Fatty Acid Synthesis Flashcards
What is fatty acid biosynthesis
the conversion of acetyl-CoA into fatty acids in the cytoplasm using ATP and NADPH to provide the required energy
How many carbons are added to the FA chain each cycle
2 carbons
What is the source of the 2 carbons which is added to the FA chain each cycle
Acetyl CoA (from glycolysis, oxidative decarboxylation)
- from malonyl
Where does fatty acid synthesis occur
cytosol
What is the catalyst for FA synthesis
A multi protein complex - Acyl Carrier Protein (ACP-SH)
What is a Acyl Carrier Protein (ACP)
The acyl carrier protein has a side chain that binds to the growing fatty acid, and rotates it in a merry go mechanism over the active areas of the different enzymes for each step.
rotates clock-wise
- a different step is catalyzed by the enzyme system in each sphere
The “swinging arm” side chain is a phosphopantatheine prosthetic group
What is a prosthetic group
The non-protein component of a protein complex
What molecules are consumed in the FA synthesis cycle
Acetyl-CoA,
ATP
NADPH
What is the end product of FA synthesis
C16 palmitic acid
What is the initial substance in FA synthesis
Acetyl - CoA
How many steps are there in FA synthesis
6
What is step 1 of FA synthesis
Priming of the system of Acetyl-CoA
- grafting a C2 fragment onto the acyl carrier protein (ACP)
What is step 2 (a) of FA synthesis
Malonyl-CoA is synthesized
Requires ATP
this doesn’t involve the product from step 1
What is step 2 (b) of FA synthesis
Loading of the malonyl-ACP complex to form malonyl-ACP
What is step 3 of FA synthesis
Condensation reaction;
The products from step 1 and 2 are joined together
An unfavorable reaction driven by the energy from high energy thiol-ester bond from the being hydrolyzed
Decarboxylation - Loss of CO2
What is step 4 of FA synthesis
Reduction Reaction
The ketone group is reduced to an alcohol.
Driven energetically by the NADPH oxidation (NADPH is a stronger reducing agent than NADH)
What is step 5 of FA synthesis
dehydration reaction (water is removed)
What is step 6 of FA synthesis
the second reduction driven by NADPH oxidation
What happens after step 6 in FA synthesis
The cycle then repeats but used butyryl-ACP as the starting substrate.
Another Malonyl-ACP is synthesized and grafted onto butyryl-ACP and them it goes through step 3-6 again
In mammals the cycle keeps going around adding C2 each time until C16 palmitic acid is reached
How many FA synthesis cycles is required to form Palmitic Acid (C16)
7 cycles
Which steps are reduction reactions in FA synthesis
Step 4 and Step 6
What type of reaction is step 3
condensation
What type of reaction is step 5
dehydration
What are the general reaction for each step in FA synthesis
- Acetyl ACP synthesis - priming of the system by acetyl-CoA
- a) Malonyl CoA synthesis (requires ATP)
b) Malonyl ACP synthesis - Condensation
- Reduction
- Dehydration
- Reduction
How many NADPH is used each cycle
2
What step requires ATP hydrolysis
Step 2 (a)
formation of malonyl-CoA
How much ATP is required per cycle
1
used to form Malonyl in step 2
What reaction is a decarboxylation and CO2 is loss
Step 3 - Condensation of Acetyl-ACP and Malonyl-ACP
What is the general reaction for each step
- Priming the system
- Malonyl-ACP synthesis
- Condensation
- Reduction
- Dehydration
- Reduction
At what steps is NADPH oxidized
Step 4 and 6 (every reduction reaction)
What is the net equation
What molecule is this
NADP+
What are the differences between FA synthesis and b-oxidation
- FA synthesis involves reductions reactions where b-oxidaiton involves oxidation reactions
- FA synthesis occurs in the cytoplasm while b-oxidaiton occurs in the mitochondrial matrix
- FA synthesis has 6 steps while b-oxidation has 5 steps
- FA synthesis produces palmitate while B-oxidation produces acetyl-CoA
- FA synthesis adds 2 carbon atoms at a time while b-oxidation cleaves 2 carbon atoms at a time
