The structure of DNA (deoxyribonucleic acid) consists of a phosphate group linked to sugar (deoxyribose), which itself is attached to one of the four nitrogen bases, A (adenine), C (cytosine), G (guanine) Timin). The phosphate-sugar-nitrogen group is a nucleotide. Nucleotides are linked together to form a DNA strand. Therefore, DNA is a nucleotide polymer. Two DNA strands interact with each other with nitrogenous bases forming a double-stranded DNA molecule. This molecule is similar to a scale in which phosphate-ribose groups make up amounts, and nitrogenous bases form columns. Two DNA strands on this scale are in the opposite orientation (antiparallel). This scale is twisted, giving the famous double-stranded double-stranded DNA. The distance between the two residues is 0.34 nm (0.34 x 10 -9 m). 1 coil of the spiral contains 10 base pairs (3.4 nm). The diameter of the DNA helix is 2 nm. The size of the human genome is 3.2 billion base pairs per haploid genome or 6.4 billion base pairs distributed over 23 pairs of chromosomes. Put an end to the end, it gives more than 2 meters of DNA per cell! In order to pack all this DNA into a nucleus, the DNA is strongly folded and compressed using proteins to form chromatin. Extreme DNA packaging forms mitotic chromosomes.

    Historically, nucleic acids (the so-called nuclein) were discovered by a Swiss biologist. The scientist discovered in the 1920s that nucleic acids were made from nucleotides, and showed that DNA is a carrier of genetic information. The double helix structure was discovered in 1953 by Nobel Prize winners.

    EXPERIENCE: There are many protocols for dna extraction from various living organisms. We are going to introduce 2 of them, one of the banana and the other of the epithelial cells of the oral cavity. These experiments do not require any specific equipment and can be carried out using products purchased in supermarkets. It should be noted that the obtained DNA does not have excellent quality. This would not allow for subtle experiments in molecular biology. DNA purification – DNA purified in this way is indeed still contaminated with other molecules (such as proteins) and probably partially destroyed by nucleases. However, these protocols make it easy to visualize your own DNA and evaluate the filamentous aspect of this molecule.

    A brief history of developments in the field of dna sequencing allows us to understand what some call the technological revolution … certainly, in the field of molecular biology, an innovation comparable to PCR. Pioneers of sequencing, developed two completely different methods for accessing reading sequences. They used selective chemical degradation strategies when one of them chose a selective enzymatic synthesis strategy. For these discoveries, scientists were awarded the Nobel Prize in Chemistry in 1980. In fact, this story only preserves one, since this strategy benefits from the invention of PCR. Also, the prices for chemistry and the development of capillary electrophoresis were not constrained, which allowed us to simplify the separation and analytical part.

    Being more and more effective, applications such as complete sequencing of higher eukaryotic genomes, metagenome approaches (must be cloned), transcriptional modulation studies (the SAGE method allowed them based on sequencing, this method is difficult and still requires the cloning phase) has almost known impassable limits (methods requiring too much time and capital). Take, for example, human genome sequencing projects using the dna kit. These projects will require more than 10 years of work and 300 million dollars for a private project and a little less than 3 billion dollars for a HUGO project.

    Note. The development of next-generation technologies (NGS) over the past 10 years is an unprecedented technological revolution. While sequencing a single human genome would require 10 years of international cooperation from 1993 to 2003 and $ 2.7 billion, it is now possible for several weeks, even several days, for costs of less than 1000 for the sequence of the entire coding region of 23 000 exome human genes representing 34 million DNA base pairs. Sequencing of entire human genomes for medical purposes (3 billion base pairs) has already been performed by several teams. This technological revolution lies at the heart of the medical revolution: exact or genomic medicine, the purpose of which is to optimize the diagnosis, prevention and treatment of human diseases in accordance with individual genetic variations.