Enzymes (Updated)

Main Ideas

Enzymes are usually proteins that speed up chemical reactions, helping life processes happen efficiently. They can help build molecules or break them down.

Each enzyme has a specifically shaped active site where a matching molecule, called a substrate, can bind. When the substrate binds, the active site may adjust its shape to fit more closely. This is called induced fit.

The enzyme acts on the substrate to produce a product. Enzymes are catalysts: they can be used repeatedly and are not used up in the reaction.

Examples and Applications

Lactase breaks lactose—the sugar in milk, made of two sugar units—into smaller parts the body can digest. People who do not produce enough lactase may be lactose intolerant because they cannot break down lactose efficiently.

Digestive enzymes perform different jobs:

• Lipase breaks down fats, or lipids.
• Amylase breaks down starch.
• Protease breaks down proteins.

Enzymes may also need cofactors or coenzymes. These helpers can bind to the substrate or the enzyme’s active site and assist the enzyme in its work.

Enzymes have preferred pH and temperature ranges, which vary from one enzyme to another. If conditions move outside an enzyme’s suitable range, it may become denatured. Its shape changes, so it can no longer bind its substrate or work properly.

Because enzymes regulate many body processes, enzyme production—or a lack of particular enzymes—can be involved in diseases.

Speakers and Sources Featured

• Speaker: An Amoeba Sisters narrator; the individual speaker is not named in the subtitles.
• References used as analogies: Pac-Man and the Google Pac-Man Doodle. These are mentioned in the narration but are not additional speakers.