The chemical building blocks that keep cells alive
Living tissue contains small molecules such as sugars, amino acids and nucleotides, and large macromolecules built from them. Carbohydrates include monosaccharides like glucose, disaccharides like sucrose and polysaccharides like starch, glycogen and cellulose, joined by glycosidic bonds. Lipids include fatty acids, triglycerides and phospholipids; phospholipids form cell membranes. Proteins are chains of amino acids joined by peptide bonds, and their folded structure decides their function, from enzymes and antibodies to collagen and haemoglobin.
Enzymes are biological catalysts, mostly proteins, that lower activation energy. Each enzyme has an active site that fits its substrate, and its activity depends on temperature, pH and substrate concentration. Competitive inhibitors resemble the substrate and block the active site. Some enzymes need cofactors, such as metal ions or coenzymes like NAD. Nucleic acids, DNA and RNA, store and express genetic information. Metabolism is the sum of all chemical reactions in cells, with catabolic pathways breaking molecules down and anabolic pathways building them up.
Why it matters
Biomolecules explain nutrition labels, why we need protein and vitamins, and how lactose intolerance arises from missing enzymes. Enzymes are used in washing powders, cheese making and medical tests, and many drugs work by inhibiting specific enzymes. This topic underpins cell biology, physiology, genetics and biotechnology.
Key terms
- Macromolecule
- A large biological molecule such as a protein, polysaccharide or nucleic acid.
- Enzyme
- A biological catalyst that speeds up a specific chemical reaction in living cells.
- Active site
- The region of an enzyme where the substrate binds and the reaction occurs.
- Metabolism
- All the chemical reactions that take place within a living organism.