Lecture 3 Flashcards
How many carbons enter and leave the citric acid cycle, and as what?
2 enter as Acetyl unit of Acetyl CoA.
2 leave as CO2 (oxidation).
Overview of the citric acid cycle?
Acetyl unit enters, reacts with oxaloacetate (4). Citrate (6). Isocitrate (6). -CO2 leaves a-Ketoglutarate (5). -CO2 leaves Succinyl-CoA (4). Succinate (4). Fumarate (4). Malate (4). Oxaloacetate (4).
Is citrate or oxaloacetate more oxidised? Why?
Oxaloacetate, because electrons lost to 2X CO2.
Products of the citric acid cycle?
2CO2, 8e-, GTP.
What enzyme catalyses Oxaloacetate to citrate, and how? What type of reactions are these?
Citrate synthase. Reacts Oxaloacetate and Acetyl CoA via a condensation reaction forming Citryl CoA.
Hydrolysis reaction then converts Citryl CoA to Citrate, removing CoA in the process.
What drives the Oxaloacetate to citrate reaction forward?
Hydrolysis of energy rich thioester bond.
Who discovered the citric acid cycle, and when?
Where was the discovery published?
Hans Krebs, 1937.
Enzymologia after rejection from Nature.
How many subunits is citrate synthase composed of? Are they identical?
How heavy is each subunit?
2 identical subunits.
49 kDa.
What happens when oxaloacetate binds citrate synthase?
Why is the resulting order important?
Major structural change results, causing creation of binding site for acetyl CoA.
Forces sequential binding of OAA then Acetyl CoA, preventing wasteful enzyme activity in absence of OAA.
In what form does citrate synthase bind oxaloacetate?
Where does it bind?
The open form. Binds them in the deep cleft of each monomer.
In what form does citrate synthase bind Acetyl CoA?
The closed form.
What enzyme converts citrate to isocitrate? How?
Aconite.
H2O removed in dehydration, forming cis-aconitate.
Rehydration then occurs via reaction with H2O, forming isocitrate.
What is the overall outcome of the citrate to isocitrate reaction?
Interchange of H atom and OH group.
