Chapter 21 Lipid Biosynthesis 1. Fatty acids 2. Eicosanoids 3. Triacylglycerols 4. Membrane phospholipids 5. Cholesterol. steroids. and isoprenoids
Chapter 21 Lipid Biosynthesis 1. Fatty acids; 2. Eicosanoids; 3. Triacylglycerols; 4. Membrane phospholipids; 5. Cholesterol, steroids, and isoprenoids;
1. Fatty acid synthesis takes a different pathway from its degradation o Occurs in the cytosol(chloroplasts in plants o Acetyl-CoA provides the first two carbons which is elongated by sequential addition of two-carbon units donated from malonyl-COA o Intermediates are attached to the -sh groups of an acyl carrier protein (ACP) o NAdPh is the reductant o The enzymes are associated as a multi-enzyme complex or even being in one polypeptide chain in higher organisms(fatty acid synthase)
1. Fatty acid synthesis takes a different pathway from its degradation ⚫ Occurs in the cytosol (chloroplasts in plants). ⚫ Acetyl-CoA provides the first two carbons, which is elongated by sequential addition of two-carbon units donated from malonyl-CoA. ⚫ Intermediates are attached to the -SH groups of an acyl carrier protein (ACP). ⚫ NADPH is the reductant. ⚫ The enzymes are associated as a multi-enzyme complex or even being in one polypeptide chain in higher organisms (fatty acid synthase)
o Elongation by the fatty acid synthase complex stops upon formation of palmitate (C16), further elongation and desaturation are carried out by other enzyme systems
⚫ Elongation by the fatty acid synthase complex stops upon formation of palmitate (C16), further elongation and desaturation are carried out by other enzyme systems
2. Malonyl-CoA is formed from acetyl CoA and bicarbonate o Salih Wakil discovered that HCo3 is required for fatty acid synthesis o Acetyl-CoA carboxylase(being trimeric in bacteria. monomeric in animals and both in plants) catalyzes this carboxylation reaction The enzyme has three functional parts: a biotin carrier protein; an ATP-dependent biotin carboxylase, and a transcarboxylase. o The enzyme exemplifies a ping-pong reaction mechanism
2. Malonyl-CoA is formed from acetylCoA and bicarbonate ⚫ Salih Wakil discovered that HCO3 - is required for fatty acid synthesis. ⚫ Acetyl-CoA carboxylase (being trimeric in bacteria, monomeric in animals and both in plants) catalyzes this carboxylation reaction. ⚫ The enzyme has three functional parts: a biotin carrier protein; an ATP-dependent biotin carboxylase; and a transcarboxylase. ⚫ The enzyme exemplifies a ping-pong reaction mechanism
o This irreversible reaction commits acetyl-CoA to fatty acid synthesis
⚫ This irreversible reaction commits acetyl-CoA to fatty acid synthesis