Lipid synthesis

Question 1

Acetyl CoA carboxylase - reactants, products, importance, and required cofactor?

Answer 1

acetyl CoA + CO2 + ATP —-> malonyl CoA + ADP+ Pi
Key regulatory step in fatty acid synthesis
Biotin

Question 2

Activators and inhibitors of actetyl CoA carboxylase?

Answer 2

Activators - citrate by feeding forward, insulin acts by stimulating dephosphorylation
Inhibitors - Palmitoyl CoA (product), phosphorylation by AMP- protein kinases in response to high glucagon

*Malonyl CoA also inhibits CPT1 preventing Beta oxidation pathway

Question 3

Fatty acid synthase - reactants, products, and steps?

Answer 3

Acetyl CoA + Malonyl CoA + 2 NADPH —-> CO2, Fatty acid (+2 Carbons) CoA + 2 NADP+ + 2 H+
Eventually palmitate is formed
Bond formation, reduction, hydration, and reduction.

Question 4

How are fatty acids stored for energy as adipose?

Answer 4

Glycerol 3-phosphate head is esterified by FACoAs into triacylglyceride.

Question 5

How are fatty acids (FA) packaged, transported, and stored?

Answer 5

Dietary FA are transferred via chylomicrons. Synthesized FAs from the liver are packed as VLDL and sent into blood. At adipocyte or myocyte, VLDL is cleaved by LPLs into glyerol and free fatty acids. Free fatty acids enter the cell and glycerol is transported back to liver. Adipocytes store FA as TAG and myocytes use Beta oxidation. Free fatty acids in the blood bind to albumin for transport.

Question 6

Explain differences in lipid metabolism in liver, adipocyte, and muscle cell.

Answer 6

In the case of adipose tissue, these fatty acids may be released into the circulation for delivery to other tissues, whereas in muscle they are a substrate for oxidation and in liver they are a substrate for re-esterification within the endoplasmic reticulum to make triacylglycerol that will be secreted as very-low-density lipoprotein.