Lecture 29 Flashcards
What do we produce in total from beta oxidation? What is the equation?
For each round of beta oxidation we produce 1 NADH, 1 FADH2 and 1 acetyl-CoA (shorter by 2 carbons). This shorter by two carbons means it will take ( n(C)/2 - 1) rounds. This is because in the last roun two acetyl CoAs are produced. half the carbon chain will be produced in acetyl CoAs (NADH and FADH2 will be this minus 1).
What are the overall points on the citric acid cycle?
The citric acid cycle is an aerobic pathway for metabolism which oxidises acetyl-CoA. It occurs in the mitochondria and all buut one of the reactions in this process occurs in the matrix. The acetyl-CoA at this point has a two carbon chain, this is lost in the cycle. 3 NAD+ goes to 3NADH, 1 ADP + phosphate becomes ATP and 1 FAD goes to 1 FADH2.
What are the steps in the citric acid cycle? How many carbons?
The cycle starts with oxaloacetae (4C) having two carbons added to it by the acetyl-CoA in a condensation reaction to make it citrate (6C), this is dehydrated (loss of water) to cis-aconitate (6C), this is then hydrated to isocitrate (6C), then an important step the oxidative decarboxylation occurs, this loses 1 CO2 to bring it to alpha-ketoglutarate (5C), oxidative decarboxylation again to succinyl-CoA (4C), CoA-SH is then lost in substrate level phosphorylation to change the molecule to succinate (4C) and produce ATP, dehydrogenation then occurs (producing FADH2 and fumarate (4C), this is then hydrated to malate (4C), lastly this is dehydrogenated to oxaloacetate (4C) and NADH is produced. We are now back to the start.
What enzymes do the actions in the first half (loss of carbons) citric acid cycle?
Citrate synthase does the consensation of acetyl-CoA with oxaloacetate, aconitase converts citrate to isocitrate (both the dehydration and the hydration, making it susceptible to decarboxylation), Isocitrate dehydrogenase changes isocitrate (6C) to oxalosuccinate (6C) and reduces NAD+ to NADH, the oxalosuccinate is then cleaved to alpha-ketoglutarate (5C, loss of COO-) once no longer bound to the enzyme, alpha-ketoglutarate dehydrogenase (Mg2+, TPP, FAD and lipoic acid co factors, same as pyruvate dehydrogenase) (5C) changes succinyl-CoA (4C) (loss of COO- group to S-COO-). This is the first half.
What enzymes do the second half of the citric acid cycle?
Succinyl-CoA synthetase converts succinyl-CoA to succinate (loss of S-CoA hence energy release which is used to transform GTP +ADP into GDP and ATP). Succinate dehydrogenase transforms succinate to fumarate and reduces FAD to FADH2, Fumarase hydrates fumarate to L-Malate), malate dehydrogenase transforms L-Malate to oxaloacetate and reduces NAD+ to NADH.
Which reaction in the citric acid cycle occurs in the inner mitochondrial membrane?
The succinate dehydrogenase reaction is shared between the citric acid cycle and the electron transport chain, it is the only reaction done in the inner mitochondrial membrane.
What is a common poison for the citric acid cycle? Why?
The citric acid cycle is a common target for poisoning. This is done using 1080 (sodium fluoroacetate, this is because it substitutes for acetyl CoA and can be metabolised to fluorocitrate which then inhibits aconitase.
