Deoxyribonucleic acid, better known as DNA, is a molecule that contains the genes that carry all of an organism’s genetic information.
It is highly complex and is made up of four types of bases called nucleotides, which are subsequently made up of three parts: a nitrogen base, a sugar called deoxyribose and a phosphate group.
The four kinds of bases are: thymine (T), adenine (A), guanine (G) and cytosine (C).
Adenine and guanine are known as puric or purine bases (a purine derivative) and cytosine and thymine are pyrimidic or pyrimidimes (a pyrimidine).
They are made of nitrogen, hydrogen, carbon and oxygen, except for adenine, which does not contain oxygen.
Bases are joined through hydrogen bridges in such a way that, chemically, adenine (A) can only get together with thymine (T), and guanine (G) can only get together with cytosine (C).
The first pair is connected by two hydrogen bridges and the second, by three.
DNA’s structure is made up of two stands or chains that twist over one another like a crooked staircase to form what’s known as the double helix.
Each strand has a backbone made of sugar and phosphate molecules, as well as four types of bases joined in pairs, forming a ladder.
These strands are anti-parallel (they run in opposite directions) and they cannot be separated without coming undone.
DNA replication
After discovering the structure of DNA and proving that it contained hereditary material, experts now had to determine how the molecule copied its information, in other words, how it replicated.
In 1953, James Warson and Francis Crick proposed the semi-conservative or bidirectional model, which states that the DNA double-helix splits its two strands and each one serves as a model to synthesize a new strand following the rules of DNA sequencing (guanine with cytosine and adenine with thymine) for nitrogen bases. In 1957, Matthew Meselson and Franklin W. Stahl confirmed this model using experiments.
Years later, other replication models where proposed: the conservative model and the dispersive model, but they have to be accepted.
