Nucleotides and Nucleic Acids
Both DNA and RNA are known as nucleic acids. They have been given this name for the simple reason that they are made up of structures called nucleotides. Those nucleotides, themselves comprising a number of components, bond together to form the double-helix first discovered by the scientists James Watson and Francis Crick in 1956. This discovery won the two scientists the Nobel Prize. For now, when we discuss nucleic acids you should assume we are discussing DNA rather than RNA, unless otherwise specified.
A nucleotide consists of three things: A nitrogenous base, which can be either adenine, guanine, cytosine, or thymine (in the case of RNA, thymine is replaced by uracil). A five-carbon sugar, called deoxyribose because it is lacking an oxygen group on one of its carbons. One or more phosphate groups. The nitrogen bases are pyrimidine in structure and form a bond between their 1' nitrogen and the 1' -OH group of the deoxyribose. This type of bond is called a glycosidic bond. The phosphate group forms a bond with the deoxyribose sugar through an ester bond between one of its negatively charged oxygen groups and the 5' -OH of the sugar ().
Nucleotides join together through phosphodiester linkages between the 5' and 3' carbon atoms to form nucleic acids. The 3' -OH of the sugar group forms a bond with one of the negatively charged oxygens of the phosphate group attached to the 5' carbon of another sugar. When many of these nucleotide subunits combine, the result is the large single-stranded polynucleotide or nucleic acid, DNA ().