Lipid synthesis Flashcards
What molecule is used to add carbons 2 at a time for lipid biosynthesis until palmatic acid is formed?
Acetyl CoA
What are the intermediates in the pathway linked to?
sulfhydryl group of acyl carrier protein
Citrate lyase
Enzyme that converts citrate to oxaloacetate to release an Acetyl CoA
Where does lipid biosynthesis occur?
cytosol
Citrate Shuttle
Transfers the Acetyl CoA across a membrane from the mitochondrion to the cytosol to be used for lipid synthesis
Sources for NADPH
Pentose phosphate pathway and malic enzyme
Production of Malonyl CoA is the 1st rate limiting step of lipid biosynthesis. What enzyme is used?
Acetyl CoA carboxylase.
This is an irreversible reaction
What activates Acetyl CoA Carboxylase? What inhibits it?
Activates: citrate
Inhibits: epinephrine, glucagon, and palmatic acid
What does Malonyl CoA block?
Beta oxidation carnitine shuttle
Fatty Acid Synthase
Multi-enzyme complex used in lipid biosynthesis
What piece of the FAS is the acetyl substrate from acetyl CoA added to? Which piece catalyzes the reaction?
Added to KS. Catalyzed by AT
What piece of the FAS is the malonyl substrate from malonyl CoA added to? Which piece catalyzes the reaction?
Added to ACP
Catalyzed by MT
5 steps of fatty acid synthase
- condensation: (catalyst KS) loss of CO2 from malonyl and transfers 2 carbons from acetyl CoA to malonyl ACP
- reduction: (catalyst KR) carbonyl at C3 is reduced using NADPH
- dehydration: (catalyst HD) loss of water introduces C2-C3 double bond
- reduction: (catalyst ER) reduce double bond using NADPH. Forms 4 carbon fatty acid [completes one pass of the fatty acid]
- translocation: transfer of butyryl group from ACP to KS
net reaction for fatty acid synthesis:
8 Acetyl CoA + 7 ATP + 14 NADPH + 14 H
1 palmatate + 8 CoA + 7 ADP + 7 Pi + 14 NADP + 6 H2O
2 differences between synthesis and elongation
- location (elongation in endoplasmic reticulum, synthesis in cytosol)
- carrier is CoA