Each nucleotide is composed of one of four nitrogen-containing nucleobases ( cytosine, guanine, adenine or thymine ), a sugar called deoxyribose, and a phosphate group.
The two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Alongside proteins, lipids and complex carbohydrates ( polysaccharides), nucleic acids are one of the four major types of macromolecules that are essential for all known forms of life. DNA and ribonucleic acid (RNA) are nucleic acids. Deoxyribonucleic acid ( / d iː ˈ ɒ k s ɪ ˌ r aɪ b oʊ nj uː ˌ k l iː ɪ k, - ˌ k l eɪ-/ ( listen) DNA) is a molecule composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses.
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