Fatty Acid Synthesis: Biosynthesis of TriAcylGlycerol (TAG)/ Triacylglycerides
Channel: YashFame
Date: 2020-06-24

TAGs are called TriAcylGlycerols/triacylglycerides. Each TAG is energy storage lipid, composed of three moles of fatty acids and one molecule of glycerol.
Acyl means the fatty acid portion that reamined after its OH group participates in esterification with glycol. Because it has thress acyl group attached with glycerol that's why it is called TriAcylGlycerol (TAG).

Fatty acid biosynthesis takes in plastids in plant cell while it occurs in cytosol of animal cell.

Enzymes that are involved in the synthesis of fatty acids are;

ACC acetyle CoA Carboxylase
Biotin that activates CO2 with the help of one mole of ATP.
Fatty acid Synthase is a multienzyme complex, consists 7 polypeptides invovled in different reactions of fatty acid synthesis.

Acyl Carrier Protein : ACP carries growing acyl group.

KS: condenses acetyl ACP and Malonyl ACP to produce beta keto acyl ACP that is why it is called keto acyl ACP synthase.

KR: Keto acyl ACP Reductase that catalysed reduction of beta keto group with the help of NADPH+H.

DH: Dehydratase releases H2O at beta Carbon 
to produce enoyl ACP.

ER: Enoyl ACP is reduced to Butyryl ACP with the help of NADPH+H, catalysed by Enoyl reductase (ER).

These enzymes completes the first cycle of acyl synthesis where in two molecules of Acetyl coA condenses to produce 4C fatty acid.

This cycle is repeated and another molecule of Malonyl ACP comes in then 2C atoms are increased to fatty acid chain.

Suppose if palmitic acid is to be synthesized then 7 reactions will take place n 8 acetyl CoA molecules are required.

After synthesis of fatty acid, glycerol is formed from Dihydroxy Acetone phosphate (DHAP) by the reduction of ketone group in which one NADPH is required.

Now three FAs are sequentially attached on the C 1, 2 n 3 of Glycerol 3 phosphate to produce TAG.