When an enzyme is involved in a catabolic reaction A. its active site binds the substrates and changes shape, stressing the bond, lowering the activation energy, and breaking the bond. B. its active site binds the substrates and changes shape, bringing them close together, lowering the activation energy, and creating a bond. C. its active site binds the substrates and changes shape, stressing the bond, increasing the activation energy, and breaking the bond. D. its active site binds the substrates and changes shape, creating a bond by increasing the activation energy. E. None of the above.

Option-A

Explanation:

Enzymes are the protein molecules which speed up the chemical reaction in the organism and thus are known as the biocatalyst.

The enzymes are the tertiary structure of the proteins that is they are the globular form of the proteins. The globular structure contains an active site which is a pore-like structure to which the substrate molecules bind by forming a weak bond. This state is known as the transition stage which is higher in energy.

The formation of this transition state or enzyme-substrate complex lowers the threshold energy of reaction called activation energy and thus speed the reaction.

In the given question since the catabolic reaction involves the breaking of the bonds of the large molecules therefore the enzymes facilitate the breaking of the bond.

Thus, Option-A is the correct answer.