19: Citric Acid Cycle

CAC oxidizes acetyl fragment of acetyl CoA → [?]

CO2

By the end of 1st stage, what’s generated?

2 CO2 by oxidative decarboxylation

DEFINE: Step 1

Citrate synthase catalyzes the condensation of acetyl CoA + oxaloacetate to form citrate

DEFINE: Citrate synthase

DEFINE: Step 2

Aconitase catalyzes the formation of isocitrate from citrate

What is Aconitase inhibited by?

Metabolite fluoroacetate (suicide inhibitor), found in the genus Gastrolobium

DEFINE: Step 3

Isocitrate dehydrogenase catalyzes the oxidative decarboxylation of
isocitrate, forming α-ketoglutarate (5C) & capturing high-energy electrons
as NADH; 1st NADH and CO2 formed

DEFINE: Step 4

α-ketoglutarate dehydrogenase complex catalyzes the synthesis of
succinyl CoA (4C) from α-ketoglutarate generating NADH

DEFINE: Step 5

Start of 2nd Stage of Cycle; Succinyl CoA synthetase catalyzes the cleavage of a thioester linkage & concomitantly forms ATP

What powers the formation of ATP?

Cleavage of thioester of succinyl CoA

Bc succinyl CoA synthetase forms donates a phosphate to ADP, it makes this an example of

Substrate-lvl phosphorylation

DEFINE: Step 6-8

Succinate dehydrogenase, fumarase, & malate
dehydrogenase catalyze successive reactions to regenerate
oxaloacetate

What’s generates in Step 6?

FADH2

What’s generated in Step 8?

NADH

e- from NADH will generate how much ATP?

2.5

e- from FADH2 will generate how much ATP?

1.5

How many acetyl CoA are produced from glu? (Hint: how many pyruvates are made by 1 glu)

2

NET RXN OF CAC

IDENITFY: Key control points in CAC

isocitrate dehydrogenase & (alpha)-ketoglutarate dehydrogenase

What controls entry of glu-derived acetyl CoA into the cycle?

Pyruvate dehydrogenase

What are replenishing rxns also called?

Anaplerotic

Similar to CAC, the Glyoxylate Cycle allows carbohydrate synthesis from

Fats, bypassing the 2 decarboxylation steps

In Glyoxylate Cycle, Succinate can be converted into

Oxaloacetate & then into glu