Question

Allosteric sites on an enzyme are:

• A. those other than drug-active sites
• B. those which change the shape of active sites
• C. those which don't change the shape of active sites
• D. all of the above

Answer 1

Answer: (A), (B)

The correct options are
A those which change the shape of active sites
B those other than drug-active sites

Some substances bind the enzyme at a site other than the active site. This other site is called the allosteric site. The allosteric site allows molecules to either activate or inhibit, or turn off, enzyme activity. These molecules bind the allosteric site and change the confirmation, or shape, of the enzyme.

Molecules that turn off enzymes are called allosteric inhibitors. Allosteric inhibitors change how the active site is shaped and prevents it from binding, or attaching, to the substrate.

Allosteric activators, on the other hand, make the enzyme more efficient. They change the shape of the enzyme, like allosteric inhibitors, but they make the enzyme better able to bind the substrate, instead of worse. This makes the enzyme do its job better.

Hence, the correct options are $\text{A}$ and $\text{B}$