Chapter 12, Problem 12.90EP

Indicate whether each of the following changes represents oxidation or reduction.

1. a. FADH₂ → FAD
2. b. FMN → FMNH₂
3. c. Fe(III)SP → Fe(II)SP
4. d. Cyt c₁ (Fe³⁺) → cyt c₁ (Fe²⁺)

Interpretation Introduction

Interpretation:

Whether the change ${\text{FADH}}_2\to \text{FAD}$ represents oxidation or reduction has to be indicated.

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:

Redox reactions involve oxidation and reduction reaction occurring simultaneously so that one species is oxidized and the other one is reduced. The species that gain hydrogen or electron is known as reduced form and the species that loss hydrogen or electron is known as oxidized form. The general representation of the redox reaction is,

  $\text{A}+{\text{H}}^{+}+{\text{e}}^{-}\to \text{AH}$

Here, A is oxidized form and AH is reduced form.

Answer to Problem 12.90EP

The change ${\text{FADH}}_2\to \text{FAD}$ represents oxidation as there is a loss of hydrogen in the reaction.

Explanation of Solution

In the complex II, electrons are transferred from the ${\text{FADH}}_{\text{2}}$ molecule produced in the citric acid cycle. FAD is the oxidized form and it gets reduced to form ${\text{FADH}}_{\text{2}}$. The reaction of the oxidation of ${\text{FADH}}_{\text{2}}$ is:

  ${\text{FADH}}_2\to \text{FAD}+2{\text{H}}^{+}+2{\text{e}}^{-}$

Here, ${\text{FADH}}_2$ lose hydrogen or electron and leads to the formation of FAD.

Interpretation Introduction

Interpretation:

Whether the change $\text{FMN}\to {\text{FMNH}}_2$ represents oxidation or reduction has to be indicated.

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:

Redox reactions involve oxidation and reduction reaction occurring simultaneously so that one species is oxidized and the other one is reduced. The species that gain hydrogen or electron is known as reduced form and the species that loss hydrogen or electron is known as oxidized form. The general representation of redox reaction is,

  $\text{A}+{\text{H}}^{+}+{\text{e}}^{-}\to \text{AH}$

Here, A is oxidized form and AH is reduced form.

Answer to Problem 12.90EP

The change $\text{FMN}\to {\text{FMNH}}_2$ represents reduction as there is a gain of hydrogen in the reaction.

Explanation of Solution

Flavin mononucleotide is the structural component of the complex I of the electron transport chain. Flavin mononucleotide exists in two forms: FMN (oxidized form) and ${\text{FMNH}}_2$(reduced form). The redox reaction for this change is:

  $\text{FMN}+{\text{2H}}^{+}+2{\text{e}}^{-}\stackrel{\text{Reduction}}{\to }{\text{FMNH}}_2$

Here, FMN gains electrons and hydrogen and leads to the formation of ${\text{FMNH}}_2$.

Interpretation Introduction

Interpretation:

Whether the change $\text{Fe}\left(\text{III}\right)\text{SP}\to \text{Fe}\left(\text{II}\right)\text{SP}$ represents oxidation or reduction has to be indicated.

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:

Redox reactions involve oxidation and reduction reaction occurring simultaneously so that one species is oxidized and the other one is reduced. The species that gain hydrogen or electron is known as reduced form and the species that loss hydrogen or electron is known as oxidized form. The general representation of redox reaction is,

  $\text{A}+{\text{H}}^{+}+{\text{e}}^{-}\to \text{AH}$

Here, A is oxidized form and AH is reduced form.

Answer to Problem 12.90EP

The change $\text{Fe}\left(\text{III}\right)\text{SP}\to \text{Fe}\left(\text{II}\right)\text{SP}$ represents reduction as there is a gain of an electron in the reaction.

Explanation of Solution

Iron-sulfur proteins $\left(\text{FeSP}\right)$ are a structural component of the complex I and consist of iron that changes its oxidation state from $+3$ to $+2$ in the complex. Iron in $\text{Fe}\left(\text{III}\right)\text{SP}$ undergoes reduction and leads to the formation of $\text{Fe}\left(\text{II}\right)\text{SP}$. The reaction to this change is:

  $\text{Fe}\left(\text{III}\right)\text{SP}+2{\text{e}}^{-}\stackrel{\text{Reduction}}{\to }\text{Fe}\left(\text{II}\right)\text{SP}$

Interpretation Introduction

Interpretation:

To indicate whether the change $\text{cyt}{\text{c}}_{\text{1}}\left({\text{Fe}}^{3+}\right)\to \text{cyt}{\text{c}}_{\text{1}}\left({\text{Fe}}^{2+}\right)$ represents oxidation or reduction.

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:

Redox reactions involve oxidation and reduction reaction occurring simultaneously so that one species is oxidized and the other one is reduced. The species that gain hydrogen or electron is known as reduced form and the species that loss hydrogen or electron is known as oxidized form. The general representation of redox reaction is,

  $\text{A}+{\text{H}}^{+}+{\text{e}}^{-}\to \text{AH}$

Here, A is oxidized form and AH is reduced form.

Answer to Problem 12.90EP

The change $\text{cyt}{\text{c}}_{\text{1}}\left({\text{Fe}}^{3+}\right)\to \text{cyt}{\text{c}}_{\text{1}}\left({\text{Fe}}^{2+}\right)$ represents reduction as there is a gain of an electron in the reaction.

Explanation of Solution

Cytochromes are a structural component of the complex III and consist of iron that changes its oxidation state from $+2$ to $+3$ or vice-versa in the complex. Iron in $\text{cyt}{\text{c}}_1\left({\text{Fe}}^{3+}\right)$ undergoes reduction and leads to the formation of $\text{cyt}{\text{c}}_1\left({\text{Fe}}^{2+}\right)$. The reaction to this change is:

  $\text{cyt}{\text{c}}_{\text{1}}\left({\text{Fe}}^{3+}\right)+{\text{e}}^{-}\stackrel{\text{Reduction}}{\to }\text{cyt}{\text{c}}_{\text{1}}\left({\text{Fe}}^{2+}\right)$