MCQ on Electron Transport System

Located within the inner mitochondrial membrane, the ETS (Electron Transport System) or electron transport chain performs its functions. Several electron transporters are linked together in a series, which makes it easier for electrons to travel from one carrier to another during redox processes. The oxidation of the NADH and FADH2 generated during the citric acid cycle occurs. The establishment of a proton gradient across the membrane results, which drives the production of ATP via oxidative phosphorylation during the process of cellular respiration, as previously stated.

1. Which of the following is the correct sequence of electron acceptors in ETS for production of ATP?

(a) Cyt b, c, a, a3

(b) Cyt a, a, b, c

(c) Cyt c, b, a, a3

(d) Cyt b, c, a3, a

Answer: (a)

As a result, the correct order of electron acceptors in ATP production is Cyt. b, c, a, and a3.

2. Which of the following terminal cytochromes is responsible for the transfer of electrons from oxygen to other molecules?

(a) Cyt a3

(b) Cyt b

(c) Cyt c

(d) Cyt a1

Answer: (a)

Cytochromes a3 are a kind of chromophore. A subgroup of heme A cytochromes with an alpha-band absorption wavelength of 605 nm that belong to the heme A superfamily. Their presence in a number of bacteria and eukaryotes is due to their presence in the MITOCHONDRIAL ELECTRON TRANSPORT COMPLEX IV, which is composed of high-spin cytochrome components.

3. Which of the following sections of the mitochondria contains the electron transport system (ETS)?

(a) Inner membrane

(b) Outer membrane

(c) Matrix

(d) Stroma

Answer: (a)

inner mitochondrial membrane

Located within the inner mitochondrial membrane, the ETS (Electron Transport System) or electron transport chain performs its functions. Several electron transporters are linked together in a series, which makes it easier for electrons to travel from one carrier to another during redox processes.

4. Which of the following is the initial complex (Complex I) of the ETS?

(a) NADH dehydrogenase

(b) Cytochrome aa3

(c) Cytochrome bc1

(d) ATP synthase

Answer: (a)

In the mitochondria, NADH dehydrogenase is the first enzyme complex of the electron transport chain, and it is responsible for the production of NADH. It is responsible for converting NADH, the reduced form of nicotinamide adenine dinucleotide (NAD), to NAD+, the oxidised form of the compound.

5. Which of the following ETS Complexes is Complex III?

(a) NADH dehydrogenase

(b) Cytochrome aa3

(c) Cytochrome bc1

(d) ATP synthase

Answer: (c)

Cytochrome bc1 (Cbc1) is a cytochrome that serves as a key pump for the movement of protons across the cell membrane. The protons are used to generate the rotational energy required by ATP synthase. Cbc1 binds to ubiquinol, which is a molecule that transports hydrogen atoms. Cbc1 is responsible for the separation of protons and electrons.

6. Ubiquinone transfers electrons from one atom to another.

(a) Complex I

(b) Complex II

(c) matrix

(d) Cyt c

Answer: (d)

In the mitochondrial membrane compartment between the inner and outer mitochondrial membranes, cytochrome c is a heme protein that serves to transmit electrons between complex III and IV of the respiratory chain. Cytochrome c is a red blood cell component.

7. Where exactly does oxidative phosphorylation take place in the cell?

(a) Membrane of the inner mitochondrial membrane

(b) Membrane of the outer mitochondrial membrane

(c) Grana of chloroplast

(d) Stroma of chloroplast

Answer: (a)

It is oxidative phosphorylation, which takes place within mitochondria, that generates the vast majority of the usable energy derived from the breakdown of carbohydrates or fatty acids.

8. Cytochromes are found in a variety of organisms.

(a) lysosomes

(b) mitochondrial matrix

(c) cristae of mitochondria

(d) outer membrane of mitochondria

Answer: (c)

A crista is a fold in the inner membrane of a mitochondrion that serves as a structural component. The word derives from the Latin for crest or plume, and it is responsible for the unique wrinkled structure of the inner membrane, which provides a high amount of surface area for chemical reactions to take place on.

9. The mobility of the mitochondria drives the creation of ATP by the ATP synthase.

(a) protons

(b) NADH

(c) electrons

(d) All of the above

Answer: (a)

An enzyme found in the inner membrane of mitochondria, ATP synthase is responsible for catalysing the synthesis of ATP from ADP and phosphate. This is accomplished through the movement of protons across an electrochemical gradient generated by electron transfer from the proton’s chemically positive to negative side.

10. The creation of oxidative phosphorylation occurs in the production of

(a) Oxygen

(b) ADP

(c) ATP + H₂O

(d) NADH

Answer: (c)

It is through the reaction of ADP and phosphate that ATP is formed from water. 

ADP + Pi + free energy →ATP+H₂O.

11. Which of the following complexes of ETS is not responsible for the pumping out of protons from the mitochondrial matrix? 

(a) Complex I

(b) Complex III

(c) Complex II

(d) Complex IV

Answer: (c)

Succinate dehydrogenase (Complex II) catalyses the oxidation of succinate to fumarate in the mitochondrial Krebs cycle as well as the transfer of electrons from succinate to ubiquinone in the mitochondrial electron transport chain, which is essential for respiration (ETC).

12. Which of the following is the ETS Complex IV?

(a) NADH dehydrogenase

(b) Cytochrome c oxidase

(c) Cytochrome bc1

(d) Succinate dehydrogenase

Answer: (b)

Cytochrome c oxidase (CcO) is an enzyme that converts respiratory energy into chemical energy. As it catalyses the transfer of electrons from cytochrome c to molecular oxygen, it conserves the energy released by the transfer by creating a charge and proton gradient across the membrane in which it is situated.

13. Which of the following is the Complex II of ETS?

(a) NADH dehydrogenase

(b) Succinate dehydrogenase

(c) Cytochrome bc1

(d) ATP synthase

Answer: (b)

This combination of enzymes, known as succinate dehydrogenase (SDH) or succinate-coenzyme Q reductase (SQR) or respiratory complex II, can be found in the inner mitochondrial membrane of eukaryotes and in the outer mitochondrial membrane of bacteria. Because it participates in both the citric acid cycle and the electron transport chain, it is the only enzyme in the body that can do so.