Chapter 17 Lipid Biosynthesis Flashcards
Where does fatty acid catabolism take place?
in the mitochondrial matrix
Where does fatty acid catabolism take place?
in the mitochondrial matrix
Where are the electrons for fatty acid synthesis obtained from?
NADPH sourced from the pentose phosphate pathway and the malic enzyme.
Why do thioesters have high energy?
the sulfur atom is large and so there is no effective resonance taking place. Bond is weaker as a result and bond breakage is more spontaneous.
Under what conditions are fatty acids synthesized
when there is an excess of acetyl coA
What are the three stages of fatty acid synthesis?
- Preparatory: acetyl coA is transferred from mitochondria to the cytoplasm
- Activation: in cytoplasm acetyl-coA is activated, acetyl coA is converted to malonyl coA.
- Reaction: intermediates are attached to an acyl carrier protein.
In what form is acetyl-coA transported out of the mitochondria for lipid synthesis in the cytosol?
in the form of citrate, citrate is converted back into oxaloacetate and acetyl coA in the cytoplasm
What enzyme converts citrate into oxaloacetate and acetyl coA?
ATP-citrate lyase
What does citrate inhibit that affects the rate of glycolysis?
Citrate is an inhibitor of phosphofructokinase-1.
How is citrate lyase activated?
Citrate lyase is activated by phosphorylation through the insulin/PI3 Kinase/Akt Pathway.
How does the return of the carbon into the mitochondria enable the synthesis of NADPH used in lipid biosynthesis?
oxaloacetate is reduced to malate.
the malate is oxidized and decarboxylated to pyruvate generating NADPH.
What molecule is the direct precursor of fatty acid synthesis?
malonyl-coA
How many carbons are in added to the growing fatty acid chain in each round of biosynthesis?
2 carbons
What is the acetyl-coA carboxylase mechanism?
It is used to convert acetyl coA into malonyl coA in order to synthesize lipids.
What are the steps of the acetyl-coA carboxylase mechanism?
- formation of a phosphorylated bicarbonate intermediate- this reaction requires a molecule of ATP. ATP activates the bicarbonate for addition to biotin.
- The CO2 is transferred to the acetyl-coA to form malonyl coA.
Write the mechanism for the acetyl-coA carboxylase mechanism.
refer to slides
What is the first committed step of fatty acid synthesis?
synthesis of the malonyl coA
What are two sources of acetyl-coA for fatty acid biosynthesis?
mitochondrial acetyl-coA
- acetyl coA generated in the mitochondria through the breakdown of pyruvate in the pyruvate dehydrogenase complex
cytosolic acetyl coA
-citrate is transported from the mitochondria to the cytoplasm where it is converted back into acetyl coA and oxaloacetate by the enzyme citrate lyase.
What are the two fates of the oxaloacetate that is produced by the malic enzyme?
- oxaloacetate is reduced to the malate and returns to the mitochondria.
- oxaloacetate —> malate. Malate is oxidized and decarboxylated to pyruvate generating NADPH.