FA Synthesis- Brar Flashcards
1
Q
What two pathways produce NADPH?
A
- Pentose phosphate pathway (aka hexose monophosphate shunt)
- Malic enzyme (MAIN source for FA synthesis)-Converts malate into pyruvate
2
Q
What are the 3 systems that participate in FA Synthesis?
A
- FA synthase
- FA elongase
- FA desaturase
3
Q
What is the rate limiting step of FA synthesis? What is the enzyme and what cofactors does it require (2)?
A
- Malonyl CoA
- Acetyl CoA carboxylase requires biotin and ATP to synthesize malonyl CoA
4
Q
How is acetyl CoA Carboxylase regulated?
A
- Regulated by covalent modification and allosteric means.
- Allosteric activation by citrate.
- Allosteric inactivation by long-chain fatty acyl CoA.
- Inactivated by phosphorylation in presence of glucagon.
- Activated by dephosphorylation in presence of insulin.
5
Q
What does the Fatty Acid Synthase Complex do? What does it require? What does its ACP segment contain?
A
- Adds 2 carbon units from malonyl CoA to the growing chain to form palmitate.
- After the addition of 2 carbon units the chain undergoes 2 reductions which require NADPH
- ACP has a phosphopantetheine residue
6
Q
How is FA synthesis regulated?
A
- Malonyl CoA inhibits carnitine palmitoyltransferase I (CPT I).
- Malonyl CoA levels are elevated when acetyl CoA carboxylase is activated thus mitochondrial beta oxidation is inhibited.
- This prevents a futile round of FA synthesis going on while beta oxidation is also on.
7
Q
Where does FA elongation occur? What does it require? What is the major product?
A
- Occurs in ER
- Malonyl CoA is 2 C donor
- Requires NADPH
- Major product is stearic acid
8
Q
Where does FA desaturation occur? What does it require? What is the major product?
A
- Occurs in ER
- Requires molecular oxygen, NADH and cytochrome b5
- Most commonly involves formation of a double bond b/n C9 and 10 → palmitoleic acid
- Also common is conversion of stearic acid → oleic acid
