoglutarate and forms oxaloacetate and glutamate
Oxaloacetate is reduced to malate via NADH and malate dehydrogenase
Malate is oxidised inside the mitochondria (reverse reactions occur to produce aspartate and regenerate NADH)
