DNA

Deoxyribonucleic acid or DNA is the nucleic acid, containing the sugar deoxyribose, which forms the materials of which the chromosomes and genes of organisms are composed. It carries the blueprint for construction of all the cells of an organism and all instructions that control their activities, and which enables these instructions to be passed on from one generation to the next. DNA is found in all living organisms except certain viruses which contain RNA (ribonucleic acid), a closely related nucleic acid.

In eukaryotic ells- which make up the majority of organisms- DNA is found in the membrane bound sphere called the nucleus. Here, it forms chromosomes, normally long threads (but in cells that are about to divide chromosomes form separate X shapes as they duplicate themselves). Within the chromosomes DNA is tightly packed in coils and super coils. Once unraveled, DNA can be seen to consist of two long strands wound around each other in spiral structure or double helix, like a twisted ladder. The rungs of this ladder are made up of different bases. A rung is formed when adenine from one DNA strand binds with thymine on the other. The arrangement of bases along the double helix constitutes the genetic code, which controls production of the protein molecules that facilitate all cell activities, including metabolism and construction.