DNA

DNA Structure Deoxyribonucleic acid (DNA) is a polynucleotide (a molecule composed of a chain of nucleotides). Each nucleotide consists of: a nitrogen base (adenine, thymine, guanine, or cytosine) a sugar (deoxyribose) a phosphate group

A molecule of DNA is composed of two polynucleotide chains held together by Hydrogen bonds between the bases. Phosphodiester (covalent) bonds hold each sugar to the phosphate of the adjacent nucleotide. In DNA, adenine always bonds with thymine with 2 H bonds, and cytosine always bonds to guanine with 3 H bonds.

The Orientation of the two chains is Opposite, to account for the Hydrogen bonding of Oxygen and Hydrogen atoms, respectively.

James Watson and Francis Crick discovered the structure of DNA in 1953 They won the Nobel prize with Maurice Wilkins in 1962

Rosalind Franklin’s work in x-ray crystallography was critical in revealing the structure of the DNA molecule. The "cross" formed of dark spots indicated that the molecule had a helical structure.

DNA has coding regions known as genes that determine the characteristics of an organism. An alteration in the DNA sequence is known as a mutation. Mutations may be caused by chemical agents, ultraviolet radiation, or natural causes (e.g. viruses). Mutations can also occur during the process of DNA replication.

DNA Replication The structure of DNA allows it to be easily replicated (copied). The DNA molecule “unzips” and each side serves as a template. On each half of the molecule, a new complementary half is built. The two new DNA molecules are identical to each other.