Question

Match the column: Column I Column II A. NADH dehydrogenase \- 1. Complex IV B. Cytochrome \(\mathrm{bc}_{1}\) 2\. Complex III C. Cytochrome \(\mathrm{aa}_{3}\) 3\. Complex I D. ATP synthase 4\. Complex V (a) A-1, B-2, C-3, D - - (b) \(\mathrm{A}-3, \mathrm{~B}-2, \mathrm{C}-1, \mathrm{D}-4\) (c) \(\mathrm{A}-4, \mathrm{~B}-1, \mathrm{C}-3, \mathrm{D}-2\) (d) \(\quad \mathrm{A}-1, \mathrm{~B}-4, \mathrm{C}-2, \mathrm{D}-3\)

Short answer

The correct answer is (b) A-3, B-2, C-1, D-4.

Step-by-step solution

Recognizing the Enzymes

Start by identifying each enzyme with its full name. NADH dehydrogenase is also known as Complex I, cytochrome bc1 is Complex III, cytochrome aa3 is Complex IV, and ATP synthase is Complex V of the electron transport chain.

Matching the Enzymes with Their Complex Numbers

Next, match each of these to their correct notation from the options given. A corresponds to 3 (NADH dehydrogenase is Complex I), B corresponds to 2 (cytochrome bc1 is Complex III), C corresponds to 1 (cytochrome aa3 is Complex IV), and D corresponds to 4 (ATP synthase is Complex V).

Identifying the Correct Option

Following the matching from step 2, check the options provided. The option that matches A-3, B-2, C-1, D-4 is the correct answer.

Key concepts

NADH dehydrogenase

In the context of cellular respiration, NADH dehydrogenase plays a pivotal role. It is the first enzyme and entry point in the electron transport chain (ETC), hence its alternative name, Complex I. Complex I's main function is to oxidize NADH, a high-energy molecule produced during earlier stages of respiration, transferring the electrons to ubiquinone (CoQ), a mobile electron carrier within the mitochondrial inner membrane.

NADH dehydrogenase is a large enzymatic complex containing flavin mononucleotide (FMN) and several iron-sulfur (Fe-S) clusters. These components allow the enzyme to perform redox reactions—that is, the transfer of electrons. During this process, it also aids in pumping protons (H+) across the inner mitochondrial membrane, generating a proton gradient essential for ATP synthesis.

Cytochrome complex

The cytochrome complex, specifically the cytochrome bc1 complex referred to in the exercise as Complex III in the ETC, is crucial for life as it mediates the transfer of electrons from ubiquinol to cytochrome c. The process also contributes to the proton gradient by translocating protons across the mitochondrial membrane.

This complex includes multiple cytochromes, proteins with heme groups that can undergo oxidation and reduction. As Complex III cycles between reduced and oxidized states through the Q cycle, it strategically moves protons into the intermembrane space, further energizing the gradient for ATP production. Cytochrome c, the electron acceptor for Complex III, is a small soluble protein that shuttles electrons to the final complex.

ATP synthase

ATP synthase, also known as Complex V, is the molecular machine responsible for synthesizing ATP, the cellular energy currency, using the proton gradient created by the other complexes of the ETC. It is a highly complex enzyme with two main components: F0, the proton channel embedded in the mitochondrial membrane, and F1, the catalytic unit that synthesizes ATP.

The proton-motive force generated across the membrane drives protons through F0, causing the rotation of a part of the enzyme. This rotation then leads to conformational changes in the F1 unit, catalyzing the conversion of ADP and inorganic phosphate into ATP. ATP synthase operates with incredible efficiency and is a beautiful demonstration of energy conversion in biology.

NEET Biology

NEET (National Eligibility cum Entrance Test) is a significant pre-medical exam in India that covers various topics, including Biology - a critical subject within it. NEET Biology syllabus includes a diverse range of concepts from botany and zoology, with a heavy focus on human physiology, genetics, evolution, and ecology. The Electron Transport Chain, and specifically understanding the role of NADH dehydrogenase, the cytochrome complex, and ATP synthase, is an integral part of Cell Biology and Bioenergetics within the NEET Biology curriculum.

NEET aspirants must master these concepts, as questions often test a deep understanding of biological processes and their applications to human health and disease. Students who aim to score well on the NEET exam need to grasp the interplay between different biochemical pathways and their significance in the larger context of physiological functions.