Biomolecules

The body is built from a small set of molecule types. Nearly everything about how the body works comes down to what these molecules do.

The main classes

• Water — about 60% of body weight; the medium every reaction happens in, and a key player in temperature control.
• Proteins — the workhorses: they form structure, speed up reactions, carry cargo, and act as signals and receptors.
• Carbohydrates — the body’s quick fuel (glucose) and short-term energy store (glycogen).
• Lipids (fats) — long-term energy storage, the membranes that wrap every cell, and the raw material for steroid hormones.
• Nucleic acids — DNA stores the instructions; RNA carries them out.
• Minerals and ions — sodium, potassium, calcium, and others; small in quantity but essential for nerves, muscles, and bone.

Why it matters

Every organ system, every hormone, and every disease ultimately operates through these molecules. They are the vocabulary the rest of physiology is written in.