What is DNA made of?
DNA is made of two long strands twisted into a double helix. Each strand is built from units called nucleotides, which contain a sugar, a phosphate group and one of four bases: A, T, C or G.
The four bases are adenine, thymine, cytosine and guanine. They pair up across the two strands in a specific way: A always pairs with T, and C always pairs with G. These base pairs are like the rungs of a twisted ladder, while sugar and phosphate form the sides. The order of the bases carries genetic instructions.
The human genome contains about 3 billion base pairs and around 20,000 protein-coding genes. If the DNA in one human cell were stretched out, it would be about 2 meters long. It is tightly packed into chromosomes inside the cell nucleus.
Discovering the double helix
James Watson and Francis Crick described the double helix structure in 1953, using X-ray images made by Rosalind Franklin and Raymond Gosling, along with data from Maurice Wilkins. Watson, Crick and Wilkins received the Nobel Prize in 1962. Franklin had died in 1958.
Did You Know?
Humans share about 99.9 percent of their DNA with each other, and around 98 to 99 percent with chimpanzees.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.