Chapter 23, Problem 23.44EP

(a)

Interpretation Introduction

Interpretation: To classify each of the following molecules as (1) an oxidizing agent, (2) a reducing agent, or (3) neither an oxidizing agent nor a reducing agent.

a. NADH

b. ATP

c. FAD

d. CoA–SH

Concept introduction: The sum of various chemical reactions occurring in the human body is called metabolism and the reactions individually are known as metabolic reactions. During these metabolic reactions, the various metabolic intermediates are formed for the short time to complete the reactions.ATP,$\text{FAD}$,$\text{NADH}$ and CoA–SH are examples of a metabolic intermediate.

$\text{NADH}$ is the reduced form of nicotinamide adenine dinucleotide. It is employed asan oxidizing agent in various reactions like oxidation of secondary alcohol into a ketone. Its structure consists of three subunits: nicotinamide, ribose,and ADP.

ATP is a nucleotide which provides energy for the completion of various metabolic reactions occurring in our human body. The structure of ATP consists of adenine base, ribose sugar unit and the three phosphate groupconnected to each other by phosphoanhydride bonds.

Flavin adenine dinucleotideexists in two forms: oxidized form $\left(\text{FAD}\right)$ and reduced form $\left({\text{FADH}}_2\right)$. The main function of flavin adenine dinucleotide is to act as an oxidizing agent and used by the cell in oxidation reactions like oxidation of fatty acid.

Coenzyme A (CoA) is a coenzyme which is utilized in various metabolic reactions. The functions of coenzyme A include oxidation of pyruvate in the citric cycle and fatty acid oxidation.

Oxidizing agents are those species which gets reduced and oxidizes the other species present in the chemical reaction. Reducing agent is those species which gets oxidized and reduces the other species present in a chemical reaction. Generally, oxidizing agents are electron acceptor and reducing agents are electron donor.

Answer to Problem 23.44EP

$\text{NADH}$ acts as a reducing agent in metabolic reactions.

Explanation of Solution

Nicotinamide adenine dinucleotide exists in two forms: $\text{NADH}$ and ${\text{NAD}}^{+}$. The structure consists of three subunits: nicotinamide, ribose, and ADP. The redox reaction that occurs in metabolic pathways for the conversion of $\text{NADH}$ to ${\text{NAD}}^{+}$ is:

$\text{NADH}+{\text{H}}^{+}\to {\text{NAD}}^{+}+2{\text{H}}^{+}+2e^{-}$

Here $\text{NADH}$ is undergoing oxidation by a loss of two electrons and converted into ${\text{NAD}}^{+}$. Hence $\text{NADH}$ molecule acts as a reducingagent.

(b)

Interpretation Introduction

Interpretation: To classify each of the following molecules as (1) an oxidizing agent, (2) a reducing agent, or (3) neither an oxidizing agent nor a reducing agent.

a. NADH

b. ATP

c. FAD

d. CoA–SH

Concept introduction: The sum of various chemical reactions occurring in the human body is called metabolism and the reactions individually are known as metabolic reactions. During these metabolic reactions, the various metabolic intermediates are formed for the short time to complete the reactions.ATP,$\text{FAD}$,$\text{NADH}$ and CoA–SH are examples of a metabolic intermediate.

$\text{NADH}$ is the reduced form of nicotinamide adenine dinucleotide. It is employed asan oxidizing agent in various reactions like oxidation of secondary alcohol into a ketone. Its structure consists of three subunits: nicotinamide, ribose,and ADP.

ATP is a nucleotide which provides energy for the completion of various metabolic reactions occurring in our human body. The structure of ATP consists of adenine base, ribose sugar unit and the three phosphate groupconnected to each other by phosphoanhydride bonds.

Flavin adenine dinucleotideexists in two forms: oxidized form $\left(\text{FAD}\right)$ and reduced form $\left({\text{FADH}}_2\right)$. The main function of flavin adenine dinucleotide is to act as an oxidizing agent and used by the cell in oxidation reactions like oxidation of fatty acid.

Coenzyme A (CoA) is a coenzyme which is utilized in various metabolic reactions. The functions of coenzyme A include oxidation of pyruvate in the citric cycle and fatty acid oxidation.

Oxidizing agents are those species which gets reduced and oxidizes the other species present in the chemical reaction. Reducing agent is those species which gets oxidized and reduces the other species present in a chemical reaction. Generally, oxidizing agents are electron acceptor and reducing agents are electron donor.

Answer to Problem 23.44EP

ATP molecule is neither a reducing agent nor an oxidizing agent in metabolic reactions.

Explanation of Solution

Adenosine triphosphate (ATP) is anucleotide which structural component is one unit of the adenine base, one unit of ribose sugar and three units of a phosphate group. It can be converted into its monophosphate form(AMP) and diphosphate form(ADP) by losing a phosphate group. The reaction to this change is:

$\begin{array}{c}\text{ATP }+{\text{ H}}_2\text{O}\to \text{AMP }+{\text{ 2P}}_{\text{i}}+2{\text{H}}^{+}+\text{energy}\\ \text{ATP }+{\text{ H}}_2\text{O}\to \text{ADP }+{\text{ P}}_{\text{i}}+{\text{H}}^{+}+\text{energy}\end{array}$

Here ATP is not involved in electron transfer hence it is neither a reducing agent nor an oxidizing agent.

(c)

Interpretation Introduction

Interpretation: To classify each of the following molecules as (1) an oxidizing agent, (2) a reducing agent, or (3) neither an oxidizing agent nor a reducing agent.

a. NADH

b. ATP

c. FAD

d. CoA–SH

Concept introduction: The sum of various chemical reactions occurring in the human body is called metabolism and the reactions individually are known as metabolic reactions. During these metabolic reactions, the various metabolic intermediates are formed for the short time to complete the reactions.ATP,$\text{FAD}$,$\text{NADH}$ and CoA–SH are examples of a metabolic intermediate.

$\text{NADH}$ is the reduced form of nicotinamide adenine dinucleotide. It is employed asan oxidizing agent in various reactions like oxidation of secondary alcohol into a ketone. Its structure consists of three subunits: nicotinamide, ribose,and ADP.

ATP is a nucleotide which provides energy for the completion of various metabolic reactions occurring in our human body. The structure of ATP consists of adenine base, ribose sugar unit and the three phosphate groupconnected to each other by phosphoanhydride bonds.

Flavin adenine dinucleotideexists in two forms: oxidized form $\left(\text{FAD}\right)$ and reduced form $\left({\text{FADH}}_2\right)$. The main function of flavin adenine dinucleotide is to act as an oxidizing agent and used by the cell in oxidation reactions like oxidation of fatty acid.

Coenzyme A (CoA) is a coenzyme which is utilized in various metabolic reactions. The functions of coenzyme A include oxidation of pyruvate in the citric cycle and fatty acid oxidation.

Oxidizing agents are those species which gets reduced and oxidizes the other species present in the chemical reaction. Reducing agent is those species which gets oxidized and reduces the other species present in a chemical reaction. Generally, oxidizing agents are electron acceptor and reducing agents are electron donor.

Answer to Problem 23.44EP

$\text{FAD}$ molecule acts as an oxidizing agent in metabolic reactions.

Explanation of Solution

Flavin adenine dinucleotide exists in two forms: $\text{FAD}$ and ${\text{FADH}}_2$. The structure consists of three subunits: Flavin, ribitol and ADP. The redox reaction that occurs in metabolic pathways for the conversion of $\text{FAD}$ to ${\text{FADH}}_2$ is:

$\text{FAD}+2{\text{H}}^{+}+2e^{-}\to {\text{FADH}}_2$

Here $\text{FAD}$ is undergoing reduction by a gain of two electrons and converted into ${\text{FADH}}_2$. Hence $\text{FAD}$ molecule acts as an oxidizing agent.

(d)

Interpretation Introduction

Interpretation: To classify each of the following molecules as (1) an oxidizing agent, (2) a reducing agent, or (3) neither an oxidizing agent nor a reducing agent.

a. NADH

b. ATP

c. FAD

d. CoA–SH

Concept introduction: The sum of various chemical reactions occurring in the human body is called metabolism and the reactions individually are known as metabolic reactions. During these metabolic reactions, the various metabolic intermediates are formed for the short time to complete the reactions.ATP,$\text{FAD}$,$\text{NADH}$ and CoA–SH are examples of a metabolic intermediate.

$\text{NADH}$ is the reduced form of nicotinamide adenine dinucleotide. It is employed asan oxidizing agent in various reactions like oxidation of secondary alcohol into a ketone. Its structure consists of three subunits: nicotinamide, ribose,and ADP.

ATP is a nucleotide which provides energy for the completion of various metabolic reactions occurring in our human body. The structure of ATP consists of adenine base, ribose sugar unit and the three phosphate groupconnected to each other by phosphoanhydride bonds.

Flavin adenine dinucleotideexists in two forms: oxidized form $\left(\text{FAD}\right)$ and reduced form $\left({\text{FADH}}_2\right)$. The main function of flavin adenine dinucleotide is to act as an oxidizing agent and used by the cell in oxidation reactions like oxidation of fatty acid.

Coenzyme A (CoA) is a coenzyme which is utilized in various metabolic reactions. The functions of coenzyme A include oxidation of pyruvate in the citric cycle and fatty acid oxidation.

Oxidizing agents are those species which gets reduced and oxidizes the other species present in the chemical reaction. Reducing agent is those species which gets oxidized and reduces the other species present in a chemical reaction. Generally, oxidizing agents are electron acceptor and reducing agents are electron donor.

Answer to Problem 23.44EP

Coenzyme A (CoA–SH) molecule is neither a reducing agent nor an oxidizing agent in metabolic reactions.

Explanation of Solution

Coenzyme A (CoA) is a coenzyme whose structure is based on the B vitamin pantothenic acid. Its structure consists of three subunits: 2-Aminoethanethiol, pantothenic acid, and phosphorylated ADP.

Coenzyme A is always in equilibrium with its acetyl form and therefore helps in transfer of acetyl group in metabolic reaction. The reaction for this change is

Here Coenzyme A (CoA) is not involved in electron transfer hence it is neithera reducing agent nor an oxidizing agent.

Conclusion

a. $\text{NADH}$ acts as a reducing agent in metabolic reactions.

b. ATP molecule is neither a reducing agent nor an oxidizing agent in metabolic reactions.

c. $\text{FAD}$ molecule acts as an oxidizing agent in metabolic reactions.

d. Coenzyme A (CoA–SH) molecule is neither a reducing agent nor an oxidizing agent in metabolic reactions.