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Lesson: Chapter 1 — The Chemical Basis of Life

1.0 Introduction 5 of 5

The four biological molecules

A living cell contains thousands of organic compounds, but they can all be sorted into 4 main groups. These four groups are known as biological molecules.

1. Carbohydrates

Found in foods such as rice, bread and sugar, these are the main fuel that gives living things energy. Sugars, starch and cellulose belong to this group.

2. Proteins

Proteins form when small units called amino acids link together like a chain. Some proteins help the body's life processes as enzymes, hormones and antibodies. About 17% of an adult human body is protein.

3. Lipids

Oils and fats such as coconut oil and butter belong here. Their jobs are storing energy, building cell membranes and keeping the body warm.

4. Nucleic acids

These are DNA and RNA — the "instruction book" for building an organism. They hold genetic information and pass it from parents to their offspring.

Although these four groups are very different from one another, all of them are built mainly from the "four main elements" we met earlier: carbon (C), hydrogen (H), oxygen (O) and nitrogen (N).

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