Biochemistry : Catabolic Pathways and Metabolism
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Example Questions
Example Question #1 : Lipid Catabolism
What reaction in beta oxidation does enoyl-CoA hydratase catalyze?
The removal of water across the carbon-carbon double bond
The formation of a carbon-carbon double bond by adding water
The removal of water across the carbon-oxygen double bond
The addition of water across the carbon-carbon double bond
The addition of water across the carbon-oxygen double bond
The addition of water across the carbon-carbon double bond
Enoyl-CoA hydratase catalyzes the the addition of water across the carbon-carbon double bond.
Example Question #2 : Lipid Catabolism
Which reaction in beta oxidation does hydroxyacyl-CoA dehydrogenase catalyze?
Dehydration of the beta carbon
Oxidation of the beta hydroxyl group
Dehydration of the carbonyl carbon
Reduction of the beta hydroxyl group
Oxidation the gamma carbon
Oxidation of the beta hydroxyl group
Hydroxyacyl-CoA dehydrogenase oxidizes the beta hydroxyl group, forming a carbonyl.
Example Question #7 : Lipid Catabolism
What reaction in beta oxidation does thiolase catalyze?
Cleavage of the sulfur-carbon bond
Cleavage of the sulfur-CoA bond
Cleavage of the beta-ketoacyl-CoA
Cleavage of the beta carbonyl
Cleavage of the alpha-ketoacyl-CoA
Cleavage of the beta-ketoacyl-CoA
Thiolase catalyzes the cleavage of the beta-ketoacyl-CoA.
Example Question #8 : Lipid Catabolism
What are the two major products of the thiolase-catalyzed reaction?
Acyl-CoA and a fatty acyl-CoA shortened by one carbon
Acyl-CoA and a fatty acyl-CoA shortened by two carbons
Thiol and a fatty acyl-CoA shortened by two carbons
Acetyl-CoA and a fatty acyl-CoA shortened by two carbons
Acetyl-CoA and a fatty acyl-CoA shortened by one carbon
Acetyl-CoA and a fatty acyl-CoA shortened by two carbons
The two major products of the thiolase-catalyzed reaction are acetyl-CoA and a fatty acyl-CoA shortened by two carbons.
Example Question #11 : Lipid Catabolism
The beta oxidation pathway can be described as __________.
cyclic
inhibitor-regulated
inhibitor-dependent
anabolic
linear
cyclic
The beta-oxidation pathway is cyclic. Two carbons are removed from a fatty acid chain each time it goes around the pathway. If the initial fatty acid chain has an even number of carbons then the final round of beta oxidation yields two copies of acetyl-CoA.
Example Question #12 : Lipid Catabolism
What is the final product in the beta oxidation of fatty acids with an odd number of carbons?
One copy of acetyl-CoA
Acetyl-CoA and acyl-CoA
Acetyl-CoA and propionyl-CoA
Acetyl-CoA and butyryl-CoA
Two copies of acetyl-CoA
Acetyl-CoA and propionyl-CoA
In the last round of beta oxidation, fatty acids with odd numbers of carbons will yield acetyl-CoA and Coenzyme-A attached to a fatty acid with three carbons (propionyl-CoA)
Example Question #13 : 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?
ATP hydrolase
Citrate synthase
Carnitine palmitoyl transferase II
acyl-CoA synthetase
Carnitine palmitoyl transferase I
acyl-CoA synthetase
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.
Example Question #34 : Catabolic Pathways And Metabolism
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?
Fatty acyl-CoA is to unstable of a molecule to exist within the intermembrane space.
Fatty acylcarnitine can freely diffuse into the mitochondrial matrix through fatty acylcarnitine gates located on the inner mitochondrial membrane.
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.
The carnitine carrier protein can only attach and transport fatty acylcarnitine across the inner mitochondrial membrane.
The carnitine carrier protein can only attach and transport fatty acylcarnitine across the inner mitochondrial membrane.
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.
Example Question #35 : Catabolic Pathways And Metabolism
What enzyme involved in the first step beta-oxidation pathway? What redox cofactor is formed?
Enoyl-CoA hydratase;
Acyl-CoA dehydrogenase;
Enoyl-CoA hydratase;
Acyl-CoA synthetase;
Acyl-CoA dehydrogenase;
Acyl-CoA dehydrogenase;
Acyl-CoA dehydrogenase converts fatty acyl-CoA to trans-Δ2-enoyl-CoA forming the high energy redox cofactor 
Example Question #14 : Lipid Catabolism Enzymes
What enzyme is involved with the second step of the beta-oxidation pathway, and what input molecule other than trans-Δ2-enoyl-CoA is required?
Enoyl-CoA hydratase; ATP
Carnitine palmitoyl transferase I; ATP
Enoyl-CoA hydratase;
Acyl-CoA dehydrogenase;
Acyl-CoA dehydrogenase; ATP
Enoyl-CoA hydratase;
Enoyl-CoA hydratase uses hydrates the double bond between the alpha and beta carbons of trans-Δ2-enoyl-CoA by adding a hydroxyl group to the beta carbon and a hydrogen to the alpha carbon.
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