What is a gene? What is its chemical composition and function?

A gene is a functional unit of heredity that contains the instructions for building specific proteins or functional RNA molecules. Chemically, genes are composed of DNA (deoxyribonucleic acid), a double-stranded molecule made up of four nitrogen-containing bases—adenine (A), guanine (G), cytosine (C), and thymine (T)—linked to a sugar-phosphate backbone. Each gene represents a specific sequence of these bases that codes for a particular trait or protein, with the sequence determining the exact structure and function of the resulting protein.

The primary function of genes is to direct protein synthesis through a two-step process: transcription and translation. During transcription, the DNA sequence of a gene is copied into messenger RNA (mRNA), which then travels from the nucleus to ribosomes in the cytoplasm. There, during translation, the genetic code is read and amino acids are assembled in the correct sequence to form proteins. These proteins then carry out virtually all cellular functions—from catalyzing metabolic reactions as enzymes to providing structural support and regulating cellular processes. Genes also control inheritance, passing traits from parents to offspring, and determine the characteristics of organisms including physical appearance, metabolism, and susceptibility to certain diseases. This information storage and transfer capability makes genes the fundamental molecular basis of life and evolution.