Final answer:
The active site of an enzyme is where the substrate binds, representing only a small part of the enzyme's total structure. It includes a binding and a catalytic site specific to the substrate, and enzymes are not consumed during the reaction they catalyze.
Step-by-step explanation:
The active site of an enzyme is a crucial region where the substrate binds to initiate a biochemical reaction. This site typically includes two distinct areas: the substrate-binding site and the catalytic site, where the enzymatic catalysis occurs. The active site represents only a small portion of the enzyme, often around 10% to 20%. Amino acid residues such as tyrosine, histidine, cystine, glutamic acid, aspartic acid, lysine, and serine are commonly found in the catalytic site of an enzyme. These specific residues facilitate the chemical reaction through interactions like hydrogen bonding and acting as acids, bases, electrophiles, or nucleophiles.
Enzymes demonstrate a high degree of specificity, meaning that each enzyme typically binds to only one particular substrate or a set of closely related substrates. This specificity is attributed to the unique shape of the active site, which often follows either a lock and key model or an induced fit model. In the latter, the active site can make minor adjustments to conform closely to the shape of the substrate, allowing the enzyme to catalyze a reaction with optimal efficiency. Despite the reaction taking place, enzymes are not consumed in the process; they remain unchanged and can bind to new substrate molecules afterward.