The TCA cycle Flashcards
Oxaloacetate
Condensation reaction, to citrate by addition of acetyl coA. Enzyme citrate synthase.
Citrate
Isomersim to isocitrate by aconase
Isocitrate
Oxidative decarboxylation to alpha ketoglutarate, by isocitrate dehydrogenase. Release CO2 reduce NAD+.
Alpha-ketoglutarate
Oxidative decarboxylation to succinyl coA, by alpha ketoglutarate dehydrogenase. Release CO2 and reduce NAD+.
Succinyl CoA
Thioesterase deacetylation to Succinate by Succinate thiokinase. Produces one molecule of GTP which can be coupled to produce one ATP. Substrate level phosphorylation.
Succinate
Oxidation (not large enough to produce NADH so produces FADH2). To fumarate catalysed by succinate dehydrogenase.
Fumarate
Hydration to L-malate by fumarase
L-malate
Oxidation to oxaloacetate by malate dehydrogenase
Where does the TCA cycle occur?
Mitochondrial matrix
Describe course of glucose from outside cell to acetyl CoA in mitochondria
Enters cell and in cytoplasm becomes G6P and pyruvate (glycolysis).
Pyruvate enters through inner mitochondrial transporter.
Pyruvate converted to acetyl CoA in the link reaction.
Describe the passage of fatty acids, amino acids and ketone bodies into mitochondria
Pass through plasma membrane and mitochondrial membrane without being converted into anything (then into Acetyl CoA)
How is pyruvate converted to acetyl CoA in link reaction?
Pyruvate dehydrogenase enzyme, leads to decarboxylation, addition of CoA and oxidation (produce NADH)
What does the TCA cycle produce?
3NADH, and FADH2 for oxidation and energy yield
GTP (converted to ATP)
How is GTP formed?
Substrate level phosphorylation
How many molecules of ATP from the 3 byproducts of TCA?
10
How is FAD different from NADH?
Must be physically associated with inner mitochondrial membrane as bound to dehydrogenase
Why is it better for cyclical pathway?
Intermediates are regenerated so that net amount of each one remains same after each turn.
Intermediates present in small amounts and play catalytic role
Which steps of TCA cycle is regulated in response to ETC?
Dehydrogenase reactions
What governs the rate of TCA cycle?
ATP demand, not substrate availability
What inhibits dehydrogenase steps?
NADH, ATP
PDH is what sort of complex?
Multi enzyme
What inhibits PDH (allosteric)?
ATP, NADH, Acetyl CoA
What stimulates PDH?
ADP , NAD+, Pyruvate, CoA-SH (i.e. substrate, or products indicating low energy)
Why does high ATP inhibit PDH and high ADP stimulate PDH?
ATP Indicates high energy so need to reduce glucose usage
Lots of ADP suggests low energy situation and so upregulate PDH and glucose breakdown
