Biochemistry : Lipid Catabolism Enzymes
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Example Question #21 : Lipid Catabolism
Fatty acids cross the mitochondrial membrane to be degraded by beta-oxidation in the mitochondria. Which of the following statements is correct?
Fatty acid synthetase activates the fatty acid (FA) on the outer mitochondrial membrane by attaching coenzyme A (CoA)
Fatty acyl carnitine is shuttled across the mitochondrial membrane
All of these
Carnitine acyltransferase 1 attaches carnitine to fatty acids forming fatty acylcarnitine
Carnitine acyltransferase 2 removes carnitine from fatty acylcarnitine
All of these
Fatty acids are broken down in the mitochondria to produce acetyl-CoA. The process is called beta-oxidation. Acetyl-CoA is then used to produce energy via the citric acid cycle pathway. Fatty acids cannot cross the mitochondrial membrane directly without the use of the carnitine shuttle.The process described in the question represents the carnitine shuttle pathway, which allows activated fatty acids (fatty acids with CoA attached) to cross the mitochondrial membrane so they can be broken down by beta-oxidation. Fatty acid synthetase activates the fatty acid on the outer mitochondrial membrane by attaching a CoA group. Carnitine acyltransferase 1 exchanges the CoA with carnitine forming fatty acyl carnitine. Fatty acyl carnitine is shuttled across the membrane through the carnitine transporter. On the inner side of the membrane, carnitine acyltransferase 2 removes carnitine and forms fatty acid-CoA which can then be processed by beta-oxidation.
Example Question #21 : Lipid Catabolism Enzymes
What reaction does the enzyme thiolase catalyze?
Breaking apart any two thiol bonds in all reactions
Formation of acetoacetyl-CoA from two molecules of acetyl-CoA as a step to form ketone bodies
Formation of two molecules of acetyl-CoA from acetoacetyl-CoA as a step to break down fatty acids
Formation of acetoacetyl-CoA from two molecules of acetyl-CoA as a step to break down fatty acids
Formation of two molecules of acetyl-CoA from acetoacetyl-CoA as a step to form ketone bodies
Formation of acetoacetyl-CoA from two molecules of acetyl-CoA as a step to form ketone bodies
Thiolase is an enzyme that performs a reaction forming acetoacetyl-CoA from two molecules of acetyl-CoA. This reaction is the first step in the process of converting acetyl-CoA molecules to ketone bodies.
Example Question #45 : Catabolic Pathways And Metabolism
What is the primary mechanism by which fatty acid metabolism is regulated?
Acyl-CoA dehydrogenase is dephosphorylated, activating it
Acetyl-CoA carboxylase is dephosphorylated, inactivating it
Acetyl-CoA carboxylase is phosphorylated, inactivating it
Acyl-CoA dehydrogenase is phosphorylated, inactivating it
Acyl-CoA dehydrogenase is phosphorylated, activating it
Acetyl-CoA carboxylase is phosphorylated, inactivating it
Acetyl-CoA carboxylase catalyzes the committed step in fatty acid degradation - the step that forms malonyl-CoA. And so, in order to regulate fatty acid metabolism this is the enzyme that is most often controlled. Phosphorylating acetyl-CoA carboxylase inactivates it when it no longer needs to be functioning.
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