Biology · Biomolecules · NEET
NCERT says the active site is a crevice or pocket into which the substrate fits. When the polypeptide chain of the enzyme folds on itself and criss-crosses, many pockets are made. One such pocket becomes the active site. The enzyme catalyses the reaction at a high rate through this active site.
An enzyme is a protein, so it has primary, secondary and tertiary structure. In the tertiary structure the chain folds upon itself and criss-crosses. This folding makes many crevices or pockets. One of these pockets is the active site. So the active site is created by the 3D folding of the protein, not by a separate part.
The active site has a special shape and chemical nature. Only a substrate whose shape matches this pocket can fit into it. Other molecules do not fit, so they are not acted upon. This exact fit between active site and substrate is the reason for substrate specificity.
The active site is a part of the enzyme (a pocket on the protein). The substrate is the reactant molecule that binds into that pocket. The active site stays on the enzyme; the substrate binds, is changed into product, and is released.
When the substrate binds to the active site, a temporary structure called the enzyme-substrate complex (ES complex) forms. In this bound state the active site breaks the chemical bonds of the substrate and converts it into product. Then the product leaves and the enzyme is free again.
Yes, in idea. The lock and key model explains that the substrate (key) fits only into a matching active site (lock). This picture explains why one enzyme acts on only one type of substrate. NCERT describes it simply as the substrate fitting into the pocket of the active site.
Regarding catalytic cycle of an enzyme action, select the correct sequential steps: A. Substrate enzyme complex formation. B. Free enzyme ready to bind with another substrate. C. Release of products. D. Chemical bonds of the substrate broken. E. Substrate binding to active site.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Substrate specificity means an enzyme acts on only one type of substrate (or one type of reaction). It happens because only the correct substrate fits into the enzyme's active site pocket.
Almost all enzymes are proteins and have active sites formed by folding. A few nucleic acids also act as enzymes; these are called ribozymes. For NEET, remember 'almost all enzymes are proteins.'
No. Binding is temporary. The substrate binds, is converted to product, and then the product is released, leaving the enzyme free to bind a new substrate molecule.
Enzymes are proteins, so high temperature (usually above 40C) denatures them and destroys the shape of the active site. Then the substrate can no longer fit and the enzyme stops working.
