The zymogen is an inactive precursor of an active enzyme.

Enzymes are proteins that act as biological catalysts to speed up chemical reactions. The molecules that enzymes act on are called substrates, and the enzyme converts the substrates into different molecules called products. Here are some examples of enzymes and their functions: Lipases: Help digest fats in the gut Amylase: Helps change starches into sugars in the saliva. Amylase is present in human saliva and certain other mammals. It helps digest foods, such as potatoes and rice, that contain large amounts of starch. Maltase: Breaks the sugar maltose into glucose. Maltase is found in... Show more

Enzymes are proteins that act as biological catalysts to speed up chemical reactions. The molecules that enzymes act on are called substrates, and the enzyme converts the substrates into different molecules called products.

Here are some examples of enzymes and their functions:
Lipases: Help digest fats in the gut
Amylase: Helps change starches into sugars in the saliva. Amylase is present in human saliva and certain other mammals. It helps digest foods, such as potatoes and rice, that contain large amounts of starch.
Maltase: Breaks the sugar maltose into glucose. Maltase is found in plants, bacteria, and yeast. In humans and other vertebrates, it is thought to be synthesized by cells of the mucous membrane lining the intestinal wall.
Trypsin: Breaks proteins down into amino acids in the small intestine 

Enzymes are also present in microbes, where they help digest and utilize fractions of organic matter. 
Enzymes are compartmentalized, which means that enzymes needed for specific processes can be kept in the places where they act. This ensures that they can find their substrates readily, don't damage the cell, and have the right microenvironment to work well.

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