S1B4 Fatty Acid Synthesis Flashcards
What molecules allosterically activate and inhibit the acetyl-CoA carboxylase in fatty acid synthesis?
Acetyl-CoA carboxylase is allosterically activated by citrate, and inhibited by palmitoyl-CoA.
What reaction in fatty acid synthesis requires biotin? What is the energy source for the reaction?
Acetyl-CoA must be converted to malonyl-CoA prior to being added to the growing fatty acid chain. This occurs through the following reaction:
Enzyme: Acetyl-CoA carboxylase
Acetyl-CoA + CO2 → malonyl-CoA
This reaction requires biotin and ATP.
What is the rate limiting enzyme in fatty acid synthesis?
Acetyl-CoA carboxylase is the rate limiting enzyme in fatty acid synthesis.
What is the primary substrate of fatty acid synthesis?
Acetyl-CoA is the primary substrate in the repeated condensation, reduction, and dehydration reactions of fatty acid synthesis. Fatty acids are elongated by repeated addition of malonyl-CoA, which is derived from acetyl-CoA.
What are the effects of insulin and glucagon on fatty acid synthesis?
Insulin leads to dephosphorylation and activation of acetyl-CoA carboxylase, as well as upregulation of SREBP, a transcription factor involved in the production of lipogenic molecules.
Glucagon leads to phosphorylation and inactivation of acetyl-CoA carboxylase.
Where in the cell does fatty acid synthesis take place? Where in the body does it occur?
Fatty acid synthesis is a process occurring within the cytosol of:
- Hepatocytes (predominantly)
- Adipose tissue
- Lactating mammary glands
What enzyme catalyzes the elongation steps in fatty acid synthesis? What is consumed and released in each elongation cycle?
The elongation of fatty acids in fatty acid synthesis is catalyzed by fatty acid synthase. 2 NADPH are consumed and 1 CO2 is released per 2 carbon addition.
What fatty acid is produced through fatty acid synthesis? How many carbons is it?
Fatty acid synthesis ultimately produces palmitic acid, a 16 carbon fatty acid.
During well fed states, how is citrate shunted into fatty acid synthesis?
During well fed states, citrate is shunted into fatty acid synthesis as opposed to the citric acid cycle through inhibition of isocitrate dehydrogenase by ATP and NADH.
What is the purpose of the citrate shuttle? What metabolic pathway is it involved in?
The citrate shuttle is a mechanism to transport acetyl-CoA out of the mitochondria for fatty acid synthesis which takes place in the cytoplasm.
In the citrate shuttle, how is acetyl-CoA transported out of the mitochondria?
Acetyl-CoA combines with oxaloacetate to form citrate which travels across the mitochondrial membrane to the cytoplasm where it is cleaved back into oxaloacetate and acetyl-CoA.
What are the substrates in the first step in the elongation stage of fatty acid synthesis? What are the substrates in subsequent steps?
In the first step in the synthesis of the fatty acid chain, a 4 carbon saturated fatty acid is formed from acetyl-CoA and malonyl-CoA. In subsequent steps, malonyl-CoA is added to the growing chain to add 2 carbons per elongation cycle.
The elongation of fatty acids in fatty acid synthesis is catalyzed by fatty acid synthase.2 NADPHare consumed and1 CO2 is released per 2 carbon addition.
