Chapter 24, Problem 24.117EP

(a)

Interpretation Introduction

Interpretation: To indicate whether B vitamin thiamin is involved in (1) glycolysis, (2) gluconeogenesis, (3) lactate fermentation, or (4) glycogenolysis as a cofactor.

Concept introduction: Vitamins are defined as the micronutrients that are needed in a small amount for the proper functioning of the metabolic activities in the organisms.

Cofactors are non-protein organic compounds that are used along with the enzymes and help to carry forward the reaction. Cofactors cannot perform on their own alone.

In the glycolysis metabolic pathway, a glucose molecule breaks down into two pyruvate molecules. In gluconeogenesis process, glucose is produced from non-carbohydrate substances. Glycogenolysis is the metabolic pathway that converts glycogen to $\text{glucose 6}-\text{phosphate}$.

In the absence of oxygen, pyruvate is converted to lactate by lactate dehydrogenase enzymes in the human body. In this reaction, NADH is oxidized to ${\text{NAD}}^{+}$. This anaerobic reduction is called lactate fermentation.

Niacin $\left({\text{as NADH, NAD}}^{+}\right)$ , thiamin (as TPP), riboflavin (as FAD),  pantothenic acid $\left(\text{as CoA}\right)$, biotin, and ${\text{vitamin B}}_6$ (as PLP) are the different B vitamins involved in the reactions associated with the metabolism of carbohydrates.

Answer to Problem 24.117EP

None of the given processes includes B vitamin thiamin as a cofactor. B vitamin thiamin is needed as a cofactor in the conversion of pyruvate to $\text{acetyl CoA}$.

Explanation of Solution

B vitamin thiamin is encountered in the form of thiamin pyrophosphate (TPP) in the carbohydrate metabolism. TPP in not involved in glycolysis, gluconeogenesis, lactate fermentation, and glycogenolysis. Hence, none of the given processes includes vitamin thiamin as a cofactor.

Pyruvate is converted to $\text{acetyl CoA}$ under oxygen-rich conditions by pyruvate dehydrogenase complex enzymes in the human body. The chemical reaction for the formation of $\text{acetyl CoA}$ is as follows:

Pyruvate dehydrogenase complex contains three different enzymes. Each enzyme contains numerous subunits. The overall reaction requires FAD, $\text{CoA}-\text{SH}$, ${\text{NAD}}^{+}$, lipoic acid, and thiamin pyrophosphate (TPP). Therefore, TPP B-vitamin-containing coenzyme is needed in the conversion of pyruvate to $\text{acetyl CoA}$.

(b)

Interpretation Introduction

Interpretation: To indicate B vitamin riboflavin is involved in (1) glycolysis, (2) gluconeogenesis, (3) lactate fermentation, or (4) glycogenolysis as a cofactor.

Concept introduction: Vitamins are defined as the micronutrients that are needed in a small amount for the proper functioning of the metabolic activities in the organisms.

Cofactors are non-protein organic compounds that are used along with the enzymes and help to carry forward the reaction. Cofactors cannot perform on their own alone.

In the glycolysis metabolic pathway, a glucose molecule breaks down into two pyruvate molecules. In gluconeogenesis process, glucose is produced from non-carbohydrate substances. Glycogenolysis is the metabolic pathway that converts glycogen to $\text{glucose 6}-\text{phosphate}$.

In the absence of oxygen, pyruvate is converted to lactate by lactate dehydrogenase enzymes in the human body. In this reaction, NADH is oxidized to ${\text{NAD}}^{+}$. This anaerobic reduction is called lactate fermentation.

Niacin $\left({\text{as NADH, NAD}}^{+}\right)$ , thiamin (as TPP), riboflavin (as FAD),  pantothenic acid $\left(\text{as CoA}\right)$, biotin, and ${\text{vitamin B}}_6$ (as PLP) are the different B vitamins involved in the reactions associated with the metabolism of carbohydrates.

Answer to Problem 24.117EP

None of the given processes includes vitamin riboflavin as a cofactor. B vitamin riboflavin is needed as a cofactor in the citric acid cycle.

Explanation of Solution

B vitamin riboflavin is encountered in the form of FAD(Flavin adenine dinucleotide) in the carbohydrate metabolism. FAD in not involved in glycolysis, gluconeogenesis, lactate fermentation, and glycogenolysis. Hence, none of the given processes includes B vitamin riboflavin as a cofactor.

The citric acid cycle is the third stage of the biochemical energy production process. The cycle includes the reactions in which the acetyl part of acetyl CoA is oxidized and leads to the formation of carbon dioxide and $\text{CoA}-\text{SH}$. The net overall equation for the citric acid cycle is as follows:

$\begin{array}{c}\text{Acetyl CoA}+{\text{3NAD}}^{+}+\text{FAD}+\text{GDP}+{\text{HPO}}_4^{2-}\left({\text{P}}_{\text{i}}\right)+2{\text{H}}_2\text{O}\to {\text{2CO}}_2+\text{CoA}-\text{SH}+3\text{NADH}\\ +3{\text{H}}^{+}+{\text{FADH}}_2+\text{GTP}\end{array}$

(c)

Interpretation Introduction

Interpretation: To indicate whether B vitamin pantothenic acid is involved in (1) glycolysis, (2) gluconeogenesis, (3) lactate fermentation, or (4) glycogenolysis as a cofactor.

Concept introduction: Vitamins are defined as the micronutrients that are needed in a small amount for the proper functioning of the metabolic activities in the organisms.

Cofactors are non-protein organic compounds that are used along with the enzymes and help to carry forward the reaction. Cofactors cannot perform on their own alone.

In the glycolysis metabolic pathway, a glucose molecule breaks down into two pyruvate molecules. In gluconeogenesis process, glucose is produced from non-carbohydrate substances. Glycogenolysis is the metabolic pathway that converts glycogen to $\text{glucose 6}-\text{phosphate}$.

In the absence of oxygen, pyruvate is converted to lactate by lactate dehydrogenase enzymes in the human body. In this reaction, NADH is oxidized to ${\text{NAD}}^{+}$. This anaerobic reduction is called lactate fermentation.

Niacin $\left({\text{as NADH, NAD}}^{+}\right)$ , thiamin (as TPP), riboflavin (as FAD),  pantothenic acid $\left(\text{as CoA}\right)$, biotin, and ${\text{vitamin B}}_6$ (as PLP) are the different B vitamins involved in the reactions associated with the metabolism of carbohydrates.

Answer to Problem 24.117EP

None of the given processes includes B vitamin pantothenic acid as a cofactor. B vitamin pantothenic acid is needed as a cofactor in the conversion of pyruvate to $\text{acetyl CoA}$.

Explanation of Solution

B vitamin pantothenic acid is encountered in the form of $\text{CoA}\left(\text{coenzyme A}\right)$ in the carbohydrate metabolism. $\text{CoA}$ is not involved in glycolysis, gluconeogenesis, lactate fermentation, and glycogenolysis. Hence, none of the given processes includes B vitamin pantothenic acid as a cofactor.

Pyruvate is converted to $\text{acetyl CoA}$ under oxygen-rich conditions by pyruvate dehydrogenase complex enzymes in the human body. The chemical reaction for the formation of $\text{acetyl CoA}$ is as follows:

Pyruvate dehydrogenase complex contains three different enzymes. Each enzyme contains numerous subunits. The overall reaction requires FAD, $\text{CoA}-\text{SH}$, ${\text{NAD}}^{+}$, lipoic acid, and thiamin pyrophosphate (TPP). Since $\text{CoA}-\text{SH}$ is needed, therefore, B vitamin pantothenic acid is needed as a cofactor in the conversion of pyruvate to $\text{acetyl CoA}$.

Interpretation Introduction

(d)

Interpretation: To indicate ${\text{vitamin B}}_6$ is involved in (1) glycolysis, (2) gluconeogenesis, (3) lactate fermentation, or (4) glycogenolysis as a cofactor.

Concept introduction: Vitamins are defined as the micronutrients that are needed in a small amount for the proper functioning of the metabolic activities in the organisms.

Cofactors are non-protein organic compounds that are used along with the enzymes and help to carry forward the reaction. Cofactors cannot perform on their own alone.

In the glycolysis metabolic pathway, a glucose molecule breaks down into two pyruvate molecules. In gluconeogenesis process, glucose is produced from non-carbohydrate substances. Glycogenolysis is the metabolic pathway that converts glycogen to $\text{glucose 6}-\text{phosphate}$.

In the absence of oxygen, pyruvate is converted to lactate by lactate dehydrogenase enzymes in the human body. In this reaction, NADH is oxidized to ${\text{NAD}}^{+}$. This anaerobic reduction is called lactate fermentation.

Niacin $\left({\text{as NADH, NAD}}^{+}\right)$ , thiamin (as TPP), riboflavin (as FAD),  pantothenic acid $\left(\text{as CoA}\right)$, biotin, and ${\text{vitamin B}}_6$ (as PLP) are the different B vitamins involved in the reactions associated with the metabolism of carbohydrates.

Answer to Problem 24.117EP

${\text{Vitamin B}}_6$, in the form of PLP, is involved in glycogenolysis.

Explanation of Solution

${\text{Vitamin B}}_6$ is encountered in the form of $\text{PLP}\left(\text{pyridoxial}-5^{\text{'}}-\text{phosphate}\right)$ in the carbohydrate metabolism. PLP is involved in glycogenolysis. An overview of glycogenolysis metabolic pathway is as follows: