Receptors show selectivity for one chemical messenger over other because of different
I.Shape of binding site
II.structure of binding site
III.amino acid composition of binding site Which of the following is the correct option?

Options

A. I and II
B. II and III
C. I and III
D. all of these

Answer

To solve the question regarding the selectivity of receptors for chemical messengers, we can break it down into a step-by-step analysis of the statements provided.

### Step-by-Step Solution

1. **Understanding Receptors**: Receptors are specialized proteins located on cell surfaces or within cells that bind to specific chemical messengers (like hormones or neurotransmitters). This binding triggers a response in the cell.

2. **Analyzing the Statements**:
- **Statement I: Shape of Binding Site**: The shape of the binding site is crucial because it determines which chemical messenger can fit into the receptor. Just like a key fits into a specific lock, only certain messengers will fit into the receptor's binding site due to its shape.

- **Statement II: Structure of Binding Site**: The overall structure of the binding site, which includes its three-dimensional arrangement, is also important. Different receptors have different structural configurations, which contribute to their specificity for certain chemical messengers.

- **Statement III: Amino Acid Composition of Binding Site**: The specific amino acids that make up the binding site influence how the receptor interacts with various chemical messengers. Different amino acids can create different chemical environments, which can enhance or inhibit the binding of certain messengers.

3. **Conclusion**: Since all three statements (I, II, and III) contribute to the selectivity of receptors for chemical messengers, we conclude that they are all correct. Therefore, the correct option is that all of these factors contribute to receptor selectivity.

### Final Answer
The correct option is **all of these** (option number 4).

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