See also: BM
The molecular biology (BM) is a scientific Discipline with the crossing of the Génétique, Biochimie and Physique, whose object is the comprehension of the mechanisms of operation of the cell at the molecular level. The term “molecular biology” also indicates the whole of the techniques of handling of nucleic acids (DNA, ARN), called so technical of genetic Engineering.
One shortens the expression molecular biology in " bio mol" or " BM".
Molecular biology appeared at the 20th century, following the development of the laws of the genetics, the discovery of the Chromosome S and the identification of the DNA like chemical support of genetic information.
After the discovery of the structure in double helix of the DNA in 1953 by James Watson (1928 -), Francis Crick (1916 - 2004), Maurice Wilkins (1916 - 2004) and Rosalind Franklin (1920 - 1958) molecular biology experienced important developments to become a tool impossible to circumvent of modern biology starting from the Années 1970.
Relationship to other biological sciences with " the scale moléculaire"
The researchers in molecular biology use specific techniques for molecular biology (see further Techniques from molecular biology ), but combine them more and more with the techniques and the ideas coming from the Génétique and the Biochimie. There is no border well defined between these disciplines, although there was at a certain time. The figure opposite illustrates a possible sight of the relation between the fields:
the biochemistry is the study of the chemical substances and the vital processes which occur in the living organisms.
- the genetic is the study of the effects of the genetic differences between the organizations. Often that can be deduced by the absence from a normal component (for example a Gène). The study of the " mutant " – organizations of which it misses one or more functional components compared to supposedly the " Standard naturalness " or with the normal Phenotype. The genetic interactions such as the epistasy S often put at fault simple interpretations of these studies by " élimination".
- the molecular biology is the study of the processes of replication, transcription and translation of the Genetic material. The central Dogme of molecular biology where the genetic material is transcribed in ARN, then translated into proteins, although it is a very simplified image of molecular biology, still provides a good starting point to include/understand this field. This image, however, must be revised in the light of the new roles which one discovers with ARN.
The essence of work in molecular biology is quantitative, and recently many work were done with the intersection molecular biology and data processing, in the Bio-data processing and the calculative Biologie. Since the years 2000, the study of the structure and function of genes, the molecular Genetic , belonged to the most projecting under-fields of molecular biology.
More and more, of many other fields of biology concentrate on the molecules, either directly, by studying their own interactions as in cellular Biologie and Biologie of the development, or indirectly, when the techniques of molecular biology are used to deduce the historical attributes from the Population S or the Espèce S, as in the fields of the biology of the evolution such as the Génétique of the populations and the Phylogénie. There is also a long tradition of study of the Biomolécule S " starting from the bas" in Biophysics.
Techniques of molecular biology
Since the end of the year 1950 and the beginning of the year 1960, the molecular biologists learned how to characterize, insulate and handle the molecular components of the cells and the organizations. These components include DNA, carrier data genetic, ARN, near to the DNA whose functions go from the provisional copy of DNA until the real structural and enzymatic functions and who is a part functional and structural of the apparatus traductionnel, and the Protéine S, structural Molécule S is enzymatic most important of the cells.
Cloning of expressionsOne of the most elementary techniques in molecular biology to study the role of proteins is the cloning of expressions. In this technique, the DNA coding the protein which interests us is clone by using the Chain reaction by polymerase (PCR in English for Polymerase Chain Reaction ) and/or of the enzymes of restriction in a Plasmide (which one calls vector of expression). This plasmide can have elements of sequences special promotrices to direct the production of protein in question and can also have markers of antibiotic resistance to help to follow the plasmide.
This plasmide can be inserted in cells, either of bacterium, or of animal. To introduce DNA into bacterial cells is called transformation, and that can be supplemented several manners: electroporation, Microinjection, passive consumption and conjugation. To introduce DNA into cells of eucaryotes, such as animal cells, is called Transfection. Several techniques different of transfection are available: transfection calcium phosphates, Transfection of liposomes, reagents of transfection owners such as Fugene. The DNA can then be introduced into the cells by using viruses or pathogenic bacteria as conveyers. In such cases, the technique is called viral/bacterial transduction, and the cells are known as transduites.
In both cases, coding DNA for the protein which interests us is now inside a cell, and the protein can be now expressed. A variety of systems, such as inductibles promoters and specific factors announcing the cells, are available to help the protein which interests us to be expressed with high level. Great quantities of proteins can then be extracted the bacterial cell or eucaryote. The protein can be tested to know its enzymatic activity in a variety of situations, it can be crystallized so that one can study his tertiary structure, or, in the drug company, one can study the activity of new drugs on protein in question.
Chain reaction by polymerase
See also: Chain reaction by polymerase
The Chain reaction by polymerase (English PCR, for Polymerase Chain Reaction ) is an extremely flexible technique of copy of DNA. Approximately, the PCR makes it possible a simple sequence of DNA to be copied million times, or to be faded by predetermined means. For example, the PCR can be used to introduce sites of enzymes of restriction, or to transfer (to change) particular bases of the DNA. The PCR can also be used to determine if a particular fragment of DNA is in a Bibliothèque of DNA complementary. The PCR has many variations, like the PCR with transcription reversed (English RT-PCR for Reverse Transcription Polymerase Chain Reaction ) for the amplification of the ARN, and, more recently, the PCR real-time (qPCR) which allows quantitative measurements of molecules of DNA and ARN.
See also: Electrophoresis
The electrophoresis is one of the principal tools of molecular biology. The basic principle and that the DNA, the ARN and the proteins can be separated by electric fields. In the electrophoresis in Freezing of agarose, the DNA and the ARN can be separate according to their size while making circulate the DNA through a gel of agarose. The proteins can be separate according to their size by using a gel SDS-PAGE. The proteins can also be separated by their electric Charge, by using what is called an isoelectric gel.
See also: Southern blot
Named thus according to the name of his inventor, the biologist Edwin Southern, the Southern blot is a method to probe the presence of a precise sequence of DNA inside a sample of DNA. Samples of DNA before or after digestion by a Enzyme of restriction are separated by electrophoresis and are transferred on a membrane by marking via capillary action. The membrane can then be tested by using a probe DNA marked with a complement of the sequence in question. In the beginning, the majority of the protocols used radioactive markers; however, now, there exist possibilities of nonradioactive markings. Southern blot is less often used in the laboratories, owing to the fact that PCR already makes it possible to detect specific sequences DNA starting from samples of DNA. However, these markings are still used for certain applications, such as the measurement of the number of copies Transgénique S in the transgenic mice, or in the engineering of lines of embryonic Original cells to invalidated genes.
See also: Northern blot
The Northern blot is used to study the models of expression of a specific type of molecule of ARN in relative comparison with a whole of various samples of ARN. It is primarily a combination of a denaturation of electrophoresis of ARN, and of a blot . In this process, the ARN is separate according to the size, then is transferred on a membrane which is then probed with a complement marked for the interesting sequence. The results can be visualized of a variety in ways according to marking used; however, the majority lead to a revelation of bands representing the size of the ARN detected in the sample. The intensity of these bands is related to the quantity of ARN targeted in the analyzed samples. The process is generally used to study when and how much gene expressions occur by measuring the quantity of this ARN present in the various samples. It is one of the most fundamental tools to determine when certain genes are expressed in living tissue.
See also: Western blot
Separation of proteins by electrophoresis SDS-PAGE only according to their size (SDS_sodium dodécylsulfate_ denatures the structures tertiary sector and quaternary proteins and the loads all negatively), then transfer of proteins separated on membrane to make them available to various immunological or different markings.
The antibodies for the majority of proteins can be created by injection of minor amounts in the animals such as the mouse, rabbit, the sheep or the ass (antibodies polyclonaux) or produced in a culture of cells (monoclonal antibodies). These antibodies can be used in a variety of analytical techniques and preparations.
In the Western blot (immunobuvardage), the proteins are initially separate according to their size, in a fine gel taken between two glass plates by a technique which one calls SDS-PAGE (for Sodium Dodecyl Sulfate Poly-Acrylamide Freezing Electrophoresis ). The proteins in freezing are then transferred on a PVDF, nitrocellulose, nylon or another membrane of support. This membrane can then be probed with solutions of antibody. The antibodies which stick specifically to protein in question can then be visualized according to a variety of techniques, of which colorimetry, the Chimiluminescence or the Autoradiographie.
Similar methods of Western blot can also be used to directly mark specific proteins in cell S and sections of fabrics. However, these methods of immunological markings are rather associated with the cellular Biologie that with molecular biology.
The " terms; Western" and " Northern" are word games: the first blots were on the DNA, and as they were made by Edwin Southern, they took the name of " Southern" ( southern wants to say " sud" in English; while western means " ouest" and northern , " nord"). It is not very probable that Patricia Thomas, inventeuse of the blot ARN, which became the Northern blot , uses really this term. To push the joke further, one can find, in the literature, from the references towards south-weesterns (" south-ouest") (interactions protein-DNA) and of the far-westerns (of the " far-ouest") (interactions protein-protein).
Chip with DNA
See also: Chip with DNA
A chip with DNA is a collection small spots connected to a solid support such as a Lame of microscope; each spot contains one or more Molécule S of DNA. The chips make it possible to gather a great number of tiny spots (of a diameter of 100 microns) on a simple blade; if each spot contains a molecule of DNA corresponding to complementary to simple a Gène, one can analyze, in an organization, the genetic Expression of each gene in only one experimentation. For example, the common Yeast of baker, Saccharomyces cerevisiae , contain approximately 7000 genes; with a chip with DNA, one can measure quantitatively how each gene is expressed, and how its expression changes, for example, when the temperature is changed.
There are several different manners to manufacture chips with DNA; most current are the chips with silicon, blades of microscope whose spots are 100 microns in diameter, the chips which one can adapt to his needs, and those with larger spots on porous membranes (macropuces).
The chips can also be manufactured for molecules other than the DNA. For example, a chip with Anticorps can be used to determine which Protéine or Bactérie is present in a sample of blood.
Abandoned technologyAs new procedures and new technologies became available, the old ones are quickly abandoned. Typical examples are the methods to determine the size of the molecules of DNA. Before the electrophoresis, with agarose and polyacrylamide, one calculated the size of the DNA by sedimentation in sweetened gradients, a slow and hard technology requiring an expensive instrumentation; and before the sweetened gradients, one used the viscometry.
Independently of their historical interest, it is interesting to know the old techniques because that can be useful to solve particular problems.
HistoryMolecular biology appeared in the years 1930, the term having however been invented only in 1938 by Warren Weaver. Warren Weaver was at the time director of the Natural science for the Fondation Rockefeller and thought that biology was on the point of living one period of significant changes being given the recent projections in the fields such as the Diffractométrie of x-rays. He thus invested important sums coming from the Rockefeller Institute in the biological fields.
List few known molecular biologists
- Francis Crick
- James D. Watson
- Maurice Wilkins
- Erwin Chargaff
- Franklin Rosalind
- max Perutz
- Susumu Tonegawa
- Christiane Nüsslein-Volhard
- Frederick Sanger
- François Jacob
- Jacques Monod
- “It was once… the DNA”: an educational site on the basis of traditional and molecular genetics
- Doctoral School Molecular biology, Intégrative and Cellulaire (BMIC), Lyon (FRANCE)
|Random links:||Sistema inquisitorial | Thomas Abbt | Francine Ruel | State binational | Marlon Devonish | Presidential election of the United States of America 1968|