Final-Ch.24

Where does fatty acid (fa) biosynthesis occur in the cell?

In the cytosol

Describe the strategy of lipid synthesis.

1. Fatty acid chains are constructed by the addition of two-carbon units derived from acetyl-CoA. 2. The acetate units are activated by formation of malonyl-CoA (at the expense of ATP). 3. The addition of two-carbon units to the growing chain is driven by the decarboxylation of malonyl-CoA. 4. The elongation reactions are repeated until the growing chain reaches 16 carbons in length (palmitic acid). 5. Other enzymes then add double bonds and additional carbon units to the chain.

How is lipid synthesis different from lipid breakdown?

1. Intermediates in fatty acid synthesis are linked covalently to the sulfhydryl groups of special proteins, the acyl carrier proteins. In contrast, fatty acid breakdown intermediates are bound to the -SH group of coenzyme A. 2. Fatty acid synthesis occurs in the cytosol, whereas fatty acid degradation takes place in mitochondria. 3. In animals, the enzymes of fatty acid synthesis are components of one long polypeptide chain, the fatty acid synthase, whereas no similar association exists for the degradative enzymes. 4. The coenzyme for the oxidation-reduction reactions of fatty acid synthesis is NADP+/NADPH, whereas degradation involves the NAD+/NADH couple.

Give the overall reaction of this acetyl CoA palmitoyl CoA conversion.

8 Acetyl CoA + 7 ATP + 14 NADPH+ 7 H+ -> Palmitoyl CoA + 14 NADP+ + 7 CoASH + 7 ADP + Pi

Give the net reaction for conversion of Acetyl CoA to palmitate.

Acetyl CoA + 7 Malonyl CoA + 14 NADPH +13 H+ + H2O -> Palmitate +7 HCO3- + 8CoASH + 14NADP+

What are the sources (compounds or pathways) of acetyl CoA in the cell (Fig. 24.1 and notes)?

Amino Acid degradition, fatty acid oxidation in mitochondria, glycolysis, and use citrate-malate-pyruvate shuttle to get needed substrate to cytosol.

Describe the regulation of acetyl CoA carboxylase activity (Fig. 24.5 and notes, name the 2 allosteric regulators).

Palmitoyl-CoA is the final product of fatty acid biosynthesis, shifts the equilibrium toward the inactive protomers, whereas citrate, an important allosteric activator of this enzyme, shifts the equilibrium toward the active polymeric formof the enzyme.

Where does NADPH needed for fatty acid biosynthesis come from?

Pentose Phosphate Pathway (Malic enzyme reaction)

What is the carrier for fa biosynthesis and name the prosthetic group (Fig. 24.6, don't have to draw it).

The basic building blocks of fatty acid synthesis are acetyl and malonyl groups that are first passed to acyl carrier protein (or simply ACP). This protein is attached, on a serine residue, a phosphantetheine group, the same group that forms the "business end" of coenzyme A, specialized for use in fatty acid biosynthesis.