Bases

Nucleobases

From Human Genome Project, the genomic bases are: adenine (A), thymine (T), guanine (G) and cytosine (C). There is a fifth base, Uracil (which replaces Thymine when converting DNA into RNA).

The chemical structure is given as follows:

Note that the “purines” (A, G) have a two-ring structure, while “pyrimidines” (C, T, U) have just a single ring.

Pairing

Since DNA is stranded (double-helix), complementary bases pair as follows:

Here is a depiction of what is happening chemically when the bases pair:

Left: Cytosine pairs with Guanine; Right: Adenine pairs with Uracil. By Iquo - Illustrated by the uploader, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1042812

TODO: see here for more information about 5’ and 3’ - has to do with where the phospate attaches.