Chapter 12, Problem 12.92EP

(a)

Interpretation Introduction

Interpretation: To determine the electron carrier FADH₂ is associated with which of the protein complexes (I, II, III, and IV) of the ETC.

Concept introduction: Electron transport chain is a sequence of biochemical reactions in which electrons and hydrogen atoms from the citric acid cycle are transferred to various intermediate carriers and finally reacts with molecular oxygen to form a water molecule. There are four complexes associated with the electron transport chain that is present in the inner mitochondrial membrane. The four complexes that help in the electron transfer in the electron transport chain are:

Complex I: $\text{NADH-coenzyme}\text{Q reductase}$

Complex II: $\text{Succinate-coenzyme}\text{Q reductase}$

Complex III: $\text{Coenzyme}\text{Q-cytochrome c reductase}$

Complex IV: $\text{Cytochrome c oxidase}$

An overview of the electron transport chain is as follows:

Answer to Problem 12.92EP

FADH₂ is associated with the complex II of the electron transport chain. Electrons from the citric acid cycle are transported to complex II through FADH₂ molecule.

Explanation of Solution

Complex II consists of four subunits in its structure. This complex interacts initially with the electrons that are coming after the reduction of FADH₂. FADH₂ produced in the citric acid cycle transfers the electron to the complex II. The diagrammatic representation of electron transfer in complex II in the electron transfer chain is:

(b)

Interpretation Introduction

Interpretation: To determine that the electron carrier $\text{FeSP}$ is associated with which of the protein complexes (I, II, III, and IV) of the ETC.

Concept introduction: Electron transport chain is a sequence of biochemical reactions in which electrons and hydrogen atoms from the citric acid cycle are transferred to various intermediate carriers and finally reacts with molecular oxygen to form a water molecule. There are four complexes associated with the electron transport chain that is present in the inner mitochondrial membrane. The four complexes that help in the electron transfer in the electron transport chain are:

Complex I: $\text{NADH-coenzyme}\text{Q reductase}$

Complex II: $\text{Succinate-coenzyme}\text{Q reductase}$

Complex III: $\text{Coenzyme}\text{Q-cytochrome c reductase}$

Complex IV: $\text{Cytochrome c oxidase}$

An overview of the electron transport chain is as follows:

Answer to Problem 12.92EP

$\text{FeSP}$ is associated with complex I, complex II and complex III of the electron transport chain. $\text{FeSP}$ is present as the structural component in the complex II, III and IV. Iron-sulfur protein has iron in its structure that can change its oxidation state from $+2$ to $+3$.

Explanation of Solution

Iron-sulfur protein $\left(\text{FeSP}\right)$ is present as the structural component in the complex II, III and IV.

Complex I consists of more than 40 structural subunits. Its structure has B-vitamin-containing flavin mononucleotide $\left(\text{FMN}\right)$ and various iron-sulfur proteins $\left(\text{FeSP}\right)$.

The diagrammatic representation of electron transfer in complex I in the electron transfer chain is as follows:

Complex II consists of four subunits in its structure. This complex interacts initially with the electrons that are coming after the reduction of FADH₂. FADH₂ produced in the citric acid cycle transfers the electron to the complex II. The diagrammatic representation of electron transfer in complex II in the electron transfer chain is:

Complex III consists of 11 structural subunits. Its structural subunits contain iron-sulfur proteins and various cytochromes. $\text{cyt b}$ and ${\text{cyt c}}_1$ are present in the complex III. ${\text{CoQH}}_{\text{2}}$ from complex I and complex II transfers electrons to complex III and start the reactions of complex III. The diagrammatic representation of electron transfer in complex I in the electron transfer chain is as follows:

(c)

Interpretation Introduction

Interpretation: To determine that the electron carrier $\text{cyt c}$ is associated with which of the protein complexes (I, II, III, and IV) of the ETC.

Concept introduction: Electron transport chain is a sequence of biochemical reactions in which electrons and hydrogen atoms from the citric acid cycle are transferred to various intermediate carriers and finally reacts with molecular oxygen to form a water molecule. There are four complexes associated with the electron transport chain that is present in the inner mitochondrial membrane. The four complexes that help in the electron transfer in the electron transport chain are:

Complex I: $\text{NADH-coenzyme}\text{Q reductase}$

Complex II: $\text{Succinate-coenzyme}\text{Q reductase}$

Complex III: $\text{Coenzyme}\text{Q-cytochrome c reductase}$

Complex IV: $\text{Cytochrome c oxidase}$

An overview of the electron transport chain is as follows:

Answer to Problem 12.92EP

$\text{Cyt c}$ is associated with complex III and complex IV of the electron transport chain. $\text{Cyt c}$ acts as a mobile electron carrier from complex III to complex IV.

Explanation of Solution

Electrons are transferred from the complex III to complex IV by $\text{cyt}\text{c}$.

Complex IV contains 13 structural subunits. It has two cytochrome units that have copper along with iron. The copper also participates in the redox reactions and changes its oxidation state from $+2$ to $+1$. In the complex IV, $\text{cyt}\text{c}$ transfers electrons to $\text{cyt}\text{a}$ and $\text{cyt}\text{a}$ transfers it to $\text{cyt}{\text{a}}_3$. In the last step, electrons from $\text{cyt}{\text{a}}_3$ and hydrogen ions react with molecular oxygen to form water. The diagrammatic representation of the electron transfer in complex IV in the electron transport chain is:

(d)

Interpretation Introduction

Interpretation: To determine that the electron carrier ${\text{cyt c}}_1$ is associated with which of the protein complexes (I, II, III, and IV) of the ETC.

Concept introduction: Electron transport chain is a sequence of biochemical reactions in which electrons and hydrogen atoms from the citric acid cycle are transferred to various intermediate carriers and finally reacts with molecular oxygen to form a water molecule. There are four complexes associated with the electron transport chain that is present in the inner mitochondrial membrane. The four complexes that help in the electron transfer in the electron transport chain are:

Complex I: $\text{NADH-coenzyme}\text{Q reductase}$

Complex II: $\text{Succinate-coenzyme}\text{Q reductase}$

Complex III: $\text{Coenzyme}\text{Q-cytochrome c reductase}$

Complex IV: $\text{Cytochrome c oxidase}$

An overview of the electron transport chain is as follows:

Answer to Problem 12.92EP

${\text{Cyt c}}_1$ is associated with the complex III of the electron transport chain. ${\text{Cyt c}}_1$ transfers an electron to $\text{FeSP}$ unit in the complex III.

Explanation of Solution

Complex III consists of 11 structural subunits. Its structural subunits contain iron-sulfur proteins and various cytochromes. $\text{cyt b}$ and ${\text{cyt c}}_1$ are present in the complex III. Initially, ${\text{CoQH}}_{\text{2}}$ is oxidized and releases two electrons that are transferred to $\text{FeSP}$ and then to $\text{cyt b}$. The electrons from $\text{cyt b}$ is then again transferred to another unit of $\text{FeSP}$ and then to ${\text{cyt c}}_1$. ${\text{Cyt c}}_1$ transfers it to $\text{cyt c}$ unit and finally, electrons are transferred from complex III to complex IV through $\text{cyt c}$. The diagrammatic representation of electron transfer in complex I in the electron transfer chain is as follows: