Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Electron transport chain (ETC) and ATP synthesizing system are located on the inner mitochondrial membrane.
Reason R: The inner surface of the inner mitochondrial membrane possess phosphorylating subunits.

• A. Both A and R are correct and R is the correct explation of A
• B. Both A and R are correct but R is NOT the correct explation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Hint:

Inner Mitochondrial Membrane = Site of ETC complexes + ATP Synthase ($F_0F_1$ particles).
$F_1$ particle projects into the matrix and contains catalytic sites for ADP + $\text{P}_i \to$ ATP.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question deals with the submitochondrial localization of electron transport chain complexes and ATP synthase subunits involved in oxidative phosphorylation.

Step 2: Key Formula or Approach:
Oxidative phosphorylation requires structural organization within the inner mitochondrial membrane (IMM). Respiratory complexes I–IV pump protons into the intermembrane space, creating a proton gradient that drives ATP synthesis via $F_0F_1$-ATP synthase.

Step 3: Detailed Explation:

• Alysis of Assertion A: The enzymes of the Electron Transport Chain (Complexes I, II, III, and IV) and the ATP synthesizing complex (Complex V ATP synthase) are physically embedded within the inner mitochondrial membrane. Thus, Assertion A is correct.

• Alysis of Reason R: The inner surface (matrix-facing side) of the inner mitochondrial membrane contains the spherical $F_1$ catalytic heads ($F_1$ phosphorylating subunits) of ATP synthase, connected via a stalk to the membrane-embedded $F_0$ proton channel. These $F_1$ subunits carry out the phosphorylation of ADP to ATP. Thus, Reason R is correct.

• Causal Relationship: The structural presence and orientation of these catalytic phosphorylating subunits ($F_1$) coupled to the electron transport complexes on the inner mitochondrial membrane explains how mitochondrial energy transduction is executed at this membrane site. Thus, R is the correct explation of A.

Step 4: Fil Answer:
Both A and R are correct and R is the correct explation of A.