Chapter 25, Problem 25.47EP

(a)

Interpretation Introduction

Interpretation:

Whether NAD⁺ is involved in (1) glycerol metabolism to dihydroxyacetone phosphate, (2) fatty acid metabolism to acetyl CoA, or (3) both glycerol metabolism and fatty acid metabolism has to be determined.

Concept introduction:

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. The first stage of glycerol metabolism is a two-step process. After the first stage, the remaining stages of glycerol metabolism are the same as glucose pathways.  The overall equation for glycerol metabolism is as follows:

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

Fatty acids are molecules that are long hydrocarbon chain of carboxylic acid. They are building blocks of fat in humans and animals.

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 a β-oxidation pathway. Acetyl CoA, FADH₂, and NADH are produced in this pathway.

Nicotinamide adenine dinucleotide is associated with the redox reactions in metabolism. Its reduced form is NADH and oxidized form is NAD⁺.

Answer to Problem 25.47EP

NAD⁺ is involved in (3) both glycerol metabolism and fatty acid metabolism.

Explanation of Solution

The first stage of glycerol metabolism is a two-step process. In step 1, glycerol-3-phosphate is formed as the intermediate compound that further reacts to form dihydroxyacetone phosphate in step 2. The reaction for the conversion of glycerol is as follows:

Here, represents ${\text{PO}}_3^{2-}$ unit.

In step 2 of glycerol metabolism, NAD⁺ oxidized glycerol-3-phosphate to dihydroxyacetone phosphate. Therefore, NAD⁺ is involved in glycerol metabolism.

The reaction in step 3 of a turn of the β-oxidation pathway is a dehydrogenation reaction in which two hydrogen atoms are removed from L-β-hydroxyacyl CoA. In this reaction, the β-hydroxy group is converted to a β-keto group. NAD⁺ is used as an oxidizing agent. This reaction is catalyzed by β-hydroxyacyl CoA dehydrogenase enzyme. The reaction for step 3 is as follows:

Therefore, NAD⁺ is involved in (3) both glycerol metabolism and fatty acid metabolism.

(b)

Interpretation Introduction

Interpretation:

Whether ADP is involved in (1) glycerol metabolism to dihydroxyacetone phosphate, (2) fatty acid metabolism to acetyl CoA, or (3) both glycerol metabolism and fatty acid metabolism has to be determined.

Concept introduction:

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. The first stage of glycerol metabolism is a two-step process. After the first stage, the remaining stages of glycerol metabolism are the same as glucose pathways.  The overall equation for glycerol metabolism is as follows:

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

Fatty acids are molecules that are long hydrocarbon chain of carboxylic acid. They are building blocks of fat in humans and animals.

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 a β-oxidation pathway. Acetyl CoA, FADH₂, and NADH are produced in this pathway.

Adenosine diphosphate (ADP) provides energy to carry out the metabolic processes in the living cells.

Answer to Problem 25.47EP

ADP is involved in (1) glycerol metabolism to dihydroxyacetone phosphate.

Explanation of Solution

The first stage of glycerol metabolism is a two-step process. In step 1, glycerol-3-phosphate is formed as the intermediate compound that further reacts to form dihydroxyacetone phosphate in step 2. The reaction for the conversion of glycerol is as follows:

Here, represents ${\text{PO}}_3^{2-}$ unit.

In step 1 of glycerol metabolism, ATP is converted to ADP. Therefore, ADP is involved in glycerol metabolism.

(c)

Interpretation Introduction

Interpretation:

Whether kinase is involved in (1) glycerol metabolism to dihydroxyacetone phosphate, (2) fatty acid metabolism to acetyl CoA, or (3) both glycerol metabolism and fatty acid metabolism has to be determined.

Concept introduction:

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. The first stage of glycerol metabolism is a two-step process. After the first stage, the remaining stages of glycerol metabolism are the same as glucose pathways.  The overall equation for glycerol metabolism is as follows:

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

Fatty acids are molecules that are long hydrocarbon chain of carboxylic acid. They are building blocks of fat in humans and animals.

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 a β-oxidation pathway. Acetyl CoA, FADH₂, and NADH are produced in this pathway.

The transfer of a phosphoryl group $\left({\text{PO}}_3^{2-}\right)$ from adenosine triphosphate(ATP) or some other high energy phosphates to a substrate is catalyzed by a kinase enzyme.

Answer to Problem 25.47EP

Kinase is involved in (1) glycerol metabolism to dihydroxyacetone phosphate.

Explanation of Solution

The first stage of glycerol metabolism is a two-step process. In step 1, glycerol-3-phosphate is formed as the intermediate compound that further reacts to form dihydroxyacetone phosphate in step 2. The reaction for the conversion of glycerol is as follows:

Here, represents ${\text{PO}}_3^{2-}$ unit.

In step 1 of glycerol metabolism, glycerol kinase enzyme catalyzed the conversion of glycerol to glycerol-3-phosphate. Therefore, the kinase is involved in glycerol metabolism.

(d)

Interpretation Introduction

Interpretation:

Whether ketoacyl CoA is involved in (1) glycerol metabolism to dihydroxyacetone phosphate, (2) fatty acid metabolism to acetyl CoA, or (3) both glycerol metabolism and fatty acid metabolism has to be determined.

Concept introduction:

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. The first stage of glycerol metabolism is a two-step process. After the first stage, the remaining stages of glycerol metabolism are the same as glucose pathways.  The overall equation for glycerol metabolism is as follows:

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

Fatty acids are molecules that are long hydrocarbon chain of carboxylic acid. They are building blocks of fat in humans and animals.

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 a β-oxidation pathway. Acetyl CoA, FADH₂, and NADH are produced in this pathway.

Nicotinamide adenine dinucleotide is associated with the redox reactions in metabolism. Its reduced form is NADH and oxidized form is NAD⁺.

Answer to Problem 25.47EP

Ketoacyl CoA is involved in (2) fatty acid metabolism to acetyl CoA.

Explanation of Solution

The reaction in step 3 of a turn of the β-oxidation pathway is a dehydrogenation reaction in which two hydrogen atoms are removed from L-β-hydroxyacyl CoA. In this reaction, the β-hydroxy group is converted to a β-keto group. NAD⁺ is used as an oxidizing agent. This reaction is catalyzed by β-hydroxyacyl CoA dehydrogenase enzyme. The reaction for step 3 is as follows:

Therefore, ketoacyl CoA is involved in (2) fatty acid metabolism to acetyl CoA.