An individual molecular structure within an antigen to which an individual antibody binds is an :

Options

A. hinge region
B. epitope
C. Fab region
D. FC region

Answer

To solve the question, "An individual molecular structure within an antigen to which an individual antibody binds is an:", we will analyze the options provided and understand the relevant concepts related to antibodies and antigens.

### Step-by-Step Solution:

1. **Understanding Antigens and Antibodies**:
- Antigens are substances that can induce an immune response, typically proteins or polysaccharides found on the surface of pathogens.
- Antibodies are proteins produced by the immune system that specifically bind to antigens.

2. **Identifying Key Terms**:
- **Hinge Region**: This is a part of the antibody structure that provides flexibility, allowing the antibody to bind to antigens effectively. It is not a part of the antigen.
- **FAB Region**: This is the fragment of the antibody that binds to the antigen. It is composed of variable regions that are specific to each antigen.
- **FC Region**: This is the constant region of the antibody that interacts with other components of the immune system. It does not bind to the antigen.
- **Epitope**: This is the specific part of the antigen that is recognized and bound by an antibody. It is the molecular structure on the antigen that the antibody targets.

3. **Analyzing the Options**:
- The question asks for the structure within the antigen that an antibody binds to.
- Since the hinge, FAB, and FC regions are all parts of the antibody, they cannot be correct answers.
- The only option that refers to a part of the antigen is "epitope".

4. **Conclusion**:
- The correct answer is **epitope**. This is the specific molecular structure on the antigen that binds to the antibody.

### Final Answer:
The correct answer is **epitope**.

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