Citric Acid Cycle and Oxidative Phosphorylation

What does the citric acid cycle allowed for?

All carbon sources to be oxidized

What happens when 2 C acetyl group reacts with 4C oxaloacetate?

6C Citrate is formed

Can citrate be converted back into oxaloacetate?

Yes, oxaloacetate → citrate is a reversible reaction

What is lost when citrate is formed?

• 2 CO2

• Electrons (NADH & FADH2)

Where is CO2 Lost in the Citric Acid Cycle

• Isocitrate → a-ketoglutarate

• a-ketoglutarate → Succinyl CoA

Products of the Citric Acid Cycle

• 3 molecules of NADH

• 1 molecule of FADH2

Why is CoA recycled?

To use for the synthesis of more acetyl CoA

Enzymes of the Citric Acid Cycle

• Soluble

• Located within the matrix

What does solubilization of the mitochondria release?

A multi-enzyme complex containing the soluble enzymes of the citric acid cycles

What is the advantage of the multi-enzyme complex?

products pass from one enzyme to the next without the need for substantial diffusion

• More efficient

Acetyl CoA and Oxaloacetate Combine

Isomerisation of Citrate

Oxidation of isocitrate of alpha ketoglutarate

Succinyl CoA Formation

Succinyl CoA to Succinate

Regeneration of Oxaloacetate

What does the citric acid cycle generate?

NADH & FADH2

Where do the electrons from NADH and FADH2 go?

Transferred to O2 via the electron transport complexes

What does the Electron Transport Complex do?

Transports H+ out of the matrix

How is ATP generated?

F0F1 ATPase complex used the H+ gradient

What can fats and amino acids be used for?

Generating ATP

What does the breakdown of Triglycerides produce?

Fatty acids and glycerol

Are fatty acids are a predominant energy source?

Yes, in many tissues including cardiac muscle cells

What does the oxidation of NADH and FADH2 generate?

A Proton Motive Force

What happens to most of the energy produced when biological fuels are oxidised to CO₂?

Most of the energy is used to reduce NAD⁺ and FAD into NADH and FADH₂.

What is the oxidation of biological fuels coupled to?

The Reduction of O2

Reduction of O2

NADH + H+ + 1/2 O2 → NAD+ + H2O

FADH2 + 1/2 O2→FAD + H2O

What is the energy released from NADH and FADH₂ used for in the mitochondria?

It is coupled to the transfer of electrons across the inner mitochondrial membrane (IMM)

What does the transfer of electrons across the inner mitochondrial membrane produce?

the proton motive force → drives ATP synthesis

What does electron Transport Generate?

A proton gradient

What does the proton motive force generate the ETC drive?

ATP synthesis via ATP synthase

Mechanism of ATP Synthesis

1. Flow of proton through Fo motor

2. Rotation of the ring of c subunits

3. C ring rotation

4. Gamma rotation

5. Conformational change in beta subunit

6. ATP synthesis

Location of ATP Synthesis in Bacteria

aerobic bacteria plasma membrane

Location of ATP Synthesis in Eukaryotes

mitochondrial inner membrane

Location of ATP Synthesis in Plants

chloroplast thylakoid membrane

ETC Complex 1

• two electrons are carried to the first complex aboard NADH

• Transfers e^- to ubiquinone

• Enzyme = NADH dehydrogenase

• Pumps 4 hydrogen ions across the membrane to intermembrane space

ETC Complex II

Directly Receives FADH2 which does not pass through complex I

Ubiquinone

moves electrons from complexes I and II to complex III

ETC Complex III

• Accepts electrons from reduced ubiquinol

• Transfers electrons to cytochrome c

ETC Complex IV

• Receives electrons from cytochrome c

• Reduced oxygen to water

• Pumps protons across the inner membrane to create a gradient for ATP synthesis