B-Oxidation

What is beta-oxidation of fatty acids?

The catabolic degradation of FA

What is the product of beta-oxidation?

• Acetyl-CoA

• NADH

• FADH2

Where does beta oxidation occur?

Mitochondria

But if there are long chain FA, where will they go first before entering the mitochondria

Peroxisomes

What is the importance of beta-oxidation?

Provides energy source during fasting, exercise or when glucose is low

In which animals is beta-oxidation the most important

Ruminants and carnivores with fat-rich diets

What are the 3 steps of beta oxidation and where does it occur?

• Activation of fatty acids (occurs in cytosol)

• Transport into the mitochondria

• Beta-Ox cycle (occurs in mitochondrial matrix)

1. Activation of fatty acids

• What is the enzyme needed

• Why do FA need to be activated first

• How are they activated

• Requires

• Equation

• ATP converted to

Enzyme: Acyl-CoA synthetase

FA need to be activated first because: FA are inert

How activated: Converted to fatty acyl-CoA

Requires: ATP

Equation: Fatty acid + Coenzyme A + ATP —> Fatty acyl-CoA + AMP + PPi

ATP converted to: AMP which is equivalent to 2 ATP

2.Transport into the mitochondria

• Can fatty acid-CoA cross the mitochondrial membrane directly

• Describe the carnitine shuttle system

  • What converts fatty acyl-CoA to acyl-carnitine

  • How is acyl-carnitine transported into the mitochondria

  • What regenerates fatty acyl-CoA inside mitochondria

Cross directly: No fatty acyl-CoA CANNOT cross the mitochondrial membrane directly

Carnitine shuttle system:

• What converts fatty acyl-CoA to acyl-carnitine:

  • CPT-I (carnitine palmitoyltransferase I)

• How is acyl-carnitine transported into the mitochondria:

  • By carnitine-acylcarnitine translocase

• What regenerates fatty acyl-CoA inside mitochondria:

  • CPT-II (carnitine palmitoyltransferase II)

3. Beta Oxidation Cycle

• What are the 4 steps

• Each cycle removes how many carbons from FA chain

• Produces

4 steps: O-HOT

1. Oxidation: Converts fatty acyl-CoA into trans-Δ2-enoyl-CoA

2. Hydration: Converts trans-Δ2-enoyl-CoA to L-3-hydroxyacyl-CoA

3. Oxidation: Converts L-3-hydroxyacyl-CoA to B-ketoacyl-CoA

4. Thiolysis: Cleaves B-ketoacyl-CoA to release acetyl-CoA and shorter fatty acyl-CoA

Each cycle: Removes 2 carbons from FA chain

Produces: Acetyl-CoA and fatty acyl-CoA

In which steps of the beta oxidation cycle is FADH2 and NADH produced?

FADH2: Produced in the 1st oxidation step of converting acyl-CoA to trans-Δ2-enoyl-CoA

NADH: Produced in the 2nd oxidation step of converting 3-L-hydroxyacyl-CoA to B-ketoacyl-CoA

Between the 2 products produced, acetyl-CoA and fatty acyl-CoA which one is the main energy producing product?

Acetyl-CoA

So how does the acetyl-CoA produced be used for energy production?

Acetyl-CoA enters the TCA cycle by combing with oxloacetate to form citrate which stimulates a series of reactions

• This generates NADH and FADH2 which enter the ETC to produce ATP