Chemistry in Everyday Life

Lesson

Part 1 — how medicines work, chemically. (Formative assessment only; not in the board exam.)

In this lesson you will

Explain how drugs act on targets such as enzymes and receptors
Classify drugs by pharmacological effect and give examples
Describe antacids, antihistamines, tranquilisers, analgesics, antimicrobials and antifertility drugs
Distinguish antiseptics from disinfectants and bactericidal from bacteriostatic antibiotics

Table of everyday situations and the types of drug used
Situation	Type of drug
Acidity after a heavy meal	Antacid
Sneezing from pollen	Antihistamine
Headache	Analgesic
Throat infection	Antibiotic
Cleaning a cut	Antiseptic

Concept

Drugs and medicines

Drugs are chemicals of low molecular mass (about 100–500 u) that interact with macromolecular targets in the body and produce a biological response. When the response is therapeutic and useful, they are medicines, used to diagnose, prevent or treat disease. Most drugs are harmful at higher doses, so they are used only under medical supervision.

Table of the bases for classifying drugs with examples
Classification basis	Example of a class
Pharmacological effect	Analgesics (pain relief)
Action on a target	Antihistamines (block histamine)
Chemical structure	Sulphonamides
Molecular target	Drugs acting on enzymes or receptors

Diagram

Drugs that act on enzymes

Enzymes hold their substrate in an active site. A drug that is similar in shape to the substrate can occupy the active site instead: a competitive inhibitor. Some drugs bind elsewhere (an allosteric site) and change the shape of the active site. If the bond to the enzyme is strong and covalent, inhibition is irreversible.

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