WHAT IS DNA
The DNA is a long and complex molecule present in the cells of all living beings and it codifies in its structure all their specific characters that make every individual belong to a certain species and differ also from those of the same species.
DNA codifies also all the necessary informations to allow the biologic processes of every kind of cell and of the whole organism, like the synthesis of proteins, cellular reproduction, growth and death and their activity.

The name of this molecule is referred to its main structure; DNA is the abbreviation of Deoxyribonucleic Acid, given that it's basically formed by two very long polymeric chains wrapped the one around the other to form a double helix and formed by units of DESOXYRIBOSE, a simple sugar with 5 Carbon atoms and one -OH group less respect to the normal ribose.
The sugar units are tied one another by means of PHOSPHORIC GROUPS (-O-PO2H-O-).
The term "acid" is due to the two acid carboxylic groups (-COOH) at the extremities of each DNA chain.

The two chains are tied by means of molecular units, chemically bound to every helix and made by 4 different nitrogenated bases, named NUCLEOTIDES;
GUANINE, TYMINE, ADENINE, CYTOSINE, usually indicated shortly with the letters
G, T, A and C.

Every chain has a long series of these bases, all along it and every G of one helix can bind only a C base of the second helix, while an A can bind only a T of the other helix by means of HYDROGEN-BONDS, relatively weaker than normal intra-molecular bonds.
All these couples of bases create long sequences of nucleotides A-T and G-C that make the so-called GENETIC CODE of a living cell, containing all the detailed informations necessary to cellular life and reproduction and to the organism of which cells are part, when this is multicellular.

Every single genetic information that can fix a particular feature or biologic function is codified by a GENE that is a short segment of the DNA chain acting as a model for the fundamental process which the whole cellular life is based on:
the PROTEIN SYNTHESIS.
The genes sequence is always particular and constant in every DNA molecule of a particular type of cell.

Another fascinating and important feature of a DNA chain is that it can replicate itself exactly to reproduce the same GENOME or GENETIC HERITAGE, with the same sequence of billions of coupled bases, from a mother cell to all those it can generate by cellular division.
The DNA chain replicates

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