Question

T cell receptors or antibodies react with antigens

• A. \( \text{because both are made by lymphocytes} \)
• B. \( \text{because of complementary of molecular fit of both with antigen} \)
• C. \( \text{because both 'have light chain and heavy chain polypeptides} \)
• D. \( \text{cause histamine release} \)

Hint:

The specific region on the antibody that binds to the antigen is called the Paratope.

Answer 1

The Correct Option is B

Concept: The interaction between the immune system and a pathogen is highly specific.
• Antibodies and T-cell receptors (TCRs) must "recognize" a specific part of the antigen.
• This part of the antigen is called the epitope.

Step 1: The Principle of Specificity.
The binding between an antibody/TCR and an antigen is often compared to a "Lock and Key" mechanism. The physical shape of the receptor's binding site must match the physical shape of the antigen's epitope.

Step 2: Molecular Fit and Forces.
The reaction occurs because the surfaces of the molecules have a "complementary" molecular fit. This fit allows weak non-covalent forces (like hydrogen bonds and van der Waals forces) to hold the molecules together. Without this precise structural complementarity, the immune receptor would not bind to the antigen. Final Answer: Receptors react with antigens because of the complementary molecular fit between the two.