Fatty Acid Synthesis

Question 1

Where does Fatty Acid Synthesis occur?

Answer 1

In the cytosol

Question 2

What is the substrate for fatty acid biosynthesis?

Answer 2

Acetyl-CoA, which is released into the cytosol after being paired with oxaloacetate to make citrate; upon reaching the cytosol, it breaks off of oxaloacetate (OAA is reduced to malate then malate is converted to pyruvate which is transported back into the matrix)

Question 3

Function of ATP-Citrate lyase and it’s biochemical reaction equation

Answer 3

Generates A-CoA from citrate (the carrier of A-CoA from the matrix into the cytosol) for fatty acid synthesis; reaction is Citrate+ATP+CoA-SH+water–>A-CoA+ADP+Pi+oxaloacetate

Question 4

How many NADPH do you produce from conversion of Citrate in the cytosol?

Answer 4

1 NADPH; citrate is converted to A-CoA and oxaloacetate; OAA is then reduced to malate by NADH+H and cytoplasmic malate dehydrogenase; malate then reduces NADP using malic enzyme and is decarboxylated in the process, leading to pyruvate+CO2+NADPH

Question 5

Where do all of the NADPHs come from, and how many are needed?

Answer 5

For every cycle of 2-carbon additions, 2 NADPHs are required (there are a total of 7 cycles to make a 16-C FA, palmitate) therefore 14 NADPHs will be needed; citrate makes 8 A-CoA (through CAC??) and therefore 8 NADPHs; and the other 6 NADPHs come from the pentose phosphate pathway

Question 6

What is the rate-limiting step of FA synthesis?

Answer 6

the conversion of A-CoA and carbonic acid to malonyl CoA by A-CoA Carboxylase (irreversible reaction)

Question 7

What are the regulators of A-CoA carboxylase?

Answer 7

Activated by citrate and insulin; inhibited by epinephrine, glucagon, palmitate

Question 8

What is the activate form of A-CoA carboxylase?

Answer 8

Dephosphorylated; also, if citrate binds to a phosphorylated A-CoA carboxylase, it becomes partly active

Question 9

What are the components of the Fatty Acid Synthase?

Answer 9

Acyl-Carrier Protein, Acetyl transacylase, beta-ketoacyl synthase, malonyl transacylase, beta-ketoacyl reductase, 3-hydroxyacyl dehydratase, enoyl-reductase

Question 10

Where does fatty acid elongation occur?

Answer 10

In the ER

Question 11

Where does fatty acid desaturation occur?

Answer 11

Also in the ER

Question 12

What enzyme is used to introduce double bonds into FAs?

Answer 12

delta 9 desaturase, which introduces CIS double bonds at the 9 position (between 9 and 10)