the citric acid cycle

march 13 + 16

in presence of O2, what does pyruvate get turned into? + why is it important? (3)

• acetyl coenzyme A (acetyl CoA)

• it is able to enter the citric acid cycle

• generates lots of NADH/FADH2 that can enter the ETC

to be aerobically metabolized, pyruvate has to be transported from the __1__ to the __2__. Here, it is __3__decarboxylated to form __4__

1. cytoplasm

2. mitochondrial matrix

3. oxidatively

4. acetyl CoA

what is the link between glycolysis and the citric acid cycle? (3)

• the irreversible conversion of pyruvate → acetyl CoA

• oxidative decarboxylation 3C → 2C

  • 2 e- go into NADH

acetyl CoA has an ____ group linked to the sulfhydryl group by a ___ bond. hydrolysis of this bond is ___ ___ = high ___ ____ ____ potential

1. acetly

2. thioester bond

3. highly exergonic

4. acetyl group transfer

describe the pyruvate dehydrogenase complex + what are the enzymes that compose it + their coenzymes?

• large enzyme complex that catalyzes the rxn

• three enzymes (E1, E2, E3)

  • allow substrates to travel from one active site to the next

what does E1 (pyruvate dehydrogenase) do + what is their coenzyme

• oxidative phosphorylation of pyruvate

• TPP

what does E2 (dihydrolipoyl transacetylase) do + what is their coenzyme

• transfer acetyl group to CoA

• lipoamide

what does E3 (dihydrolipoyl dehydrogenase) do + what is their coenzyme

• regeneration of the oxidized form of lipoamide

• FAD

What reaction does the pyruvate dehydrogenase complex catalyze?

Pyruvate → acetyl-CoA + NADH + CO₂

What is the main role of E1 in PDH?

TPP-dependent decarboxylation of pyruvate

What does lipoamide do in PDH?

Acts as a swinging arm that carries the acetyl intermediate between active sites

What are the 5 cofactors of PDH?

TPP, lipoamide, CoA, FAD, NAD⁺

What does E2 do in the PDH complex?

Transfers the acetyl group to CoA → forms acetyl-CoA

What does E3 do in the PDH complex?

Reoxidizes lipoamide and transfers electrons to NAD⁺ → makes NADH

What is the overall reaction of PDH?

Pyruvate + CoA + NAD⁺ → acetyl-CoA + CO₂ + NADH

what is occurring in stage 1 of the CAC? (2)

• oxidizes two carbon atoms

• gathers energy-rich electrons

what is occurring in stage 2 of the CAC? (3)

• regenerates oxaloacetate

• makes one ATP

• gathers energy-rich electrons