Answer:
b. Active site
Explanation:
The active site of an enzyme, also called the active center, is the area of the enzyme to which the substrate binds, so that the reaction occurs.
Enzymes are proteins. Certain characteristics in its tertiary structure are those that determine the shape of the active site of the enzyme, and therefore delimit the substrates on which the enzyme can act. In other words, the three-dimensional structure of the enzyme also determines the structure of the active site, and gives specificity to the enzyme, which can only act on certain substrates: those capable of binding to its active site.
Many times, the active site has the shape of a cleft or a cavity in the structure of the enzyme. The active site is usually formed by side chains of specific residues, and it is for this reason that it often has a three-dimensional structure different from the rest of the enzyme. The structure and composition of the active center is configured so that only a certain substrate has sufficient affinity to bind to this area of the enzyme
