Which factors determine the specificity of protein binding?

• A. Protein shape alone
• B. Protein chemistry alone
• C. Both protein shape and protein chemistry
• D. Temperature

Answer: (C)

Specific binding depends on two features: the shape of the binding site and the chemical properties of the amino acids forming that site. Shape complementarity ensures the target fits snugly, like puzzle pieces fitting together. The chemistry provides the specific interactions—hydrogen bonds, ionic interactions, and hydrophobic contacts—that recognize particular groups on the target. When both shape and chemistry align, the interaction is strong and highly selective for that partner. Temperature can influence binding by altering motion and stability, potentially weakening interactions or promoting non-specific contacts, but it does not set the fundamental specificity. So, the specificity arises from the combination of protein shape and protein chemistry.