The initial step in the biosynthesis of ATP by chemiosmosis in the mitochondrion is the -

Options

A. Pumping of protons in the outer chamber
B. Pumping of electrons in the matrix
C. Action of ATP synthase
D. Formation of metabolic water

Answer

### Step-by-Step Solution:

1. **Understanding the Process**: The biosynthesis of ATP in mitochondria occurs through a process called chemiosmosis, which involves the movement of protons (H⁺ ions) across a membrane.

2. **Proton Pumping**: The initial step in this process is the establishment of a proton gradient. Protons are pumped from the mitochondrial matrix into the intermembrane space, creating a higher concentration of H⁺ ions outside the matrix.

3. **Formation of a Concentration Gradient**: This pumping creates a concentration gradient of protons, where there is a higher concentration of H⁺ ions in the intermembrane space compared to the matrix. This difference in concentration is crucial for ATP synthesis.

4. **Role of ATP Synthase**: The ATP synthase complex, which consists of two main components (F₀ and F₁), utilizes this proton gradient. As protons flow back into the matrix through ATP synthase, the energy released is used to convert ADP and inorganic phosphate (Pi) into ATP.

5. **Final Steps**: The movement of protons through ATP synthase leads to the synthesis of ATP. Additionally, the electrons that were part of the electron transport chain eventually combine with protons and oxygen to form water, but this is a later step in the process.

### Final Answer:
The initial step in the biosynthesis of ATP by chemiosmosis in the mitochondrion is the **pumping of protons (H⁺ ions) from the mitochondrial matrix into the intermembrane space, creating a proton gradient**.

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