Describe the structures of DNA and RNA.

DNA (deoxyribose nucleic acid) is made of up two strands of nucleotides that are twisted together to make a double helix (twisted structure). Each nucleotide consists of nitrogenous bases and a backbone of deoxyribose sugars which are linked to phosphates by a phosphodiester bonds. (Insert labelled diagram of DNA structure)The nitrogenous bases come in two different forms: purines (adenine and guanine), which have a double ring structurepyrimidines (cytosine, thymine, uracil), which have a single ring structure. Tip for remember this: "Trying to remember adenine and guanine are purines is pure agony" DNA uses four of these bases: adenine, guanine, cytosine and thymine. These bases are responsible for connecting the two strands together since they are complementary to each other.Adenine links to thymine by 2 hydrogen bonds guanine links to cytosine by 3 hydrogen bonds.Tip for remember this: A-2-T and C-3-G. These form a 'zipper'-like connection between the two individual strands of nucleotides in DNA. The phosphodiester bond in each strand connects the carbon 5 (5') to carbon 3 (3') of the next nucleotide (recall chemical structure of carbon groups). This is important as the two strands run in opposite directions of each other - we call this antiparallel. The structure of RNA is slightly different to that of DNA. It is still composed of a nucleotide strand but the main differences are outlined below:Only a single strand of nucleotide in RNA compared to a double strand in DNA. This single strand in RNA can be looped back on itself to form base-pair regions. Ribose sugar in RNA instead of deoxyribose sugar in DNA RNA uses uracil instead of thymine in which is used by DNA.(insert labelled diagram of RNA structure)