Editing Molecular biology (section)

===Gel electrophoresis===
[[File:SDS-PAGE.jpg|thumb|SDS-PAGE|left]]
{{main|Gel electrophoresis}}

Gel electrophoresis is a technique which separates molecules by their size using an agarose or polyacrylamide gel.<ref name="Lee-2012">{{Cite journal|last1=Lee|first1=Pei Yun|last2=Costumbrado|first2=John|last3=Hsu|first3=Chih-Yuan|last4=Kim|first4=Yong Hoon|date=2012-04-20|title=Agarose Gel Electrophoresis for the Separation of DNA Fragments|journal=Journal of Visualized Experiments|issue=62|pages=3923|doi=10.3791/3923|issn=1940-087X|pmc=4846332|pmid=22546956}}</ref> This technique is one of the principal tools of molecular biology. The basic principle is that DNA fragments can be separated by applying an electric current across the gel - because the DNA backbone contains negatively charged phosphate groups, the DNA will migrate through the agarose gel towards the positive end of the current.<ref name="Lee-2012" /> Proteins can also be separated on the basis of size using an [[SDS-PAGE]] gel, or on the basis of size and their [[electric charge]] by using what is known as a [[Two-dimensional gel electrophoresis|2D gel electrophoresis]].<ref>{{cite journal | vauthors = Lee PY, Costumbrado J, Hsu CY, Kim YH | title = Agarose gel electrophoresis for the separation of DNA fragments | journal = Journal of Visualized Experiments | issue = 62 | date = April 2012 | pmid = 22546956 | pmc = 4846332 | doi = 10.3791/3923 }}</ref>
[[File:Coomassie blue stained gel.png|thumb|Proteins stained on a PAGE gel using Coomassie blue dye]]