Chapter 23, Problem 23.86EP

(a)

Interpretation Introduction

Interpretation: To identify whether the list of the electron carrier $\text{FeSP}$, $\text{CoQ}$ and $\text{FMN}$ 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 23.86EP

No, the given order for electron carriers $\text{FeSP}$, $\text{CoQ}$ and $\text{FMN}$ are in the order as they are encountered in the electron transport chain.

Explanation of Solution

In the complex, I initially, $\text{NADH}$ 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 and then $\text{FeSP}$ followed by $\text{CoQ}$. Therefore, the given order of the electron carriers is incorrect.

(b)

Interpretation Introduction

Interpretation: To identify whether the list of the electron carrier $\text{cyt}\text{b}$, $\text{cyt}\text{c}$ 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 23.86EP

Yes, the given order for electron carriers $\text{cyt}\text{b}$, $\text{cyt}\text{c}$ and $\text{cyt}\text{a}$ 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 $\text{coenzyme Q}\left({\text{CoQH}}_{\text{2}}\right)$. Electrons are transferred from complex III to complex IV. In the complex IV, the formation of water takes place.

$\text{Cyt}\text{b}$ is encountered in the complex III and $\text{cyt}\text{c}$ carries the electrons from the complex III to complex IV. $\text{Cyt}\text{a}$ is used to transfer electron in complex IV. $\text{Cyt}\text{a}$ has copper along with iron that can also participate in a redox reaction. $\text{Cyt}\text{b}$ is encountered first in the electron transport chain then $\text{cyt}\text{c}$ followed by $\text{cyt}\text{a}$. Therefore, the given order of the electron carriers is correct.

(c)

Interpretation Introduction

Interpretation: To identify whether the list of the electron carrier $\text{NADH}$, ${\text{FADH}}_2$, and $\text{cyt}\text{c}$ 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 23.86EP

Yes, the given order for electron carriers $\text{NADH}$, ${\text{FADH}}_2$ and $\text{cyt}\text{c}$ are 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. $\text{Cyt}\text{c}$ transfers the electrons from complex III to complex IV. $\text{NADH}$ is encountered first in the electron transport chain then ${\text{FADH}}_2$ followed by $\text{cyt}\text{c}$. Therefore, the given order of the electron carriers is correct.

(d)

Interpretation Introduction

Interpretation: To identify whether the list of the electron carrier $\text{FMN}$, $\text{FeSP}$, 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 23.86EP

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

Explanation of Solution

In complex, I initially, $\text{NADH}$ 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 and then $\text{FeSP}$ followed by $\text{CoQ}$. Therefore, the given order of the electron carriers is correct.