Exon-intron structure of genes and DNA, illustration. The double helix of the genetic molecule deoxyribonucleic acid (DNA) consists of sections called genes. A gene (large bracket label) is a sequence of nucleotides that encodes the formation of a particular protein. Genes themselves consist of sections called exons and introns. The exons (one at left and one at right) are the expressed part of the DNA, while the introns (one between the exons) are non-coding regions that are spliced (removed) during transcription. DNA is the genetic material that controls the growth and development of all living organisms. It is a double helix, with two spiralling sugar phosphate strands joined by nucleotide base pairs (coloured bars). The order of these nucleotides base pairs forms the genetic code. For this illustration with labels, see image C046/9216.