Chapter 25, Problem 25.104EP

(a)

Interpretation Introduction

Interpretation:

HMG-CoA is encountered in the process (1) glycerol metabolism to dihydroxyacetone phosphate, (2) β-oxidation pathway, (3) ketogenesis, and (4) lipogenesis has to be identified.

Concept introduction:

Lipogenesis is the process employed for the synthesis of fatty acid. The starting precursor for the synthesis is acetyl CoA. The enzyme employed for the process is fatty acid synthase. It is a multienzyme complex that ties the reaction responsible for the synthesis of fatty acid. The fatty acid is synthesized in two parts. In the first part, there is citrate-malate shuttle system and in the second part, there is a cyclic process to synthesize saturated fatty acid.

The fatty acids are broken down to provide energy. The breakdown of fatty acids is a three parts process. In the first part, the fatty acid is activated. In the second part, the transportation of fatty acid into the mitochondrial matrix is facilitated by a shuttle mechanism. In the third part, the fatty acid is readily oxidized, cycling through a series of four reactions. In these series of reactions, acyl CoA is degraded to acetyl CoA. This pathway is termed as β-oxidation pathway.

Ketogenesis is a metabolic process by which ketone bodies are produced by the breakdown of fatty acids and ketogenic amino acids. This metabolic process supplies our organs with needed energy under certain circumstances such as starvation. Fatty acid molecules degrade into acetyl CoA which are utilized as reactants in the process of ketogenesis. These molecules of acetyl CoA undergo the process of condensation twice, followed by chain cleavage and hydrogenation to produce ketone bodies.

Triacylglycerol mobilization is an ongoing process in which triacylglycerols that are stored in the adipose tissue are hydrolyzed. Fatty acids and glycerol are the products of triacylglycerol mobilization. The products are released into the bloodstream.

After entering the bloodstream, the glycerol travels to the kidneys or liver. The first stage of glycerol metabolism occurs in the liver or kidney where it is converted to $\text{dihydroxyacetone phosphate}$. The overall equation for glycerol metabolism is as follows:

$\text{Glycerol}+\text{ATP}+{\text{NAD}}^{+}\to \text{Dihydroxyacetone phosphate}+\text{ADP}+\text{NADH}+{\text{H}}^{+}$

Answer to Problem 25.104EP

HMG-CoA is encountered in ketogenesis.

Explanation of Solution

HMG-CoA is produced in step 2 in ketogenesis.

Step 2 is a condensation reaction. In step 2, acetoacetyl CoA reacts with acetyl CoA and water to produce 3-hydroxyl-3-methylglutaryl (HMG-CoA) and CoA-SH. The reaction for step 2 is:

(b)

Interpretation Introduction

Interpretation:

NADPH is encountered in the process (1) glycerol metabolism to dihydroxyacetone phosphate, (2) β-oxidation pathway, (3) ketogenesis, and (4) lipogenesis has to be identified.

Concept introduction:

Lipogenesis is the process employed for the synthesis of fatty acid. The starting precursor for the synthesis is acetyl CoA. The enzyme employed for the process is fatty acid synthase. It is a multienzyme complex that ties the reaction responsible for the synthesis of fatty acid. The fatty acid is synthesized in two parts. In the first part, there is citrate-malate shuttle system and in the second part, there is a cyclic process to synthesize saturated fatty acid.

The fatty acids are broken down to provide energy. The breakdown of fatty acids is a three parts process. In the first part, the fatty acid is activated. In the second part, the transportation of fatty acid into the mitochondrial matrix is facilitated by a shuttle mechanism. In the third part, the fatty acid is readily oxidized, cycling through a series of four reactions. In these series of reactions, acyl CoA is degraded to acetyl CoA. This pathway is termed as β-oxidation pathway.

Ketogenesis is a metabolic process by which ketone bodies are produced by the breakdown of fatty acids and ketogenic amino acids. This metabolic process supplies our organs with needed energy under certain circumstances such as starvation. Fatty acid molecules degrade into acetyl CoA which are utilized as reactants in the process of ketogenesis. These molecules of acetyl CoA undergo the process of condensation twice, followed by chain cleavage and hydrogenation to produce ketone bodies.

Triacylglycerol mobilization is an ongoing process in which triacylglycerols that are stored in the adipose tissue are hydrolyzed. Fatty acids and glycerol are the products of triacylglycerol mobilization. The products are released into the bloodstream.

After entering the bloodstream, the glycerol travels to the kidneys or liver. The first stage of glycerol metabolism occurs in the liver or kidney where it is converted to $\text{dihydroxyacetone phosphate}$. The overall equation for glycerol metabolism is as follows:

$\text{Glycerol}+\text{ATP}+{\text{NAD}}^{+}\to \text{Dihydroxyacetone phosphate}+\text{ADP}+\text{NADH}+{\text{H}}^{+}$

Answer to Problem 25.104EP

NADPH is encountered in lipogenesis.

Explanation of Solution

NADPH acts as the reducing agent in step 2 and 4 of the cyclic process of lipogenesis. NADPH gets oxidized to form NADP⁺.

Step 2 involves the hydrogenation of acetoacetyl ACP to synthesis β-hydroxybutyrylwith the help of reducing agent NADPH. The reaction of this step is:

Step 4 again involves hydrogenation reaction. In this step, crotonyl ACP is converted to butyryl ACP with the help of reducing agent NADPH. The reaction of this step is:

(c)

Interpretation Introduction

Interpretation:

Malonyl ACP is encountered in the process (1) glycerol metabolism to dihydroxyacetone phosphate, (2) β-oxidation pathway, (3) ketogenesis, and (4) lipogenesis has to be identified.

Concept introduction:

Lipogenesis is the process employed for the synthesis of fatty acid. The starting precursor for the synthesis is acetyl CoA. The enzyme employed for the process is fatty acid synthase. It is a multienzyme complex that ties the reaction responsible for the synthesis of fatty acid. The fatty acid is synthesized in two parts. In the first part, there is citrate-malate shuttle system and in the second part, there is a cyclic process to synthesize saturated fatty acid.

The fatty acids are broken down to provide energy. The breakdown of fatty acids is a three parts process. In the first part, the fatty acid is activated. In the second part, the transportation of fatty acid into the mitochondrial matrix is facilitated by a shuttle mechanism. In the third part, the fatty acid is readily oxidized, cycling through a series of four reactions. In these series of reactions, acyl CoA is degraded to acetyl CoA. This pathway is termed as β-oxidation pathway.

Ketogenesis is a metabolic process by which ketone bodies are produced by the breakdown of fatty acids and ketogenic amino acids. This metabolic process supplies our organs with needed energy under certain circumstances such as starvation. Fatty acid molecules degrade into acetyl CoA which are utilized as reactants in the process of ketogenesis. These molecules of acetyl CoA undergo the process of condensation twice, followed by chain cleavage and hydrogenation to produce ketone bodies.

Triacylglycerol mobilization is an ongoing process in which triacylglycerols that are stored in the adipose tissue are hydrolyzed. Fatty acids and glycerol are the products of triacylglycerol mobilization. The products are released into the bloodstream.

After entering the bloodstream, the glycerol travels to the kidneys or liver. The first stage of glycerol metabolism occurs in the liver or kidney where it is converted to $\text{dihydroxyacetone phosphate}$. The overall equation for glycerol metabolism is as follows:

$\text{Glycerol}+\text{ATP}+{\text{NAD}}^{+}\to \text{Dihydroxyacetone phosphate}+\text{ADP}+\text{NADH}+{\text{H}}^{+}$

Answer to Problem 25.104EP

Malonyl ACP is encountered in lipogenesis.

Explanation of Solution

Malonyl ACP is the reactant in step 1 in the cyclic process in lipogenesis.

The first step involves the condensation reaction between acetyl ACP and malonyl ACP. The product formed in the first reaction is acetoacetyl ACP. The reaction of step 1 is:

(d)

Interpretation Introduction

Interpretation:

Acetoacetyl CoA is encountered in the process (1) glycerol metabolism to dihydroxyacetone phosphate, (2) β-oxidation pathway, (3) ketogenesis, and (4) lipogenesis has to be identified.

Concept introduction:

Lipogenesis is the process employed for the synthesis of fatty acid. The starting precursor for the synthesis is acetyl CoA. The enzyme employed for the process is fatty acid synthase. It is a multienzyme complex that ties the reaction responsible for the synthesis of fatty acid. The fatty acid is synthesized in two parts. In the first part, there is citrate-malate shuttle system and in the second part, there is a cyclic process to synthesize saturated fatty acid.

The fatty acids are broken down to provide energy. The breakdown of fatty acids is a three parts process. In the first part, the fatty acid is activated. In the second part, the transportation of fatty acid into the mitochondrial matrix is facilitated by a shuttle mechanism. In the third part, the fatty acid is readily oxidized, cycling through a series of four reactions. In these series of reactions, acyl CoA is degraded to acetyl CoA. This pathway is termed as β-oxidation pathway.

Ketogenesis is a metabolic process by which ketone bodies are produced by the breakdown of fatty acids and ketogenic amino acids. This metabolic process supplies our organs with needed energy under certain circumstances such as starvation. Fatty acid molecules degrade into acetyl CoA which are utilized as reactants in the process of ketogenesis. These molecules of acetyl CoA undergo the process of condensation twice, followed by chain cleavage and hydrogenation to produce ketone bodies.

Triacylglycerol mobilization is an ongoing process in which triacylglycerols that are stored in the adipose tissue are hydrolyzed. Fatty acids and glycerol are the products of triacylglycerol mobilization. The products are released into the bloodstream.

After entering the bloodstream, the glycerol travels to the kidneys or liver. The first stage of glycerol metabolism occurs in the liver or kidney where it is converted to $\text{dihydroxyacetone phosphate}$. The overall equation for glycerol metabolism is as follows:

$\text{Glycerol}+\text{ATP}+{\text{NAD}}^{+}\to \text{Dihydroxyacetone phosphate}+\text{ADP}+\text{NADH}+{\text{H}}^{+}$

Answer to Problem 25.104EP

Acetoacetyl CoA is encountered in ketogenesis.

Explanation of Solution

Step 2 is a condensation reaction. In step 2, acetoacetyl CoA reacts with acetyl CoA and water to produce 3-hydroxyl-3-methylglutaryl (HMG-CoA) and CoA-SH. The reaction for step 2 is: