Question

Application of which of the following inhibitors will prevent electrons from reaching oxygen? I. Oligomycin II. Rotenone and antimycin A III. Cyanide and carbon monoxide A. I only B. II and III only C. II only D. I, II, and III

Short answer

B. II and III only

Step-by-step solution

Understand the Context

Electrons being transferred to oxygen is a critical process in cellular respiration, specifically in the electron transport chain (ETC) in the mitochondria.

Identify Roles of Inhibitors

Determine which inhibitors affect the electron transport chain:- Oligomycin: Inhibits ATP synthase, not directly blocking electron transfer.- Rotenone: Inhibits complex I, preventing electron transfer from NADH to ubiquinone.- Antimycin A: Inhibits complex III, preventing electron transfer from ubiquinone to cytochrome c.- Cyanide and Carbon Monoxide: Inhibit complex IV, preventing electron transfer to oxygen.

Evaluate Each Option

Analyze each option based on the roles:- **Option A**: I only (incorrect, Oligomycin does not prevent electron transfer)- **Option B**: II and III only (correct, both inhibits critical steps in electron transport)- **Option C**: II only (incorrect, does not include cyanide and carbon monoxide)- **Option D**: I, II, and III (incorrect, includes Oligomycin which is not relevant)

Select the Correct Answer

Based on the analysis, the correct answer is B. Both Rotenone and Antimycin A (II) and Cyanide and Carbon Monoxide (III) prevent electrons from reaching oxygen.

Key concepts

cellular respiration

Cellular respiration is a vital process that cells use to convert nutrients into energy.
This energy is stored in a molecule called adenosine triphosphate (ATP).
In eukaryotic cells, cellular respiration happens in the mitochondria and involves several stages.
Glycolysis occurs in the cytoplasm, where glucose is split into two molecules of pyruvate, generating a small amount of ATP and NADH.
The Citric Acid Cycle (also known as the Krebs Cycle) processes these pyruvate molecules to produce ATP, NADH, and FADH2.
The most significant amount of ATP, however, is produced in the final stage: the electron transport chain (ETC). This stage is crucial for generating the majority of the cell's energy.

electron transport chain

The Electron Transport Chain (ETC) is a series of protein complexes located in the inner mitochondrial membrane.
Its main role is to transfer electrons from electron donors to electron acceptors through redox reactions.
These redox reactions release energy, which is then used to pump protons across the mitochondrial membrane, creating a proton gradient.
This proton gradient drives the synthesis of ATP through a process called chemiosmosis.
The electron transport chain involves several key complexes:

• Complex I: NADH dehydrogenase receives electrons from NADH.
• Complex II: Succinate dehydrogenase receives electrons from FADH2.
• Complex III: Cytochrome bc1 complex receives electrons from ubiquinone and transfers them to cytochrome c.
• Complex IV: Cytochrome c oxidase transfers electrons to oxygen, forming water.
  

Inhibitors of the ETC, such as Rotenone, Antimycin A, Cyanide, and Carbon Monoxide, can block electron flow, preventing ATP synthesis.

mitochondrial complexes

Mitochondrial complexes play a crucial role in cellular respiration by facilitating the electron transport chain.
There are four main complexes and each has a unique function:

• **Complex I (NADH dehydrogenase)**: Accepts electrons from NADH and transfers them to ubiquinone. The inhibitors like Rotenone block this complex.
• **Complex II (Succinate dehydrogenase)**: Transfers electrons from succinate to ubiquinone, contributing to the pool of electrons flowing into Complex III.
• **Complex III (Cytochrome bc1 complex)**: Transfers electrons from ubiquinone to cytochrome c. Inhibitors like Antimycin A hinder this complex.
• **Complex IV (Cytochrome c oxidase)**: Transfers electrons from cytochrome c to oxygen, producing water. Cyanide and Carbon Monoxide inhibit this step, blocking electron transfer to oxygen.
  

These complexes collectively help maintain the proton gradient across the inner mitochondrial membrane, which is essential for ATP production.