Enzymes are biological catalysts, which means they speed up chemical reactions without being consumed in the process. They are almost always proteins, though some RNA molecules can also act as enzymes (called ribozymes).

Here are some key features of enzymes:

* Highly specific: Each enzyme catalyzes a specific reaction or a small set of related reactions.

* Active site: Enzymes have a special region called the active site where the reaction takes place. This site is shaped to fit the specific molecule(s) it acts upon (called substrates).

* Lower activation energy: Enzymes lower the activation energy of a reaction, making it happen faster.

* Not consumed in the reaction: Enzymes are reusable.

Examples of enzymes:

* Amylase: Breaks down starch into sugars

* Lactase: Breaks down lactose (milk sugar)

* Pepsin: Breaks down proteins in the stomach

* DNA polymerase: Builds new DNA strands

Let me know if you have any other questions!