Final answer:
The variable regions of TCRs and BCRs enable binding to antigens, allowing the immune system to recognize a multitude of different antigens through genetic rearrangement.
Step-by-step explanation:
Regions of TCRs (T cell receptors) and BCRs (B cell receptors) that are variable in their amino acid sequences are particularly known for binding to antigens. Variable regions are the parts of these receptor molecules that determine specificity for different antigens, allowing T cells and B cells to recognize a vast array of possible antigens through genetic rearrangement, which contributes to the immune system's diversity. TCRs consist of two chains, each with a variable and a constant region, and they span the plasma membrane to project variable binding regions into the extracellular space to bind processed antigens via MHC molecules on APCs. BCRs are also membrane-bound and use their Fab antigen-binding regions to bind specific antigen epitopes with diversity achieved through similar genetic rearrangements.