Beta Oxidation

Overview of Beta Oxidation:-

🦨Definition:

Beta oxidation is a metabolic process during which fatty acid molecules are broken down to produce energy.

🦨Mechanism:

The process involves breaking down long fatty acids that have been converted to acyl CoA chains into progressively smaller fatty acyl-CoA chains.

🦨Products:

This reaction releases acetyl-CoA, FADH2, and NADH, which are then used in other metabolic processes, such as the citric acid cycle (Krebs cycle), to produce ATP for energy.

✓Location of Beta Oxidation:-

🦨Eukaryotic Cells: Beta oxidation takes place in the mitochondria.

🦨Prokaryotic Cells: Beta oxidation occurs in the cytosol.

✓Process of Beta Oxidation:-

1.Entry of Fatty Acids:

🦨Fatty acids must first enter the cell through the cell membrane.

🦨Once inside, they bind to coenzyme A (CoA) to form fatty acyl-CoA.

🦨In eukaryotic cells, fatty acyl-CoA is transported into the mitochondria.

2.Transport Mechanisms:

🦨Short Acyl-CoA Chains:

These can freely diffuse through the mitochondrial membrane.

🦨Long Acyl-CoA Chains:

These require transport via the carnitine shuttle.

🦨The enzyme carnitine palmitoyltransferase 1 (CPT-1), located on the outer mitochondrial membrane, converts acyl-CoA to acyl-carnitine.

🦨Acyl-carnitine is then transported across the mitochondrial membrane by carnitine translocase (CAT).

3.Inside the Mitochondria:

🦨Once inside, acyl-CoA undergoes beta oxidation to be broken down.

✓Peroxisomal Beta Oxidation:-

🦨Peroxisome Activity:

Beta oxidation in peroxisomes yields H2O2 (hydrogen peroxide) instead of FADH2 and NADH, producing heat as a byproduct.

Important Points:-

🦨Eukaryotic Cells: Beta oxidation primarily occurs in mitochondria.

🦨Prokaryotic Cells: Beta oxidation occurs in the cytosol.

🦨Transport of Long Chain Fatty Acids: Involves the carnitine shuttle and specific enzymes (CPT-1 and CAT).

🦨Energy Production: Acetyl-CoA, FADH2, and NADH produced during beta oxidation are crucial for ATP production in the citric acid cycle.

🦨Peroxisomal Differences: In peroxisomes, beta oxidation produces H2O2 and heat.

Beta Oxidation Steps:-

🪶Beta oxidation takes place in four steps: dehydrogenation, hydration, oxidation, and thiolysis.

🪶Each step is catalyzed by a distinct enzyme:

1. Dehydrogenation

🪶Reaction: Acyl-CoA is oxidized.

🪶Enzyme: Acyl-CoA dehydrogenase.

Details:

🪶A double bond is formed between the second and third carbon atoms of the acyl-CoA chain.

🪶The end product is trans-Δ2-enoyl-CoA.

🪶This step uses FAD and produces FADH2, which enters the electron transport chain to form ATP.

2. Hydration

🪶Reaction: The double bond between C2 and C3 of trans-Δ2-enoyl-CoA is hydrated.

🪶Enzyme: Enoyl-CoA hydratase.

Details:

🪶The end product is L-3-hydroxyacyl-CoA, with a hydroxyl group (OH) at C2 replacing the double bond.

🪶This step requires water.

3. Oxidation

🪶Reaction: L-3-hydroxyacyl-CoA is oxidized.

🪶Enzyme: 3-hydroxyacyl

Steps in Beta-Oxidation of Fatty Acids Third Step: Oxidation of Hydroxyl Group. In the third step, the hydroxyl group at C2 of 3-hydroxyacyl-CoA is oxidized by NAD+ in a reaction catalyzed by 3-hydroxyacyl-CoA dehydrogenase.

Production of Beta-Ketoacyl-CoA:-

🦚The process proceeds to form β-ketoacyl-CoA and NADH + H+. NADH then enters the citric acid cycle and produces ATP, which is used as energy.

Thiolysis of Beta-Ketoacyl-CoA::

🦚In the fourth step, β-ketoacyl-CoA is cleaved by a thiol group (SH) of another CoA molecule.

🦚The enzyme that catalyzes this reaction is β-ketothiolase.

End of Beta-Oxidation:-

🦚For even-numbered acyl-CoA chains, beta-oxidation ends when the entire chain is broken down into acetyl-CoA units, each containing two carbon atoms.

🦚Acetyl-CoA molecules enter the citric acid cycle to yield ATP.

Odd-Numbered Acyl-CoA Chains:-

🦚For odd-numbered acyl-CoA chains, beta-oxidation proceeds similarly except for the last step:

🦚Instead of breaking down into two acetyl-CoA molecules, a five-carbon acyl-CoA chain is broken down into a three-carbon propionyl-CoA and a two-carbon acetyl-CoA.

🦚Propionyl-CoA is then converted to succinyl-CoA, which enters the citric acid cycle to produce ATP.

Energy Yield and End Products of Beta-Oxidation:-

1.Yield per Beta-Oxidation Cycle:

1 FADH2: Produces 2 ATP.

1 NADH: Produces 3 ATP.

1 Acetyl-CoA: Produces 12 ATP.

2. Total ATP Production per Cycle:

- 1 FADH2: 2 ATP

- 1 NADH: 3 ATP

- 1 Acetyl-CoA: 12 ATP

- Total: (2 + 3 + 12 = 17) ATP

3.Actual ATP Yield:

The actual yield is approximately 12-16 ATP per beta-oxidation cycle.

✦✦✦✦✦✦✦