1.2 Elements of Life - AP Biology (Updated 2025-2026)

Summary

Carbon and Organic Molecules

Carbon is central to life on Earth and forms the backbone of major biological macromolecules. Because a carbon atom can form four covalent bonds, it can connect with multiple atoms to build large, complex structures.

The study of carbon-containing compounds is called organic chemistry. In this lesson, organic molecules are described as molecules from living things that contain carbon atoms bonded to one another.

The Four Major Biological Macromolecules

The lesson introduces four major biological macromolecules: carbohydrates, proteins, lipids, and nucleic acids. These molecules are found across living things and will be explored further in the unit.

Macromolecule Elements Carbohydrates Carbon, hydrogen, and oxygen (CHO) Proteins Carbon, hydrogen, oxygen, nitrogen, and sulfur (CHONS) Lipids Primarily carbon, hydrogen, and oxygen; some also contain phosphorus Nucleic acids Carbon, hydrogen, oxygen, nitrogen, and phosphorus (CHONP)

• Carbohydrates: The name combines “carbon” with “hydrate,” referring to hydrogen and oxygen.
• Proteins: Sulfur can contribute to disulfide bridges.
• Lipids: Phospholipids, which contain phosphorus, are components of plasma membranes.
• Nucleic acids: DNA and RNA are built from nucleotides linked into chains.

Memory Aids and Next Topic

The instructor offers CHONS as a memory aid for proteins, CHOP for lipids, and CHONP for nucleic acids.

The next topic will cover how biomolecules are built up and broken down.

Speaker and Sources

• Speaker: Mr. Poser, the AP Biology teacher and presenter.
• Other named speakers or sources: None identified.