ETS Questions in English

(C) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain $(ETC)$.
In photosynthesis, cytochromes (like $Cytochrome \, b_6f$) are present in the thylakoid membrane to facilitate electron flow.
In cellular respiration, cytochromes (like $Cytochrome \, c$, $a$, and $a_3$) are essential components of the inner mitochondrial membrane for oxidative phosphorylation.
Therefore, cytochromes are required in both processes.

(A) The electron transport system $(ETS)$ or electron transport chain $(ETC)$ is a series of protein complexes and electron carriers located in the $Inner \text{ } mitochondrial \text{ } membrane$.
These complexes facilitate the transfer of electrons from $NADH$ and $FADH_2$ to oxygen, which is the final electron acceptor.
This process creates a proton gradient across the inner mitochondrial membrane, which drives the synthesis of $ATP$ via $ATP \text{ } synthase$.

(A) In one turn of the Krebs cycle ($TCA$ cycle), the following reduced coenzymes are produced:
$1$. $3$ molecules of $NADH + H^+$
$2$. $1$ molecule of $FADH_2$
$3$. $1$ molecule of $GTP$ (which is equivalent to $1$ $ATP$)
During the electron transport system $(ETS)$:
- Each $NADH + H^+$ produces $3$ $ATP$ molecules.
- Each $FADH_2$ produces $2$ $ATP$ molecules.
Calculation:
- $3$ $NADH \times 3 = 9$ $ATP$
- $1$ $FADH_2 \times 2 = 2$ $ATP$
- Total $ATP$ from $ETS$ = $9 + 2 = 11$ $ATP$.
Therefore, the number of $ATP$ molecules produced through the electron transport system from the intermediates of a single turn of the Krebs cycle is $11$.

(C) The electron transport chain $(ETC)$ is located in the inner mitochondrial membrane.
During the final step of the $ETC$,the enzyme complex $IV$ (also known as cytochrome $c$ oxidase) is responsible for the transfer of electrons.
This complex contains cytochromes $a$ and $a_3$,along with two copper centers.
Cytochrome $a_3$ is the specific component that donates electrons directly to molecular oxygen $(O_2)$,which then combines with protons $(H^+)$ to form water $(H_2O)$.

(A) In the electron transport system $(ETS)$ located in the inner mitochondrial membrane,electrons are transferred through a series of complexes.
Specifically,the sequence of cytochromes involved in the electron transport chain is $cyt. b \rightarrow cyt. c_1 \rightarrow cyt. c \rightarrow cyt. a \rightarrow cyt. a_3$.
Therefore,the correct sequence among the given options is $cyt. b, c, a, a_3$.

(D) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport system $(ETS)$.
They are located in the inner mitochondrial membrane and play a crucial role in the process of cellular respiration by facilitating the transfer of electrons to oxygen,which leads to the synthesis of $ATP$ via oxidative phosphorylation.

(A) The chemiosmotic theory,proposed by Peter Mitchell,explains that $ATP$ synthesis is driven by the flow of protons ($H^+$ ions) across a membrane.
In mitochondria,the electron transport chain pumps protons from the matrix into the intermembrane space,creating a proton gradient (electrochemical gradient) across the inner mitochondrial membrane.
This gradient represents stored potential energy.
Protons flow back into the matrix through the $ATP$ synthase enzyme complex.
This flow of protons provides the energy required for the phosphorylation of $ADP$ to form $ATP$.

(A) In aerobic respiration,the Electron Transport System $(ETS)$ is located in the inner mitochondrial membrane.
During the process of oxidative phosphorylation,electrons are passed through a series of carriers.
At the end of the chain,the final electron acceptor is molecular oxygen $(O_2)$.
Oxygen combines with electrons and protons $(H^+)$ to form water $(H_2O)$,which is a crucial step for the continuation of the electron transport chain and the production of $ATP$.

(C) In the $ETS$ (Electron Transport System) located in the inner mitochondrial membrane,electrons are passed through a series of complexes.
At the end of this chain,the final electron acceptor is $O_2$ (Oxygen).
Oxygen accepts the electrons and combines with protons $(H^+)$ to form water $(H_2O)$,which is a crucial step in aerobic respiration.

(B) The complete oxidation of glucose involves glycolysis,the link reaction,the Krebs cycle,and the Electron Transport System $(ETS)$.
Glycolysis produces a net gain of $2$ $ATP$ molecules.
The Krebs cycle produces $2$ $ATP$ (or $GTP$) molecules per glucose molecule.
The Electron Transport System $(ETS)$ is the final stage where the majority of $ATP$ is synthesized through oxidative phosphorylation.
In the $ETS$,the reduced coenzymes ($NADH$ and $FADH_2$) generated in earlier stages donate electrons,creating a proton gradient that drives $ATP$ synthase to produce approximately $28$ to $30$ $ATP$ molecules.
Therefore,the maximum number of $ATP$ molecules is formed during the Electron Transport System $(ETS)$.

(D) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain $(ETC)$.
In photosynthesis, cytochromes (like $Cyt \, b_6f$) are essential components of the photosynthetic electron transport chain in the thylakoid membrane.
In respiration, cytochromes (like $Cyt \, b, c_1, c, a, a_3$) are vital components of the mitochondrial electron transport system, which facilitates the production of $ATP$ through oxidative phosphorylation.
Therefore, cytochromes are required for both respiration and photosynthesis.

(B) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain $(ETC)$ during cellular respiration and photosynthesis.
These proteins contain a heme group,which is an iron-porphyrin complex.
Phytochrome is a pigment protein involved in light sensing in plants but does not contain an iron-porphyrin complex.
Chlorophyll contains a magnesium-porphyrin complex,not an iron-porphyrin complex.

(C) In the Electron Transport System $(ETS)$,the components are arranged in a specific sequence to facilitate the transfer of electrons. For the transfer of $2$ $e^-$ (which corresponds to the oxidation of one molecule of $NADH$ or $FADH_2$),each cytochrome molecule acts as a carrier in a $1:1$ ratio. Therefore,for the transfer of $2$ $e^-$,only $1$ molecule of each cytochrome is required to participate in the chain.

(B) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain.
Cytochrome $a$ contains a heme group,which is an $Fe$ porphyrin ring structure.
Unlike chlorophyll,which contains a magnesium $(Mg)$ porphyrin ring,cytochromes utilize iron $(Fe)$ as the central metal ion within the porphyrin structure to facilitate redox reactions.

(A) In the electron transport system $(ETS)$ located in the inner mitochondrial membrane,electrons are transferred through a series of carriers.
The sequence of electron transport is as follows: $NADH \rightarrow$ Complex $I \rightarrow$ Ubiquinone $\rightarrow$ Complex $III$ $(cyt\ b, cyt\ c_1, cyt\ c)$ $\rightarrow$ Complex $IV$ $(cyt\ a, cyt\ a_3)$ $\rightarrow$ $O_2$.
Among the given options,the sequence $cyt\ b, c, a, a_3$ represents the correct order of electron flow through the cytochromes in the electron transport chain.

(A) Oxidative phosphorylation is the process in which $ATP$ is formed as a result of the transfer of electrons from $NADH$ or $FADH_2$ to $O_2$ by a series of electron carriers. This process takes place in the inner mitochondrial membrane of the mitochondria. Therefore,the correct option is $A$.

(C) During oxidative phosphorylation,the electron transport system $(ETS)$ creates a proton gradient across the inner mitochondrial membrane.
Protons $(H^+)$ accumulate in the intermembrane space (also known as the perimitochondrial space or $PMS$),creating a high concentration compared to the mitochondrial matrix.
The movement of protons back into the matrix through the $F_0-F_1$ particle ($ATP$ synthase) is called proton efflux.
This flow of protons down their electrochemical gradient provides the necessary energy to drive the phosphorylation of $ADP$ to $ATP$.

(B) In cellular respiration,the process of aerobic respiration involves glycolysis,the Krebs cycle,and the Electron Transport System $(ETS)$.
Glycolysis occurs in the cytoplasm and produces a small amount of $ATP$.
The Krebs cycle occurs in the mitochondrial matrix and produces some $ATP$/$GTP$ along with electron carriers ($NADH$ and $FADH_2$).
The Electron Transport System $(ETS)$ and oxidative phosphorylation,which occur in the inner mitochondrial membrane,utilize these electron carriers to produce the maximum amount of $ATP$.
Since the Krebs cycle is the primary metabolic pathway that generates the majority of the reduced coenzymes ($NADH$ and $FADH_2$) required for the massive $ATP$ production in the $ETS$,it is often considered the stage where the energy-yielding potential is maximized compared to glycolysis or anaerobic processes.

(B) During the Electron Transport System $(ETS)$,$FADH_2$ is oxidized at Complex-$II$ (succinate dehydrogenase).
Electrons from $FADH_2$ are transferred to ubiquinone,bypassing Complex-$I$.
As these electrons pass through Complex-$III$ and Complex-$IV$,protons are pumped into the intermembrane space.
The oxidation of one molecule of $FADH_2$ results in the synthesis of $2$ $ATP$ molecules via oxidative phosphorylation.

(A) Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients,thereby releasing energy which is used to produce $ATP$.
This process takes place in the inner mitochondrial membrane of the mitochondria.
During this process,electrons are transferred from electron donors to electron acceptors such as oxygen,in redox reactions.
These redox reactions release energy,which is used to form $ATP$.

(C) During cellular respiration,the electron transport system $(ETS)$ occurs in the inner mitochondrial membrane.
Here,electrons and protons $(H^+)$ released from $NADH$ and $FADH_2$ are passed through various carriers.
At the end of the electron transport chain,these electrons and protons combine with molecular oxygen $(O_2)$.
Thus,$O_2$ acts as the final electron and $H_2$ acceptor to form water $(H_2O)$.

(B) In the electron transport system $(ETS)$ located in the inner mitochondrial membrane,the final step involves the transfer of electrons to oxygen.
Complex $IV$ (Cytochrome $c$ oxidase complex) contains cytochromes $a$ and $a_3$,along with two copper centers.
Cytochrome $a_3$ is the specific component that directly transfers electrons to molecular oxygen $(O_2)$,which then combines with protons $(H^+)$ to form water $(H_2O)$.

(B) Cytochrome oxidase (Complex-$IV$ of the Electron Transport System) is a multi-subunit enzyme that contains both iron $(Fe)$ and copper $(Cu)$ centers.
Specifically,it contains two heme groups ($a$ and $a_3$) and two copper centers ($Cu_A$ and $Cu_B$).
These metal centers are essential for the final transfer of electrons to oxygen,which is the terminal electron acceptor in the mitochondrial electron transport chain.

(B) Cytochrome oxidase (Complex $IV$) is the final enzyme in the electron transport chain $(ETC)$ that transfers electrons to oxygen,reducing it to water.
Cyanide $(CN^-)$ and azides $(N_3^-)$ act as potent inhibitors of cytochrome oxidase.
They bind to the iron atom in the heme group of the enzyme,preventing the transfer of electrons to oxygen,which effectively halts cellular respiration and $ATP$ production.

(B) Cyanide-resistant respiration is a unique metabolic pathway found in plants,fungi,and some bacteria. It involves an alternative oxidase $(AOX)$ enzyme that bypasses the standard cytochrome $c$ oxidase pathway in the electron transport chain. Among the given options,$Brassica$ (a genus of plants in the mustard family) is known to exhibit cyanide-resistant respiration. Therefore,the correct option is $B$.

(D) The alternative oxidase $(AOX)$ pathway is a branch of the mitochondrial electron transport chain in plants.
It allows electrons to bypass complexes $III$ and $IV$,transferring them directly to oxygen.
This pathway is specifically inhibited by hydroxamic acids.
Both $SHAM$ (Salicylhydroxamic acid) and $m-CLAM$ ($m$-chlorobenzhydroxamic acid) are well-known inhibitors of the alternative oxidase enzyme.
Therefore,both $(B)$ and $(C)$ are correct.

(C) Cyanide $(CN^-)$ acts as a potent inhibitor of the electron transport system $(ETS)$.
It specifically binds to the ferric $(Fe^{3+})$ iron in the heme $a_3$ of cytochrome $c$ oxidase.
Cytochrome $c$ oxidase is known as Complex-$IV$ in the mitochondrial electron transport chain.
By binding to this complex,cyanide prevents the transfer of electrons to oxygen,thereby halting the entire electron transport chain and inhibiting oxidative phosphorylation.

(A) In the Electron Transport System $(ETS)$ of mitochondria,electrons are transferred through a series of complexes.
$Ubiquinone$ ($UQ$ or $Coenzyme-Q$) is a lipid-soluble,small molecule that is not permanently attached to any protein complex.
It acts as a mobile electron carrier that shuttles electrons between $Complex-I$ ($NADH$ dehydrogenase) and $Complex-III$ ($Cytochrome-bc_1$ complex),as well as from $Complex-II$ ($Succinate$ dehydrogenase) to $Complex-III$.
Therefore,$UQ$ is the correct answer.

(A) In both respiration and photosynthesis,the synthesis of $ATP$ occurs through an electron transport system $(ETS)$.
In photosynthesis,this is known as photophosphorylation,which occurs in the thylakoid membranes of chloroplasts.
In respiration,this is known as oxidative phosphorylation,which occurs in the inner mitochondrial membrane.
Both processes utilize a proton gradient across a membrane to drive the enzyme $ATP$ synthase,resulting in the production of $ATP$.

(C) The $F_1$ particles,also known as $F_1$ headpieces or $F_1$ subunits,are part of the $F_0-F_1$ $ATP$ synthase complex located on the inner mitochondrial membrane.
These particles are responsible for the synthesis of $ATP$ from $ADP$ and inorganic phosphate $(Pi)$ using the energy derived from the proton gradient.
This process of synthesizing $ATP$ using energy released during the electron transport chain is known as oxidative phosphorylation.
Therefore,the $F_1$ particles contain the necessary components for oxidative phosphorylation.

(B) $F_1$ particles,also known as $F_1$ subunits or $F_1$ heads,are part of the $F_0-F_1$ $ATP$ synthase complex located in the inner mitochondrial membrane.
These particles contain the catalytic sites for the synthesis of $ATP$ from $ADP$ and inorganic phosphate $(Pi)$.
This process,which is coupled with the electron transport system $(ETS)$,is known as oxidative phosphorylation.
Therefore,$F_1$ particles are essential for oxidative phosphorylation.

(A) In the process of cellular respiration,specifically within the Electron Transport System $(ETS)$,several mineral elements act as essential cofactors for enzymes and electron carriers.
Iron $(Fe)$ is a critical component of cytochromes and iron-sulfur proteins,which are vital for electron transfer.
Copper $(Cu)$ is an essential component of Cytochrome $c$ oxidase (Complex $IV$),which facilitates the final transfer of electrons to oxygen.
Therefore,both Iron and Copper are indispensable for the efficient functioning of the respiratory chain.

(D) Iron is a crucial component of several biological molecules involved in oxygen transport and electron transport.
$1$. Hemoglobin is the protein in red blood cells that carries oxygen throughout the body and contains iron in its heme group.
$2$. Myoglobin is a protein found in muscle tissues that stores oxygen and also contains an iron-based heme group.
$3$. Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain during cellular respiration.
Therefore,all three compounds contain iron.

(B) $FAD$ stands for Flavin adenine dinucleotide.
It is a redox-active coenzyme associated with various proteins, which is involved in several enzymatic reactions in metabolism.
It functions as an electron carrier in the electron transport chain and the citric acid cycle $(Krebs cycle)$.

(D) Oxidative phosphorylation is the synthesis of energy-rich $ATP$ molecules using the energy liberated during the oxidation of reduced coenzymes $(NADH, FADH_2)$ produced during respiration.
The enzyme required for this synthesis is called $ATP$ synthase.
It is located in the $F_1$ headpiece of the $F_0-F_1$ complex (elementary particles) present in the inner mitochondrial membrane.
The $F_1$ particle is capable of $ATP$ synthesis.
$ATP$ synthase becomes active in $ATP$ formation only when there is a proton gradient with a higher concentration of $H^+$ ions on the $F_0$ side compared to the $F_1$ side.
This concentration difference creates an electric potential across the mitochondrial membrane.
The proton gradient and membrane electric potential together form the proton motive force $(PMF)$.
The flow of protons through the $F_0$ channel induces the $F_1$ particle to function as $ATP$ synthase.
The energy of the proton gradient is used to attach a phosphate group to $ADP$ via a high-energy bond,producing $ATP$.

(A) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain $(ETC)$.
In mitochondria,the $ETC$ is located in the inner mitochondrial membrane,which is folded into structures called cristae.
Therefore,cytochromes are found in the cristae of mitochondria.

(C) During the process of cellular respiration,the electron transport system $(ETS)$ is located in the inner mitochondrial membrane. As electrons pass through the various complexes of the $ETS$,energy is released and used to pump protons ($H^+$ ions) from the mitochondrial matrix into the intermembrane space. This creates a proton gradient across the inner membrane,which is essential for the synthesis of $ATP$ by $ATP$ synthase.

(A) : The chemiosmotic coupling hypothesis of oxidative phosphorylation,proposed by $Peter \ Mitchell$,explains the process of $ATP$ formation and states that it is linked to the development of a proton gradient across the inner mitochondrial membrane.
$ATP$ synthase,which is required for $ATP$ synthesis,is located in the $F_1$ particles present on the inner mitochondrial membrane.
This enzyme becomes active only when there is a high concentration of protons on the $F_0$ side (intermembrane space) as compared to the $F_1$ side (matrix).
The flow of protons through the $F_0$ channel induces the $F_1$ particle to function as $ATP$ synthase,and the energy derived from the proton gradient drives the phosphorylation of $ADP$ to form $ATP$.

(C) The chemiosmotic hypothesis explains $ATP$ synthesis in mitochondria and chloroplasts.
According to this hypothesis,$ATP$ synthesis is linked to the development of a proton gradient across the membrane.
Complex $V$ ($ATP$ synthase) is the enzyme responsible for $ATP$ synthesis.
It consists of two major components: $F_1$ and $F_0$.
$F_1$ is a peripheral membrane protein complex that contains the site for $ATP$ synthesis,while $F_0$ is an integral membrane protein complex that forms a channel through which protons cross the membrane.

(D) In the mitochondrial electron transport chain $(ETC)$,Cytochrome $C$ is a small protein attached to the outer surface of the inner mitochondrial membrane.
It acts as a mobile electron carrier that transfers electrons between Complex $III$ (Cytochrome $bc_1$ complex) and Complex $IV$ (Cytochrome $c$ oxidase complex).
Other cytochromes like $a$ and $a_3$ are integral parts of the complexes and are not mobile carriers.

(B) In the Electron Transport System $(ETS)$,the complexes are organized as follows:
- Complex $I$: $NADH$ dehydrogenase.
- Complex $II$: $Succinate$ dehydrogenase.
- Complex $III$: $Cytochrome \, bc_1$ complex.
- Complex $IV$: $Cytochrome \, c$ oxidase.
- Complex $V$: $ATP$ synthase.
Therefore,Complex $III$ is the $Cytochrome \, bc_1$ complex.

(B) In the Electron Transport System $(ETS)$ located in the inner mitochondrial membrane,various complexes are involved in the transfer of electrons.
Complex $I$ is $NADH$ dehydrogenase.
Complex $II$ is Succinate dehydrogenase.
Complex $III$ is the Cytochrome $bc_1$ complex.
Complex $IV$ is Cytochrome $c$ oxidase.
Therefore,the Cytochrome $bc_1$ complex corresponds to Complex $III$.

(B) Assertion $(A)$ is incorrect because protons are transported from the intermembrane space to the matrix through the $F_0$ channel,which then drives the $F_1$ headpiece to synthesize $ATP$. The direction is from $F_0$ to $F_1$ (or rather,$F_0$ acts as the channel for protons to move into the matrix).
Reason $(R)$ is incorrect because the oxidation of $NADH$ (or $NADPH_2$) occurs at Complex-$I$ ($NADH$ dehydrogenase) in the inner mitochondrial membrane,not in the $F_1$ particle of the $ATP$ synthase enzyme. $F_1$ is specifically involved in the phosphorylation of $ADP$ to $ATP$.

(B) In the Electron Transport System $(ETS)$,Complex $II$ is known as Succinate dehydrogenase.
This complex oxidizes succinate to fumarate and transfers electrons to ubiquinone via $FADH_2$.
Since the original options provided were incorrect or incomplete,the correct biological identity of Complex $II$ is Succinate dehydrogenase.

(C) The $Kreb's$ cycle (also known as the citric acid cycle) occurs in the mitochondrial matrix.
Similarly,the Electron Transport System $(ETS)$ is located on the inner mitochondrial membrane.
This membrane contains the protein complexes ($I$ to $IV$) and $ATP$ synthase required for oxidative phosphorylation.
Therefore,the correct location for $ETS$ reactions is the inner mitochondrial membrane.

(C) Oxidative phosphorylation is the process in which $ATP$ is synthesized using the energy released during the oxidation of reduced coenzymes ($NADH$ and $FADH_2$) through the Electron Transport System $(ETS)$.
Because this process occurs via the $ETS$ located in the inner mitochondrial membrane,it is commonly referred to as the Electron Transport System $(ETS)$ or Electron Transport Chain $(ETC)$.

(B) The $F_0-F_1$ particle,also known as $ATP$ synthase,is responsible for the synthesis of $ATP$ during oxidative phosphorylation.
According to the chemiosmotic hypothesis,the movement of protons $(H^+)$ from the intermembrane space into the mitochondrial matrix through the $F_0$ channel drives the conformational changes in the $F_1$ subunit.
It is established that the passage of $2$ protons $(H^+)$ through the $F_0-F_1$ complex results in the synthesis of $1$ molecule of $ATP$ from $ADP$ and inorganic phosphate $(Pi)$.

(A) The $ATPase$ enzyme complex consists of two major components: $F_0$ and $F_1$.
The $F_0$ part is an integral membrane protein complex that forms a channel through which protons cross the inner mitochondrial membrane.
The $F_1$ headpiece is a peripheral membrane protein complex located on the matrix side of the inner mitochondrial membrane.
$F_1$ contains the catalytic site for the synthesis of $ATP$ from $ADP$ and inorganic phosphate $(Pi)$.
Since both statements $A$ and $R$ accurately describe the structure and function of the $ATPase$ complex,both are correct.

(B) During aerobic respiration,$1$ molecule of pyruvic acid undergoes the following steps:
$1$. Link reaction: $1$ $NADH$ is produced.
$2$. Krebs cycle: $4$ $NADH$,$1$ $FADH_2$,and $1$ $GTP$ $(ATP)$ are produced.
Total per pyruvic acid: $5$ $NADH$ and $1$ $FADH_2$.
For $3$ pyruvic acid molecules: $15$ $NADH$ and $3$ $FADH_2$.
Oxidative phosphorylation involves the electron transport system $(ETS)$ where $1$ $NADH$ yields $3$ $ATP$ and $1$ $FADH_2$ yields $2$ $ATP$.
Total $ATP$ from $NADH = 15 \times 3 = 45$.
Total $ATP$ from $FADH_2 = 3 \times 2 = 6$.
Total $ATP$ via oxidative phosphorylation = $45 + 6 = 51$.
However,if we consider the standard $P$/$O$ ratio where $1$ $NADH = 2.5$ $ATP$ and $1$ $FADH_2 = 1.5$ $ATP$:
Total $ATP = (15 \times 2.5) + (3 \times 1.5) = 37.5 + 4.5 = 42$.
Given the options,$42$ is the correct value based on the modern $P$/$O$ ratio.

(A) In the Electron Transport System $(ETS)$ located in the inner mitochondrial membrane,various complexes are involved in the transfer of electrons.
Complex $I$ is $NADH$ dehydrogenase,which accepts electrons from $NADH + H^+$.
Complex $II$ is succinate dehydrogenase (which uses $FADH_2$).
Complex $III$ is cytochrome $bc_1$ complex.
Complex $IV$ is cytochrome $c$ oxidase,which contains cytochromes $a$ and $a_3$ and two copper centers.
Therefore,complex $I$ is $NADH$ dehydrogenase and complex $IV$ is cytochrome $c$ oxidase.