Chapter 25, Problem 25.20EP

(a)

Interpretation Introduction

Interpretation: To determine the step of glycerol metabolism in which the oxidizing agent ${\text{NAD}}^{+}$ is needed.

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:

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

Nicotinamide adenine dinucleotide is associated with the redox reactions in metabolism. Its reduced form is NADH and oxidized form is ${\text{NAD}}^{+}$.

Answer to Problem 25.20EP

The oxidizing agent ${\text{NAD}}^{+}$ is required in step 2 of glycerol metabolism.

Explanation of Solution

The first stage of glycerol metabolism is a two-step process. In step 1, $\text{glycerol 3}-\text{phosphate}$ 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, ${\text{NAD}}^{+}$ oxidized $\text{glycerol 3}-\text{phosphate}$ to dihydroxyacetone phosphate. Therefore, the oxidizing agent ${\text{NAD}}^{+}$ is needed in step 2 of glycerol metabolism.

(b)

Interpretation Introduction

Interpretation: To determine the step of glycerol metabolism in which ADP is produced.

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:

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

Adenosine triphosphate (ATP) is a triphosphate nucleotide that provide energy to carry out the metabolic processes in the living cells. It is converted either to adenosine monophosphate (AMP) or to adenosine diphosphate (ADP) after the consumption in the metabolic processes.

Answer to Problem 25.20EP

ADP is produced in step 1 of glycerol metabolism.

Explanation of Solution

The first stage of glycerol metabolism is a two-step process. The first step of glycerol metabolism requires energy that is provided by ATP. In this step, glycerol is converted to $\text{glycerol 3}-\text{phosphate}$ and ATP is converted to ADP.

The chemical reaction for step 1 is as follows:

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

Therefore, ATP is consumed in step 1 which is further converted to ADP in glycerol metabolism

(c)

Interpretation Introduction

Interpretation: To determine the step of glycerol metabolism in which $\text{glycerol 3}-\text{phosphate}$ is a reactant.

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:

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

A reactant is defined as the substance that is initially present in the chemical reaction and gets consumed to form a new substance.

Answer to Problem 25.20EP

$\text{Glycerol 3}-\text{phosphate}$ is encountered as a reactant in step 2 of glycerol metabolism.

Explanation of Solution

The first stage of glycerol metabolism is a two-step process. In step 1, $\text{glycerol 3}-\text{phosphate}$ 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.

Therefore, $\text{glycerol 3}-\text{phosphate}$ is encountered as a reactant in step 2 of glycerol metabolism.

(d)

Interpretation Introduction

Interpretation: To determine the step of glycerol metabolism in which secondary alcohol is oxidized.

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:

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

In the secondary alcohol, the carbon atom of the hydroxyl group $\left(-\text{OH}\right)$ is attached to two alkyl groups on both sides. A general structure of secondary alcohol is as follows:

Here, R and ${\text{R}}^{\text{'}}$ represents alkyl groups.

Answer to Problem 25.20EP

Secondary alcohol is oxidized in step 2 of glycerol metabolism.

Explanation of Solution

The first stage of glycerol metabolism is a two-step process. In step 1, $\text{glycerol 3}-\text{phosphate}$ 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.

$\text{Glycerol 3}-\text{phosphate}$ is secondary alcohol that is oxidized by ${\text{NAD}}^{+}$ in step 2 of glycerol metabolism. Therefore, secondary alcohol is oxidized in step 2 of glycerol metabolism.