Beta Oxidation

Once the fatty acyl- CoA is inside the matrix what happens?

It undergoes beta oxidation

Overview of beta oxidation function

• Chops the fatty acid two carbons at a time (from the carboxyl end).

• Releases acetyl-CoA, which can enter the citric acid cycle.

• Generates NADH and FADH₂, which go to the electron transport chain for ATP production.

Beta oxidation cosists of four continuous steps:

1. Oxidation → makes a double bond

2. Hydration → adds water

3. Oxidation → makes a ketone

4. Thiolysis → cuts off acetyl-CoA (2 carbons)

• happens each time the fatty acid is shortened by 2 carbons in β-oxidation.

Step 1 beta oxidation:

Oxidation by FAD forms a double bond between the alpha and Beta carbons of fatty acyl-CoA (alkane → alkene)

• you can see which is alpha (the one beside the carbonyl carbon) thats where

• In this process we lose two hydorgens and these 2 hydorgens are used to convert FAD to FADH2.

Step 2 Beta oxidation

Water is added across the double bond to give an alcohol at the beta carbon (hydration → alkene → alcohol)

• the double bond is back to saturated

Step 3: Beta oxidation

Oxidation of the alcohol by NAD+ this this causes loss of 2 hydrogens and a ketone at beta carbon

• NAD+ becomes NADH + H

Step 4 beta oxidation:

Lysis of the bond between alpha and beta carbons (thiolysis) a sulfer group is added ot do this

• Another Acetyl coA comes in attacks the Beta carbon ketone

• Now fatty acid is shortened by 2

• the cycle can contineu and shorten the next fatty acids on the chain

• left with 2 products Acetyl-CoA which is the part in orange attached to the S (2 carbons)

• the original fatty acid minus two carvbons

Acyl-CoA vs Acetyl-CoA

• Acyl-CoA = any length fatty acid attached to CoA → what we start with

• Acetyl-CoA = the 2-carbon version (final product of β-oxidation)

Each round of β-oxidation does 4 steps (oxidation, hydration, oxidation, thiolysis) and:

• Releases 1 acetyl-CoA (2 carbons)

• Shortens the fatty acid by 2 carbons

When does beta oxidation end?

when the entire fatty acid chain is converted into acetyl-CoA units

Palmitic acid Beta oxidation example → 16 carbon fatty acid

requires 7 cycles - BECAUSE IT HAPPENS BETWEEN THE BONDS

16/2-1=7

What does each cycle of Beta oxidation release?

• 1 FADH₂

• 1 NADH
  These coenzymes enter the electron transport chain to produce ATP.

What happens after beta oxidation?

• The acetyl-CoA produced enters the citric acid cycle (Krebs cycle) where it is further oxidized to CO₂, producing additional GTP, NADH, and FADH₂, contributing further to cellular energy.

If you know the number of carbon atoms in a fatty acid (e.g., 16), how can you calculate the number of acetyl-CoA, NADH, and FADH₂ molecules produced during β-oxidation?

1. Acetyl CoA → divide 16 by 2

2. NADH and FADH2 would be would ever 16/2 is - 1

Complete beta oxidation of a 20-carbon saturated fatty acid will yield:

10 acetyl coA; 9 NADH, 9 FADH2