Problem 22 - Objective Biology for NEET

Question

1 molecule of NADH gives rise to molecules of ATP, while 1 molecule of FADH \(_{2}\) gives molecule of ATP (a) 3,2 (b) 2,3 (c) 2,2 (d) 3,3

Step-by-Step Solution

Answer

The correct answer is (a) 3,2.

Step 1: Understand the Role of NADH and FADH2 in Cellular Respiration

In the process of cellular respiration, NADH and FADH2 molecules serve as electron carriers. These carriers move electrons to the electron transport chain, where ATP is produced.

Step 2: Know the amount of ATP produced per carrier

From biological science, it is known that one NADH molecule typically contributes to making approximately 3 ATP molecules, whereas one FADH2 produces about 2 ATP molecules.

Step 3: Match the facts with answer choices

According to the information from the previous step, 1 molecule of NADH gives rise to 3 ATP molecules, and 1 FADH2 molecule gives rise to 2 ATP molecules. The only choice that matches this is (a) 3,2.

Key Concepts

NADH

NADH stands for nicotinamide adenine dinucleotide (NAD) in its reduced form with an added hydrogen ion (H). It is a critical molecule in cellular respiration. During the breakdown of glucose in glycolysis and the citric acid cycle, NADH serves as an electron carrier.

• NADH is formed when NAD extsuperscript{+}, a coenzyme, accepts electrons from biochemical reactions.
• It acts as a shuttle, capturing electrons and donating them to the electron transport chain (ETC) in mitochondria.
• In the ETC, NADH donates electrons at the beginning of the chain, which generates more proton pumping than electrons from FADH extsubscript{2}.

Ultimately, one molecule of NADH contributes enough energy to produce approximately 3 molecules of ATP. This efficiency is crucial for sustaining high-energy processes in living organisms.

FADH2

FADH extsubscript{2}, or flavin adenine dinucleotide in its reduced form, is another essential electron carrier in cellular respiration. It operates similarly to NADH but with some key differences.

• FADH extsubscript{2} is generated from FAD during the citric acid cycle, specifically through the oxidation of succinate to fumarate.
• While NADH transfers its electrons to the first protein of the electron transport chain, FADH extsubscript{2} feeds electrons into the chain at a slightly later point.
• This means fewer protons are pumped across the mitochondrial membrane, ultimately leading to less ATP production compared to NADH.

One molecule of FADH extsubscript{2} typically contributes to the formation of about 2 molecules of ATP, reflecting its role in energy conversion during cellular respiration.

Cellular Respiration

Cellular respiration is the metabolic process cells use to extract energy from organic molecules. It can be understood in three main stages: glycolysis, the citric acid cycle, and oxidative phosphorylation.

• Glycolysis: The initial breakdown of glucose into pyruvate, yielding 2 ATP molecules and 2 NADH molecules.
• Citric Acid Cycle: Pyruvate is further broken down in the mitochondria, producing additional NADH and FADH extsubscript{2} molecules.
• Oxidative Phosphorylation: This involves the electron transport chain where NADH and FADH extsubscript{2} donate electrons, leading to ATP synthesis.

Overall, cellular respiration converts the energy stored in glucose into ATP, the energy currency of the cell, which is essential for cellular functions.

Electron Transport Chain

The Electron Transport Chain (ETC) is the final stage of cellular respiration. It is located in the inner mitochondrial membrane and is crucial for ATP production.

• Electrons are transferred from NADH and FADH extsubscript{2} to protein complexes and electron carriers within the chain.
• This transfer process creates a proton gradient across the inner mitochondrial membrane.
• The flow of protons back into the mitochondrial matrix through ATP synthase drives the production of ATP from ADP and inorganic phosphate.

While NADH enters the ETC at the beginning, producing around 3 ATP per molecule, FADH extsubscript{2} enters at a later stage, yielding around 2 ATP per molecule. This complex and efficient process shows how cells convert biochemical energy into a form usable for biological processes.