Chapter 25, Problem 25.29EP

(a)

Interpretation Introduction

Interpretation: To determine the functional group change that occurs in step 1 of a turn of the $\beta -\text{oxidation}$ pathway.

Concept introduction: The $\beta -\text{oxidation}$ pathway is defined as a repetitive series of four biochemical reactions in which $\text{acyl CoA}$ is degraded to $\text{acetyl CoA}$ by the removal of two carbon atoms at a time. NADH and ${\text{FADH}}_2$ are also produced in this pathway.

Functional groups are defined as the group of atoms which are attached to the carbon backbone of organic compounds. These are generally heteroatoms which are attached to the parent hydrocarbon chain. Some examples of functional groups are as follows:

Here, R and ${\text{R}}^{\text{'}}$ represent an alkyl group. In alkene, ${\text{R}}_1$, ${\text{R}}_2$, ${\text{R}}_3$ , and ${\text{R}}_4$ can be the same or different or can be hydrogen.

Alkanes are saturated hydrocarbons that contain covalently bonded hydrogen and carbon atoms.

Answer to Problem 25.29EP

In step 1 of a turn of the $\beta -\text{oxidation}$ pathway, an alkane is converted to an alkene.

Explanation of Solution

The reaction in step 1 of a turn of the $\beta -\text{oxidation}$ pathway is a dehydrogenation reaction in which hydrogen atoms from the $\alpha$ and $\beta$ carbons of $\text{acyl CoA}$ are removed; a double bond is formed between $\alpha$ and $\beta$ carbons. FAD oxidizes $\text{acyl CoA}$. This reaction is catalyzed by $\text{acyl CoA dehydrogenase}$ enzyme. The reaction for step 1 is as follows:

Therefore, $\text{acyl CoA}$ is converted to $\text{trans-enoyl CoA}$. The functional group in $\text{acyl CoA}$ and $\text{trans-enoyl CoA}$ are represented as follows:

Carbon atoms are bonded with other carbon atoms by a single covalent bond in $\text{acyl CoA}$, therefore; it is an alkane. A double bond is present in $\text{trans-enoyl CoA}$, therefore; it is an alkene. Hence, in step 1 of a turn of the $\beta -\text{oxidation}$ pathway, an alkane is converted to an alkene.

(b)

Interpretation Introduction

Interpretation: To determine the functional group change that occurs in step 2 of a turn of the $\beta -\text{oxidation}$ pathway.

Concept introduction: The $\beta -\text{oxidation}$ pathway is defined as a repetitive series of four biochemical reactions in which $\text{acyl CoA}$ is degraded to $\text{acetyl CoA}$ by the removal of two carbon atoms at a time. NADH and ${\text{FADH}}_2$ are also produced in this pathway.

Functional groups are defined as the group of atoms which are attached to the carbon backbone of organic compounds. These are generally heteroatoms which are attached to the parent hydrocarbon chain. Some examples of functional groups are as follows:

Here, R and ${\text{R}}^{\text{'}}$ represent an alkyl group. In alkene, ${\text{R}}_1$, ${\text{R}}_2$, ${\text{R}}_3$ , and ${\text{R}}_4$ can be the same or different or can be hydrogen.

Alkanes are saturated hydrocarbons that contain covalently bonded hydrogen and carbon atoms. In secondary alcohol, the carbon atom of the hydroxyl group $\left(\text{OH}\right)$ is bonded to alkyl groups on both sides.

Answer to Problem 25.29EP

In step 2 of a turn of the $\beta -\text{oxidation}$ pathway, an alkene is converted to $2°\text{ alcohol}$.

Explanation of Solution

The reaction in step 2 of a turn of the $\beta -\text{oxidation}$ pathway is a hydration reaction. In step 2, a water $\left({\text{H}}_2\text{O}\right)$ molecule is added across the trans double bond in $\text{trans-enoyl CoA}$, therefore; secondary alcohol is produced at $\beta$ carbon. This reaction is catalyzed by $\text{enoyl CoA hydratase}$ enzyme. The reaction for step 2 is as follows:

Therefore, $\text{acyl CoA}$$\text{trans-enoyl CoA}$ is converted to $\text{L-}\beta \text{-hydroxyacyl CoA}$. The functional group in $\text{trans-enoyl CoA}$ and $\text{L-}\beta \text{-hydroxyacyl CoA}$ are represented as follows:

A double bond is present in $\text{trans-enoyl CoA}$, therefore; it is an alkene. In $\text{L-}\beta \text{-hydroxyacyl CoA}$, the carbon atom of the hydroxyl group $\left(\text{OH}\right)$ is bonded to alkyl groups on both sides. Hence, it is a $2°\text{ alcohol}$. Therefore, in step 2 of a turn of the $\beta -\text{oxidation}$ pathway, an alkene is converted to $2°\text{ alcohol}$.

(c)

Interpretation Introduction

Interpretation: To determine the functional group change that occurs in step 3 of a turn of the $\beta -\text{oxidation}$ pathway.

Concept introduction: The $\beta -\text{oxidation}$ pathway is defined as a repetitive series of four biochemical reactions in which $\text{acyl CoA}$ is degraded to $\text{acetyl CoA}$ by the removal of two carbon atoms at a time. NADH and ${\text{FADH}}_2$ are also produced in this pathway.

Functional groups are defined as the group of atoms which are attached to the carbon backbone of organic compounds. These are generally heteroatoms which are attached to the parent hydrocarbon chain. Some examples of functional groups are as follows:

Here, R and ${\text{R}}^{\text{'}}$ represent an alkyl group. In alkene, ${\text{R}}_1$, ${\text{R}}_2$, ${\text{R}}_3$ , and ${\text{R}}_4$ can be the same or different or can be hydrogen.

Alkanes are saturated hydrocarbons that contain covalently bonded hydrogen and carbon atoms. In secondary alcohol, the carbon atom of the hydroxyl group $\left(\text{OH}\right)$ is bonded to alkyl groups on either side.

Answer to Problem 25.29EP

In step 3 of a turn of the $\beta -\text{oxidation}$ pathway, $2°\text{ alcohol}$ is converted to a ketone.

Explanation of Solution

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

Therefore, $\text{L-}\beta \text{-hydroxyacyl CoA}$ is converted to $\beta \text{-ketoacyl CoA}$. The functional group in $\text{L-}\beta \text{-hydroxyacyl CoA}$ and $\beta \text{-ketoacyl CoA}$ are represented as follows:

In $\text{L-}\beta \text{-hydroxyacyl CoA}$, the carbon atom of the hydroxyl group $\left(\text{OH}\right)$ is bonded to alkyl groups on both sides. Hence, it is a $2°\text{ alcohol}$. Carbonyl group in $\beta \text{-ketoacyl CoA}$ is bonded to alkyl groups on both sides, hence; it is a keto compound. Therefore, in step 3 of a turn of the $\beta -\text{oxidation}$ pathway, $2°\text{ alcohol}$ is converted to a keto group.