Lipid Catabolism Enzymes
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Biochemistry › Lipid Catabolism Enzymes
Before a fatty acid is able to undergo the beta-oxidation pathway, it must first be activated to form fatty acyl-CoA and transferred into the mitochondrial matrix from the cytoplasm of a cell via the activity of several enzymes.
What enzyme is responsible for synthesizing fatty acyl-CoA to be transported into the intermembrane space of a mitochondria?
acyl-CoA synthetase
Carnitine palmitoyl transferase I
Carnitine palmitoyl transferase II
ATP hydrolase
Citrate synthase
Explanation
Three enzymes are ultimately involved in activating fatty acids as fatty acyl-CoA and transferring this molecule into the inner mitochondrial matrix to be broken down via the beta-oxidation pathway. The first enzyme is acyl-CoA synthetase. This enzyme is a type of ATPase, and it uses the thermodynamically favorable dephosphorylation of ATP to drive the synthesis of fatty acyl-CoA from a fatty acid and CoASH. Fatty acids alone cannot cross mitochondrial membranes, but fatty acyl-CoA can cross the outer membrane.
Carnitine palmitoyl transferase II also synthesizes fatty acyl-CoA but acyl-CoA synthetase is the first enzyme to do so, and its dephosphorylation of ATP is what initially activates a fatty acid.
Which reaction in beta oxidation does hydroxyacyl-CoA dehydrogenase catalyze?
Oxidation of the beta hydroxyl group
Reduction of the beta hydroxyl group
Oxidation the gamma carbon
Dehydration of the beta carbon
Dehydration of the carbonyl carbon
Explanation
Hydroxyacyl-CoA dehydrogenase oxidizes the beta hydroxyl group, forming a carbonyl.
Fatty acyl-CoA enters the intermembrane space of a mitochondria via the enzyme acyl-CoA synthetase. Fatty acyl-CoA is the original input molecule of the beta-oxidation pathway, however, carnitine palmitoyl transferase I replaces the CoA with the molecule carnitine before being transported into the mitochondrial matrix.
Why does carnitine palmitoyl transferase replace coenzyme A with carnitine?
The carnitine carrier protein can only attach and transport fatty acylcarnitine across the inner mitochondrial membrane.
Fatty acyl-CoA is to unstable of a molecule to exist within the intermembrane space.
The reformation of fatty acyl-CoA from CoASH and fatty acylcarnitine within the mitochondrial matrix is a thermodynamically favorable reaction that drives the formation of ATP.
Carnitine is needed as an input to start the beta-oxidation pathway.
Fatty acylcarnitine can freely diffuse into the mitochondrial matrix through fatty acylcarnitine gates located on the inner mitochondrial membrane.
Explanation
The carnitine transport protein, known as the carnitine-acylcarnitine translocase, allows the facilitated diffusion of a fatty acid into the mitochondrial matrix. Fatty acids cannot be transported into the mitochondrial matrix alone.
Following this step, carnitine palmitoyl transferase II catalyzes the reaction that reforms fatty acyl-CoA from CoASH and the fatty acylcarnitine.
Which cofactor is required in the conversion of fatty acyl-CoA to trans enoyl-CoA by acyl-CoA dehydrogenase?
Biotin
Pyridoxal
Water
Explanation
What reaction does the enzyme thiolase catalyze?
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 form ketone bodies
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 break down fatty acids
Breaking apart any two thiol bonds in all reactions
Explanation
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.
What cofactor is required for the oxidation of beta-hydroxyacyl-CoA to beta-Ketoacyl-CoA by hydroxyacyl-CoA dehydrogenase?
NAD+
CoASH
FAD
NADH
FADH2
Explanation
NAD is required for the oxidation of beta-hydroxyacyl-CoA to beta-Ketoacyl-CoA by hydroxyacyl-CoA dehydrogenase.
What reaction in beta oxidation does enoyl-CoA hydratase catalyze?
The addition of water across the carbon-carbon double bond
The addition of water across the carbon-oxygen double bond
The removal of water across the carbon-carbon double bond
The removal of water across the carbon-oxygen double bond
The formation of a carbon-carbon double bond by adding water
Explanation
Enoyl-CoA hydratase catalyzes the the addition of water across the carbon-carbon double bond.
What is the primary mechanism by which fatty acid metabolism is regulated?
Acetyl-CoA carboxylase is phosphorylated, inactivating it
Acetyl-CoA carboxylase is dephosphorylated, inactivating it
Acyl-CoA dehydrogenase is phosphorylated, inactivating it
Acyl-CoA dehydrogenase is dephosphorylated, activating it
Acyl-CoA dehydrogenase is phosphorylated, activating it
Explanation
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.
What is the purpose of the enzyme cis-enoyl-CoA isomerase regarding fatty acids?
It shifts a double bond to make degradation possible
It removes a CoA group to make degradation possible
It shifts a double bond to make synthesis possible
It shifts a adds a double bond to make synthesis possible
It removes a double bond to make degradation possible
Explanation
Cis-enoyl-CoA isomerase has the important role of shifting a double bond in an unsaturated fatty acid to make the molecule degradable. Without this important enzyme, many unsaturated fatty acids would not be able to completely go through beta-oxidation.
What enzyme catalyses the shown step in beta oxidation?
L-hydroxacyl-CoA dehydrogenase
Acyl-CoA dehydrogenase
Enoyl-CoA hydratase
Acyl-CoA dehydroxylase
L-hydroxacyl-CoA dehydrogenase
Explanation
This third step in beta oxidation is catalyzed by L-hydroxacyl-CoA dehydrogenase. One way to remember is that the enzyme is named for exactly what it does: remove a hydrogen (dehydrogenate) L-hydroxyacyl-CoA (the reactant).