Salivary amylase is an enzyme found in the mouth. it speeds up the reaction of breaking down starch into sugars. why will salivary amylase only speed up the break down of carbohydrates and not protein? a) the enzyme is the wrong substrate for proteins. b) proteins will not fit into the active site of the amylase enzyme. c) proteins will never get broken down into smaller molecules like carbohydrates.

Ans.

Salivary amylase is a hydrolytic enzyme that speeds up the reaction of starch breakdown into simple sugars. Each enzyme is specific for a particular substrate and increases speed of a specific reaction because of active sites.  

Active site represents a region of enzyme, at which its substrate binds. The active site of salivary enzyme is specific for carbohydrates and can only binds with a carbohydrate (starch), not with protein. So, it cannot speed up the breakdown of a protein.

Thus, the correct answer is option (B). 'protein will not fit into the active site of salivary amylase.'