We can consider the DNA or deoxyribonucleic acid, such as the brain) ~ cell that regulates the number and nature of each type of structure and cellular composition,ansmitting hereditary information and determining the structure of proteins by enzymes that determine the remainder of cellular functions.

At the end of last century was also discovered the existence of a second class of nucleic acid called ribonucleic acid (RNA). The RNA is found both in the core (specifically in the nucleolus) and in the cytoplasm of cells abundantly.

Both types of nucleic acid, DNA and RNA, are simultaneously in eukaryotes (cells with distinct nucleus) and prokaryotes (bacteria, etc.). And only one in the
virus.

COMPOSITION OF NUCLEIC ACIDS

The nucleic acids of high molecular weight polymers consisting of elementary units called nucleotides ~), which consist of three components:

1. Sugar molecule

ð Ribose, in the case of RNA

ð Deoxyribose in DNA case

2. Nitrogenous organic base

ð adenine, guanine (purine bases), cytosine and thymine (pyrimidine bases) in
the case of DNA.

ð adenine, guanine (purine bases), cytosine and uracil (pyrimidine bases) in the
case of RNA.

3. Phosphate groups

The nucleotides are joined into chains whose skeleton is formed by the union of one nucleotide sugar and phosphate of the next, leaving the nitrogen bases in
the central part, each attached to C1 of sugar. These bases are those that yield specific nucleic acid.

STRUCTURE OF DNA

Primary Structure

The primary structure is given by the nucleotide sequence. When you want to represent the sequence of an oligonucleotide or a nucleic acid, is represented by the terminology of each of the bases. For example:

ATCCCAGCCCGATTAAAGCC-5′-3 ‘

This sequence represents an oligonucleotide with 20 bases, of which 6 are adenine (A), 3 are thymine (T), 8 are cytosine (C) and 3 guanine (G).

The order of the sequence is very important since it lies in the information contained in the nucleic acid, the guidance is given in the sense 5 ‘to 3′ or 3 ‘to 5′ 5 ‘represents the terminal end of the phosphate and 3′ the tail end of
the carbon atom of the deoxyribose.

Secondary structure

Edwin Chargaff analyzed the DNA bases found by hromatographic methods, they are not in the same proportion and the number of adenines is equal to thymine and
cytosine, guanine at.

In 1953 James Watson and Francis Crick built a three-dimensional model of DNA with the most energetically favorable configuration combining the data obtained
so far on it, Chargaff’s findings and interpretation of the spectra of
three-dimensional X-ray diffraction, the latter was of great importance for the achievement of such a model, which consists of an antiparallel double helix whose basic skeleton consists of the sugar-phosphate chains, leaving the central part the bases, the odds of a string with the other complementary and forming
hydrogen bonds among themselves, a factor that gives stability to the double helix. The clash of bases is constant always adenine with thymine and facing each other are formed two hydrogen bonds, and guanine to cytosine, forming
between the two three hydrogen bonds. This feature causes the two strands are complementary. The two strands of the double helix have opposite directions,
while one goes in the 5 ‘to 3′ and the other does so in effect 3 ‘to 5′. Why we speak of DNA as an antiparallel double helix.

Layout of the union between bases forming two hydrogen bonds between adenine-thymine and three hydrogen bonds between cytosine – guanine.

Double helix structure of DNA right.

Tertiary and quaternary structures

Given that the length of a strand of human DNA is several eters, due to adopt other structures need to be inside the cell. These structures, tertiary and quaternary, allow the packing of DNA forming the chromosomes. In eukaryotic cells there are several chromosomes and in prokaryotes, there is a known DNA
packaging seudocromosoma.