DNA stores instructions for cells — Science, 14–17 years
DNA is a long molecule whose sequence stores biological information. Cells read sections of it to help build proteins, while copying and small changes explain both inheritance and variation.
A sequence can be read
DNA is built from four chemical letters, usually written A, T, C and G. Their order forms instructions, much like letters in a sentence, but the instructions are for making and running a cell. A gene is one useful section of this DNA sequence.
The problem of making a new cell
When a cell divides, each new cell needs the same set of working instructions. DNA solves this storage problem because its sequence can be copied and passed on. It also explains family resemblance without requiring every feature to be copied perfectly.
From a gene to a protein
Suppose a short DNA section contains the bases A, T, G and C. The cell first makes a temporary RNA copy of the section, then reads the copy in groups of three bases. Each group helps choose an amino acid; a chain of amino acids folds into a protein. The sequence matters because changing one base can change a group.
A gene is not a finished trait
It is tempting to say that one gene simply equals one visible feature, because genes affect how cells work. In reality, many traits involve several genes and the environment can matter too. A gene usually contributes instructions or regulation; it does not write a person's whole appearance or behaviour by itself.
DNA in medicine and identification
DNA sequences help doctors identify some inherited disease risks and choose tests or treatments. Laboratories can also compare DNA patterns to help identify biological relatives or material from a crime scene. These uses require careful interpretation, because a match or risk is evidence, not a complete story.
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