Chapter 23, Problem 23.28E

Interpretation Introduction

(a)

Interpretation:

The total number of molecules of NADH that are obtained by one run through the citric acid cycle is to be stated.

Concept introduction:

The cycle which represents the set of chemical reactions that are utilized by all the aerobic or living organisms which helps them in releasing the stored amount of energy by the oxidation process of acetyl-CoA is known as citric acid cycle. This acetyl-CoA is obtained from the carbohydrates, protein and fats in the form of ATP.

Answer to Problem 23.28E

The total number of molecules of NADH that are obtained by one run through the citric acid cycle is three.

Explanation of Solution

The overall net equation that takes place in the citric acid cycle is given below.

$\begin{array}{l}\text{Acetyl}\text{CoA}+3{\text{NAD}}^{+}+\text{FAD}+\text{GDP}+{\text{P}}_i+2{\text{H}}_{\text{2}}\text{O}\to \\ 2{\text{CO}}_{\text{2}}+\text{CoA}-\text{S}-\text{H}+\text{3NADH}+{\text{2H}}^{+}+{\text{FADH}}_{\text{2}}+\text{GTP}\end{array}$

In the above equation, the requirement of oxidizing agent such as FAD and ${\text{NAD}}^{+}$ is fulfilled by the citric acid cycle. If these agents are not available then the overall reaction gets stopped.

In third step, the oxidation of isocitrate into $\text{α}-\text{ketoglutarate}$ takes place with the help of ${\text{NAD}}^{+}$ as shown below.

Figure 1

In this step, the reduction of ${\text{NAD}}^{+}$ takes place to form one $\text{NADH}$ molecule.

In fourth step, the oxidation of the mixture of CoA-S-H and $\text{α}-\text{ketoglutarate}$ into succinyl CoA takes place with the help of ${\text{NAD}}^{+}$ as shown below.

Figure 2

In this step, the reduction of ${\text{NAD}}^{+}$ takes place to form one $\text{NADH}$ molecule.

In eighth step, the oxidation of malate into oxaloacetate takes place with the help of ${\text{NAD}}^{+}$ as shown below.

Figure 3

In this step also, the reduction of ${\text{NAD}}^{+}$ takes place to form one $\text{NADH}$ molecule.

Therefore, the third, fourth and eighth steps of citric acid cycle give total three molecules of NADH.

Conclusion

The total number of molecules of NADH that are obtained by one run through the citric acid cycle has been stated above.

Interpretation Introduction

(b)

Interpretation:

The total number of molecules of ${\text{FADH}}_{\text{2}}$ that are obtained by one run through the citric acid cycle is to be stated.

Concept introduction:

The cycle which represents the set of chemical reactions that are utilized by all the aerobic or living organisms which helps them in releasing the stored amount of energy by the oxidation process of acetyl-CoA is known as citric acid cycle. This acetyl-CoA is obtained from the carbohydrates, protein and fats in the form of ATP.

Answer to Problem 23.28E

The total number of molecules of ${\text{FADH}}_{\text{2}}$ that are obtained by one run through the citric acid cycle is one.

Explanation of Solution

The sixth step of citric acid cycle includes the oxidation by FAD. In this step, the oxidation of succinate into fumarate takes place with the help of FAD as shown below.

Figure 4

In this step, the reduction of FAD (flavin adenine dinucleotide) takes place to form ${\text{FADH}}_{\text{2}}$. Therefore, the sixth step of citric acid cycle gives only one molecule of ${\text{FADH}}_{\text{2}}$.

Conclusion

The total number of molecules of ${\text{FADH}}_{\text{2}}$ that are obtained by one run through the citric acid cycle has been stated above.

Interpretation Introduction

(c)

Interpretation:

The total number of molecules of GTP that are obtained by one run through the citric acid cycle is to be stated.

Concept introduction:

The cycle which represents the set of chemical reactions that are utilized by all the aerobic or living organisms which helps them in releasing the stored amount of energy by the oxidation process of acetyl-CoA is known as citric acid cycle. This acetyl-CoA is obtained from the carbohydrates, protein and fats in the form of ATP.

Answer to Problem 23.28E

The total number of molecules GTP that are obtained by one run through the citric acid cycle is one.

Explanation of Solution

The fifth step of citric acid cycle includes the oxidation by GDP. In this step, the compound, succinyl CoA is converted into succinate with the help of GDP as shown below.

Figure 5

In this step, the GDP is also converted to one GTP molecule. Therefore, the fifth step of citric acid cycle gives only one molecule of GTP.

Conclusion

The total number of molecules of GTP that are obtained by one run through the citric acid cycle has been stated above.

Interpretation Introduction

(d)

Interpretation:

The total number of molecules of ${\text{CO}}_{\text{2}}$ that are obtained by one run through the citric acid cycle is to be stated.

Concept introduction:

The cycle which represents the set of chemical reactions that are utilized by all the aerobic or living organisms which helps them in releasing the stored amount of energy by the oxidation process of acetyl-CoA is known as citric acid cycle. This acetyl-CoA is obtained from the carbohydrates, protein and fats in the form of ATP.

Answer to Problem 23.28E

The total number of molecules ${\text{CO}}_{\text{2}}$ that are obtained by one run through the citric acid cycle is two.

Explanation of Solution

The overall net equation that takes place in the citric acid cycle is given below.

$\begin{array}{l}\text{Acetyl}\text{CoA}+3{\text{NAD}}^{+}+\text{FAD}+\text{GDP}+{\text{P}}_i+2{\text{H}}_{\text{2}}\text{O}\to \\ 2{\text{CO}}_{\text{2}}+\text{CoA}-\text{S}-\text{H}+\text{3NADH}+{\text{2H}}^{+}+{\text{FADH}}_{\text{2}}+\text{GTP}\end{array}$

According to the overall equation of citric acid cycle, total two molecules of ${\text{CO}}_{\text{2}}$ evolves during the third and fourth steps of the cycle as shown above.

Therefore, the third and fourth steps of citric acid cycle give two molecules of ${\text{CO}}_{\text{2}}$.

Conclusion

The total number of molecules of ${\text{CO}}_{\text{2}}$ that are obtained by one run through the citric acid cycle has been stated above.