Extraction+(Protein+purification)

**//What is the purpose of the technique? //**
 * Extraction (Protein purification): - **is isolation of a single type of protein from the hundreds of other proteins present in the cell in order to study protein function in vitro.

The purpose of the protein extraction is protein purification for analyzing biochemically in order to study the characteristics, function, structure and its existence in the cell. The process includes mechanical breakdown of the source of the protein ( animal or plant cell), separation of the cell material from the protein (purification), and the separation of the purified protein ion exchange column followed by size or molecular weight separation via size exclusion chromatography or by SDS-Page analysis (http:/wikipedia.org), or Affinity chromatography.

 To purify a protein, it must first be extracted from the cell or the tissue of plant or animal. This can be done in many different ways including osmotic shock, ultrasonic vibration, and mechanically using a blender or grounding. Homogenate or extract medium containing proteins and membrane-enclosed organelles with distinctive size, charge and density must be separated. **Figure 1** is showing a tube containing cell homogenate or extract with variation of size and density after mechanical breakdown of the cell. 

**Figure 2 ** is showing the preparative ultracentrifugation, which separates the homogenate or the extract medium by their size and density. It separates the homogenate or the extract medium into pellets, which is pushed into the bottom of the tube and the supernatant, which is the protein you want on the top of the tube. The centrifugation of the medium usually takes two to 1 to 3 repeated steps. 

There are three types of matrices used for protein chromatography: Ion-exchange; Gel-filtration, and Affinity chromatography. The best step to produce a very highly purified protein fractions and a more efficient procedure is affinity chromatography. Affinity chromatography uses an insoluble matrix that is covalently linked to a specific ligand, such as an antibody molecule that will directly bind to the specific protein. **Figure 3** shows the different types of chromatography utilized in protein purification. 

**//What are the origins of the technique? //** The origins of the extraction and purification of protein become possible 1940s, after the commercial development of an instrument known as the “preparative ultracentrifuge”, which rotates in high speed the homogenate or extract medium of the broken animal or plant cell (Alberts, Johnson, Lewis, Raff, Roberts, and Walter, 2008).

**References: ** **<span style="font-family: 'Times New Roman','serif';">Books: ** <span style="font-family: 'Times New Roman','serif';">Alberts, Johnson, Lewis, Raff, Roberts, and Walter, (2008). **<span style="font-family: 'Times New Roman','serif';">Websites: ** <span style="font-family: 'Times New Roman','serif';">[]