Molecular biology



Molecular biology is the study of biology on a molecular level including the structure, function, and makeup of biologically important molecules such as DNA, RNA, and proteins. Is the branch of biology that deals with the formation, structure, and function of macromolecules essential to life, such as nucleic acids and proteins, and especially with their role in cell replication and the transmission of genetic information.

The central dogma of molecular biology
The central dogma of molecular biology was first stated by Francis Crick in 1958 and re-stated in a paper published in the journal Nature in August, 1970. The central dogma of molecular biology states that "The DNA acts as a template to replicate itself, and is also transcribed into RNA, and the RNA is translated into protein." The central dogma states that once 'information' has passed into protein it cannot get out again. Transfer of information from protein to protein or from protein to nucleic acid is impossible. All cells, from the simplest bacteria to humans, express their genetic information in this way - a fundamental principle of this dogma. The finite automata below represents the central dogma:



There is special cases of transfers of biological sequential information. Reverse transcription, RNA replication and Direct translation from DNA to protein. The special transfers were indicated in the automata above (red arrows). In 1970 the first reports in Nature provided the first concrete evidence for the existence of transfer of information from RNA to DNA in retrovirus particles, the reverse transcription. The impact of this discovery changed in some way the central dogma of molecular biology accepted for which information transfer is unidirectional. This discovery led to the name change of the RNA tumor viruses to retroviruses. RNA replication is the copying of one RNA to another. Many viruses replicate this way. The enzymes that copy RNA to new RNA are called RNA-dependent RNA polymerases. A RNA virus need a RNA-dependent RNA polymerase to transcribe its genes into mRNA.

History
Molecular biology was created in the 1940s by researchers inspired by metaphorical concepts of code, language and information. In 1958, Francis Crick establishes the central dogma of molecular biology.

DNA sequencing
DNA sequencing is the determination of the complete or part of the nucleotide sequence of a specific molecule of DNA. This ability lies at the heart of the molecular biology revolution.

Gel Electrophoresis
Linear DNA molecules become separate according to size when subjected to an eletric field through a gel matrix. After electrophoresis is complete, the DNA molecules can be visualized by staining the gel with fluorescent dyes.

Copying DNA: Polymerase chain reaction (PCR)
One way to copy DNA in large quantities is the PCR (polymerase chain reaction) method. PCR amplifies a short DNA fragment and produces a great amount of identical strings. Single-target PCR is a robust and reliable technique for amplifying nucleic acids but it is still subject to many artifacts and environmental factors.

Southern blotting
Invented and named by Edwin Southern, this method is used for probing for the presence of a specific DNA sequence within a DNA sample. It is a common method of using gene probes for looking at similarities, or differences, in the structure of a gene.

Northern blotting
Is the simplest procedure to determine whether a gene is expressed in a sample but it really only confirm duplicate or greater differences in gene expression once the method is semi-quantitative.

Western blotting
Western blotting, also called immunoblotting is a method used to track specific proteins in cell-free extracts. Proteins are first separated according to size by SDS-PAGE. The fractioned proteins are tranferred to a sheet of a nitrocellulose membrane and then exposed to a specific antibody. Often, the antibodies are labeled with enzymes to allow detection.