University:
Liberty University
Course:
BIOM 500 | Introduction to Biomedical Sciences
Academic year:

2024
Views:

390

Pages:

5
Author:

Sheha A.

Elongation Process: It involves the sequence of reactions which add 2 carbon units to the growing chain. All the reactions take place when the reactant molecule are still attached with ACP. Step 1: Acetyl CoA and Malonyl CoA condense to give β-keto acyl ACP. Reaction involves the release of CO₂. Enzyme: β-keto acyl ACP synthase. Step 2: β-keto acyl ACP → β-keto hydroxyacyl ACP Enzyme: β-keto acyl ACP reductase and NADPH + H⁺ → NADP⁺ Step 3: β-hydroxyacyl ACP → β-unsaturated acyl ACP Enzyme: hydratase with the release of H₂O Step 4: β, β unsaturated acyl ACP + NADPH + H⁺ → β-keto acyl ACP + NADP⁺ After the sequence of reaction, a four-carbon compound (butyryl ACP) is obtained which is still attached to ACP. Continuation of bonding of malonyl CoA and elongation process: 4-carbon butyrate is then transferred from the ACP to the cysteine of the residue of β-keto acyl ACP synthase complex, now ACP is vacant. Then, a new molecule of malonyl CoA binds to ACP. Then the 4 reactions are repeated so that a 6-carbon fatty acid is synthesized. This process is repeated till the 16-carbon fatty acid (palmitic acid) is formed which is still attached to ACP. Release of Palmitic Acid palmitoyl-thioesterase (deacylase) enzyme releases palmitic acid from ACP of fatty acid synthase complex palmitoyl-ACP + H₂O → palmitic acid + ACP Provide of NADPH for Fatty Acid Synthesis NADPH required for the synthesis is mainly by HMP shunt pathway malic enzyme and cytosolic isocitrate dehydrogenase enzyme also provide NADPH + H⁺ Regulation Fatty acid synthase is the catalyst enzyme of fatty acid synthesis. It is activated by citrate and inhibited by long-chain acyl-CoA like palmitoyl-CoA. Insulin induces acetyl-CoA carboxylase enzyme Glucose, epinephrine, norepinephrine and thyroxine inactivate the enzyme by promoting phosphorylation and inhibiting fatty acid synthesis. Significance Fatty acids are synthesized when there is a surplus of energy. The process of carbohydrate and amino acids are converted to fatty acids and then stored as fat.