Chapter 23, Problem 23.85EP

(a)

Interpretation Introduction

Interpretation: To identify whether the list of the electron carrier $\text{FeSP}$, $\text{CoQ}$ and $\text{cyt}\text{b}$ is in the order they are encountered in the electron transport chain or not.

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 23.85EP

Yes, the given order for electron carriers $\text{FeSP}$, $\text{CoQ}$ and $\text{cyt}\text{b}$ are in the order as they are encountered in the electron transport chain.

Explanation of Solution

In the electron transport chain, electrons are transferred from complex I and II to complex III through $\text{coenzyme Q}\left({\text{CoQH}}_{\text{2}}\right)$. $\text{FeSP}$ is a structural component of the complex I and $\text{CoQ}$ is encountered in the complex II. $\text{Cyt}\text{b}$ is present in the complex III and transfers an electron to the iron-sulfur proteins. $\text{FeSP}$ is encountered first in the electron transport chain then $\text{CoQ}$ followed by $\text{cyt}\text{b}$. Therefore, the given order of the electron carriers is correct.

(b)

Interpretation Introduction

Interpretation: To identify whether the list of the electron carrier $\text{FMN}$, $\text{cyt}\text{c}$ and $\text{CoQ}$ is in the order they are encountered in the electron transport chain or not.

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 23.85EP

No, the given order for electron carriers $\text{FMN}$, $\text{cyt}\text{c}$ and $\text{CoQ}$ are not in the order as they are encountered in the electron transport chain.

Explanation of Solution

In the electron transport chain, electrons are transferred from complex I and II to complex III through $\text{coenzyme Q}\left({\text{CoQH}}_{\text{2}}\right)$. $\text{FMN}$ is a structural component of the complex I and $\text{CoQ}$ is encountered in the complex I and II. $\text{Cyt}\text{c}$ carries the electron from complex III to complex IV and has iron in its structure that can change its oxidation state from $+2$ to $+3$. $\text{FMN}$ is encountered first in the electron transport chain then $\text{CoQ}$ followed by $\text{cyt}\text{c}$. Therefore, the given order of the electron carriers is incorrect.

(c)

Interpretation Introduction

Interpretation: To identify whether the list of the electron carrier $\text{CoQ}$, $\text{FMN}$ and $\text{cyt}\text{a}$ is in the order they are encountered in the electron transport chain or not.

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 23.85EP

No, the given order for electron carriers $\text{CoQ}$, $\text{FMN}$ and $\text{cyt}\text{a}$ are not in the order as they are encountered in the electron transport chain.

Explanation of Solution

In the complex I initially, NADH is oxidized and releases two electrons that reduce $\text{FMN}$ molecule present in the complex I to ${\text{FMNH}}_2$ molecule. Then again ${\text{FMNH}}_2$ is oxidized to regenerate $\text{FMN}$ molecule. The electrons released after the oxidation are utilized to reduce $\text{2Fe}\left(\text{III}\right)\text{SP}$. The reduced form $\text{2Fe}\left(\text{II}\right)\text{SP}$ is again oxidized to regenerate $\text{2Fe}\left(\text{III}\right)\text{SP}$. The electrons released after the oxidation are utilized to reduce $\text{CoQ}$.

$\text{FMN}$ is encountered first in the complex I. It is involved in the redox reaction and the iron present in it changes its oxidation state from $+2$ to $+3$. $\text{CoQ}$ is encountered in the last reaction of complex I and II. $\text{CoQ}$ is reduced to ${\text{CoQH}}_{\text{2}}$ and transfers electrons to complex III. $\text{cyt}\text{a}$ is encountered in the complex IV. Therefore, the given order of the electron carriers is incorrect.

(d)

Interpretation Introduction

Interpretation: To identify whether the list of the electron carrierFADH₂, NADH and $\text{FeSP}$ is in the order they are encountered in the electron transport chain or not.

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 23.85EP

No, the given order for electron carriers ${\text{FADH}}_{\text{2}}$, $\text{NADH}$ and $\text{FeSP}$ are not in the order as they are encountered in the electron transport chain.

Explanation of Solution

In complex I, electrons are transferred from the $\text{NADH}$ molecule produced in the citric acid cycle. Initially $\text{NADH}$ interacts with complex I and gets oxidized. On the other hand in the complex II, electrons are transferred from the ${\text{FADH}}_{\text{2}}$ molecule produced in the citric acid cycle. Initially ${\text{FADH}}_{\text{2}}$ interacts with complex II and gets oxidized. $\text{FeSP}$ is a structural component of the complex I.

$\text{NADH}$ is encountered in the complex I and ${\text{FADH}}_{\text{2}}$ is encountered in the complex II. Therefore, the given order of the electron carriers is incorrect.