DNA

DNA

DNA

Introduction

DNA stands for deoxyribonucleic acid. This is the molecule of heredity. It contains in coded form all information related to the life of a living organism, from simple to more complex animal, plant, bacterial, viral. (Alberts, 1999) In general after the figures and examples, unless otherwise stated, are those of the human body.

Structure of nucleotide

Nucleotides are organic molecules formed by the covalent attachment of a five-carbon monosaccharide (pentose), a nitrogenous base and a phosphate group. The monomers of nucleic acids (DNA and RNA) which form linear chains of thousands or millions of nucleotides, but also perform important functions such as free molecules (e.g. ATP).

Each nucleotide is an assembly of three components:

Fig. 1 Nitrogenous bases: compounds derived from purine and pyrimidine heterocyclic aromatic.

It was already known that DNA molecules are long chains of organic compounds called nucleotides, and each link contains sugar nucleotide, a phosphate, and one of four nitrogenous bases: adenine (A), thymine (T), guanine (G) or cytosine (C), however, still had to determine how substances are combined to create a DNA molecule, a task that took several European and U.S. laboratories. In early 1953, both in London and Cambridge was clear that the DNA would be a double helix, as Watson and Crick had established, the phosphate groups form, by its outer side, the support structure and nucleotides would look toward the center (Bray, 2007).

Base-pair rules

The structural links of the nucleic acids are nucleotides, which are compounds derived from the union of a nitrogenous base, a pentose and phosphoric acid (phosphate).

The nitrogenous bases are of two types according to their origin:

The purine (purine bases): adenine (A) and guanine (G).

The pyrimidine (pyrimidine bases), cytosine (C), Uracil (U) and thymine (T).

Fig. 2

The nucleosides are formed by the union of a base with a pentose (ribose or deoxyribose). Carbon 1 of the pentose is attached to a nitrogen atom of the nitrogenous base through an N-glycosidic bond. Depending on the pentose which joins the nitrogenous base, the nucleoside will be grouped into: ribonucleoside (containing ribose) and Deoxyribonucleosides (with 2-deoxyribose) (Bray, 2007).

Process of replication, including enzyme function

In almost all cellular organisms, replication of DNA molecules occurs in the nucleus, just before cell division. It begins with the separation of the two polynucleotide chains, each of which then acts as a template for the assembly of a new complementary strand. As the original string is opened, each of the nucleotides of the two resulting strings complementary nucleotide attracts another previously formed by the cell (Bray, 2007). The nucleotides are joined together by hydrogen bonds to form the rungs of a new DNA molecule. As the complementary nucleotides are fitting into place, enzyme called DNA polymerase binds the phosphate group linking of a sugar molecule to the next, in order to build the thread side of the new DNA molecule. This process continues until it has formed a new polynucleotide chain along the old, is being rebuilt and a new molecule with double-helix ...