Problem 82 - Objective Biology for NEET

Question

Oxidative phosphorylation occurs in the (a) Outer membrane of mitochondria (b) Inner membrane of mitochondria (c) Stroma of chloroplast (d) Grana of chloroplast

Step-by-Step Solution

Answer

The oxidative phosphorylation occurs in the inner membrane of mitochondria (option b).

Step 1: Understand oxidative phosphorylation

Oxidative phosphorylation is a metabolic process that uses energy released by the oxidation of nutrients to produce Adenosine Triphosphate (ATP).

Step 2: Identify the location of oxidative phosphorylation

Oxidative phosphorylation takes place in the mitochondria. However, it doesn't occur in the outer membrane, but in the inner membrane where proteins of the electron transport chain are located.

Key Concepts

Mitochondria

Mitochondria are often referred to as the "powerhouses" of the cell. These small, bean-shaped organelles are critical for generating energy in the form of ATP. ATP, or Adenosine Triphosphate, acts like a rechargeable battery that powers cellular processes. Each mitochondrion is equipped with two membranes: an outer membrane and an inner membrane.

The outer membrane serves as a boundary and a gateway that allows small molecules to enter and exit the mitochondria. It is relatively permeable due to porins, which are channels that allow small molecules to diffuse freely. On the other hand, the inner membrane is much less permeable, playing a key role in energy transformation.

Inside the mitochondria, we find the matrix, a fluid-filled space containing enzymes essential for metabolic reactions. The inner membrane folds extensively into structures called cristae, increasing the surface area for chemical reactions to occur. This unique design optimizes the mitochondria's ability to produce ATP, making them highly efficient energy converters.

Inner Membrane

The inner membrane of mitochondria is where the magic of oxidative phosphorylation takes place. Unlike the outer membrane, it is selectively permeable and packed with proteins. These proteins are crucial for various functions, including the electron transport chain and ATP production. The inner membrane's selective permeability ensures that only necessary ions and molecules can move across, maintaining optimal conditions for ATP production.

The inner membrane is studded with a number of important protein complexes forming the electron transport chain. Additionally, it also houses ATP synthase, an enzyme that synthesizes ATP from ADP (Adenosine Diphosphate) and inorganic phosphate. This enzyme uses a gradient of protons, also known as a proton-motive force, generated by the electron transport chain.

The extensive folding of the inner membrane into cristae increases surface area and supports the large number of electron transport chains and ATP synthase complexes needed to meet the cell's energy demands. In summary, the inner membrane is highly specialized and adapted to making cellular respiration as efficient as possible.

Electron Transport Chain

At the heart of oxidative phosphorylation is the electron transport chain (ETC), a series of protein complexes located in the mitochondria's inner membrane. During ETC, electrons derived from molecules like NADH and FADH extsubscript{2} are passed along these complexes. As these electrons move down the chain, they release energy.

This energy is used to pump protons (H extsuperscript{+} ions) from the mitochondrial matrix to the intermembrane space, creating an electrochemical gradient known as the proton-motive force. The accumulation of protons in the intermembrane space creates a high concentration that naturally wants to equalize by moving back into the matrix.

ATP synthase, another key player situated in the inner membrane, capitalizes on this proton gradient. As protons flow back into the matrix through ATP synthase, the enzyme uses this flow to synthesize ATP from ADP and inorganic phosphate. This process not only drives ATP creation but also links electron transport and energy storage, making ETC a fundamental part of cellular respiration.