About Lesson
Biosynthesis of fatty acids
- Fatty acid synthesis occurs in the cytosol of many organisms and chloroplast ( Stroma) in plants.
- Formed by condensation of two carbon units.
- Involves a separate series of reactions to build a long chain of hydrocarbons from acetyl-CoA units.
- Uses NADPH as a reductant.
- In vertebrates, occurs in cytosol but in plants and bacteria, occurs in chloroplast.
- Mainly two enzymes are required i.e. Acetyl CoA carboxylase and Fatty acid synthetase.
Steps
- Activation:
- Synthesis starts with the formation of Acetyl ACP and malonyl ACP.
- Acetyl transacylase and malonyl transacylase catalyze these reaction
Acetyl CoA + ACP ⇌ Acetyl ACP + CoA
Malonyl CoA + ACP ⇌ Malonyl ACP + CoA
- Condensation:
- Acetyl ACP and Malonyl ACP react to form Acetoacetyl ACP.
- Reduction reaction:
- Acetoacetyl ACP is reduced to D-3-hydroxy butyryl ACP.
- Dehydration reaction:
- D-3-hydroxybutyryl ACP is dehydrated to form Crotonyl ACP.
- Reduction reaction:
- Crotonyl ACP then finally is reduced to butyryl ACP.
- This is the end of the first elongation cycle.
- In the second round, butyryl ACP condenses with malonyl ACP to form C6-β-ketoacyl ACP.
- Reduction, dehydration, and second reduction convert C6-β-ketoacyl ACP into C6-acyl ACP, ready for the third round of elongation.
- Termination:
- Process continues until a C16 palmitoyl group is formed.
