The study of the structure and function of the large organic molecules associated with living organisms, especially the nucleic acids (DNA and RNA) and proteins.
Molecular biology is the study of biology at a molecular level. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interrelationship of DNA, RNA and protein synthesis and learning how these interactions are regulated.
Writing in Nature, William Astbury described molecular biology as:
"... not so much a technique as an approach, an approach from the viewpoint of the so-called basic sciences with the leading idea of searching below the large-scale manifestations of classical biology for the corresponding molecular plan. is predominantly three-dimensional and structural - which does not mean, however, that it is merely a refinement of morphology - it must at the same time inquire into genesis and function"
Relationship to other "molecular-scale" biological sciences
Researchers in molecular biology use specific techniques native to molecular biology (see Techniques section later in article), but increasingly combine these with techniques and ideas from genetics, biochemistry and biophysics. The central dogma of molecular biology where genetic material is transcribed into RNA and then translated into protein, despite being an oversimplified picture of molecular biology, still provides a good starting point for understanding the field.
Much of the work in molecular biology is quantitative, and recently much work has been done at the interface of molecular biology and computer science in bioinformatics and computational biology. As of the early 2000s, the study of gene structure and function, molecular genetics, has been amongst the most prominent sub-field of molecular biology.
Increasingly many other fields of biology focus on molecules, either directly studying their interactions in their own right such as in cell biology and developmental biology, or indirectly, where the techniques of molecular biology are used to infer historical attributes of populations or species, as in fields in evolutionary biology such as population genetics and phylogenetics.
Techniques of molecular biology
Since the late 1950s and early 1960s, molecular biologists have learned to characterize, isolate, and manipulate the molecular components of cells and organisms. RNA, a close relative of DNA whose functions range from serving as a temporary working copy of DNA to actual structural and enzymatic functions as well as a functional and structural part of the translational apparatus;
Expression cloning
One of the most basic techniques of molecular biology to study protein function is expression cloning. In this technique, DNA coding for a protein of interest is cloned (using PCR and/or restriction enzymes) into a plasmid (known as an expression vector). Introducing DNA into bacterial cells is called transformation, and can be completed with several methods, including electroporation, microinjection, passive uptake and conjugation. Introducing DNA into eukaryotic cells, such as animal cells, is called transfection.
In either case, DNA coding for a protein of interest is now inside a cell, and the protein can now be expressed. The protein can be tested for enzymatic activity under a variety of situations, the protein may be crystallized so its tertiary structure can be studied, or, in the pharmaceutical industry, the activity of new drugs against the protein can be studied.
Polymerase chain reaction (PCR)
The polymerase chain reaction is an extremely versatile technique for copying DNA. For example, PCR can be used to introduce restriction enzyme sites, or to mutate (change) particular bases of DNA.
Gel electrophoresis
Gel electrophoresis is one of the principal tools of molecular biology. The basic principle is that DNA, RNA, and proteins can all be separated using an electric field. In agarose gel electrophoresis, DNA and RNA can be separated based on size by running the DNA through an agarose gel.
Southern blotting
Named after its inventor, biologist Edwin Southern, the Southern blot is method for probing for the presence of a specific DNA sequence within a DNA sample. DNA samples before or after restriction enzyme digestion are separated by gel electrophoresis and then transferred to a membrane by blotting via capilliary action. The membrane can then be probed using a DNA probe labeled using a complement of the sequence of interest. Southern blotting is less commonly used in laboratory science due to the capacity of using PCR to detect specific DNA sequences from DNA samples.
Northern blotting
The Northern blot is used to study the expression patterns a specific type of RNA molecule as relative comparison among of a set of different samples of RNA.
Western Blotting
Antibodies to most proteins can be created by injecting small amounts of the protein into an animal such as a mouse, rabbit, sheep, or donkey (polyclonal antibodies)or produced in cell culture (monoclonal antibodies).
In Western blotting, proteins are first separated by size, in a thin gel sandwiched between two glass plates in a technique known as SDS-PAGE (for Sodium Dodecyl Sulphate Poly-Acrylamide Gel Electrophoresis).
Analogous methods to western blotting can also be used to directly stain specific proteins in cells and tissue sections. However, these immunostaining methods are typically more associated with cell biology than molecular biology.
The terms "Western" and "Northern" are jokes: The first blots were with DNA, and since they were done by Ed Southern, they came to be known as Southerns.
Abandoned Technology
As new procedures and technology become available, the older technology is rapidly abandoned.
History
Molecular biology was established in the 1930s, the term was first coined by Warren Weaver in 1938 however. Warren was director of Natural Sciences for the Rockefeller Foundation at the time and believed that biology was about to undergo a period of significant change given recent advances in fields such as X-ray crystallography. Watson Maurice Wilkins Erwin Chargaff Rosalind Franklin Max Perutz Susumu Tonegawa Christiane Nüsslein-Volhard Frederick Sanger Francois Jacob
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