Base Pairs
DNA molecules form the basic building blocks of all known living organisms and, in respect to the human genome, which is collected on 23 chromosome pairs and determines the genetic make–up of an individual, there are some 3 billion DNA base pairs. Essentially, base pairs are molecules that link together strands of complementary DNA (deoxyribonucleic acid) or RNA (ribonucleic acid). DNA base pairs are either purines or pyrimidines and comprise four different bases: for purines, these are adenine and guanine; and for pyrimidines, these are cytosine and thymine. To make life more simple, adenine (purine) will always pair with thymine (pyrimidine) whilst guanine (purine) will always pair with cytosine (pyrimidine). In consideration of the structure of the DNA double helix, base pairs operate to link strands of DNA as rungs do on a ladder or as glue would between match sticks. In RNA, however, uracil replaces the thymine base, although the base pairs otherwise work in much the same way.
Base pairing is made possible by hydrogen bonding, which refers to the chemical process by which an electronegative atom bonds to a hydrogen atom which is covalently bonded to another electronegative atom. In the human genome, base pairs contribute to form up to 25,000 distinct genes, which effectively mark an individual with all his or her unique and inherited traits. DNA base pairs will only ever be connected in a sequence of adenine to thymine, and cytosine with guanine because these structures are the only kind that allow opportunities for hydrogen bonding to be established. These relationships are known as the Watson–Crick base pairing, which is derived from the scientists who identified the structure which lead to the DNA test as we know it today.
