lecture 30 - the citric acid cycle Flashcards
Where does the citric acid cycle occur?
In the mitochondrial matrix, except for one enzyme
What is the molecule that enters the citric acid cycle?
Acetyl-CoA
How many carbons enter the citric acid cycle, and in what form?
2 carbons (as acetyl-CoA)
How many carbons leave the citric acid cycle, and in what form?
2 carbons as 2 CO2 (when oxidation is complete)
In what forms is energy captured in the CAC?
1GTP (equivalent to 1 ATP), 3NADH and 1 FADH2 in each turn of the citric acid cycle.
What are the 2 key parts of the CAC?
Release of Carbon, Regeneration of the starting molecule. Energy is captured in both
What is the 2 carbon acetyl-CoA molecule entering the CAC attached to to produce a 6 carbon molecule?
Attached to a 4 carbon oxaloacetate to form a 6 carbon citrate molecule. reaction also involves water and This uses the citrate synthase molecule
Where does the energy for the condensation of acetyl-CoA with oxaloacetate come from?
the hydrolysis of CoA from acetyl CoA to produce a free CoA molecule.
What is the first reaction in the CAC that makes a 2C acetyl-CoA into a 6C citrate?
Condensation reaction with oxaloacetate, a 4 carbon molecule
What happens to citrate when it is formed at the beginning of the citric acid cycle, and why?
2 step Isomerisation involving dehydration then hydration. To make isocitrate that is susceptible to decarboxylation. Catalysed by aconitase (will be shown on exam diagram)
How does fluoroacetate interrupt the CAC?
Takes the place of acetyl-CoA and forms fluorocitrate which interrupt the aconitase enzyme
How is the first carbon removed during the CAC?
An oxidative decarboxylation reaction catalysed by isocitrate dehydrogenase (see exam diagram ) with NAD capturing energy
How is the second carbon removed in the CAC?
Second oxidative decarboxylation, where an CoA-SH group is attached to form succinyl CoA, a 4 carbon molecule. Energy captured in NADH. (similar to the pyruvate dehydrogenase reaction)
How is energy captured during the conversion of succinyl-CoA to succinate in the CAC?
Removal of CoA releases enough energy to drive the synthesis of GTP from GDP, which leads to ATP production due to equilibrium
What is the energy equivelant of GTP + ADP, which forms an equilibrium in cellular pathways?
GTP + ADP ⇌ GDP + ATP
What type of reaction is succinyl to succinate?
Substrate level phosphorylation
What are the 3 reactions of the last part of the CAC that are the same as the first 3 steps of Beta-oxidation?
Oxidation, Hydration, Oxidation
What happens during the first oxidation of succinate in the last part of the CAC?
Single bond is made to double bond. FAD to FADH
What happens during the hydration reaction of fumarate in the last part of the CAC?
Water splits across the double bond to form a hydroxyl group.
What happens during the oxidation of malate at the last part of the citric acid cycle?
Hydroxyl group converted to carboxyl group, with NAD+ forming NADH
What enzyme in the CAC is located outside of the mitochondrial matrix in the inner mitochondrial membrane?
SDH - succinate dehydrogenase
What coenzyme does SDH use in the CAC?
FAD - tightly binds to the protein
SDH is part of the CAC and what other metabolic process?
Electron transport chain (ETC)
What are the reactants of the CAC?
Acetyl-CoA + 3NAD+ + FAD + 2H2O + GDP + Pi (see exam diagram)
What are the products of the CAC?
2CO2 + CoASH + 3NADH + 3H+ + FADH2 + GTP (see exam diagram)
