Phenol extraction

Phenol extraction is a laboratory procedure which purifies nucleic acid samples using a phenol solution.

Phenol extraction may also refer to the process of extracting and isolating phenols from raw materials, such as coal tar. These purified phenols are used in many industrial and medical compounds and are used as precursors in some synthesis reactions.

Phenol extraction of nucleic acids
Phenol (C6H5OH) is a water-soluble compound consisting of a phenyl group (-C6H5) bonded to a hydroxyl group (-OH).

Phenol extraction is a technique often used to purify samples of nucleic acids from cells lysates.[1] To obtain nucleic acid samples, the cell must be lysed and the nucleic acids separated from all other cell materials.

Phenol is polar and has a higher density than water (1.07 g/cm3[2] compared to water’s 1.00 g/cm3). In a water-phenol solution, denatured proteins and other unwanted cell components dissolve in the phenol, while the polar nucleic acids dissolve in the water phase.[3] The solution is then centrifuged to separate the phenol and water into distinct organic and aqueous phases. The aqueous phase contains the purified nucleic acids, which can then be precipitated.

Phenol is often used in combination with chloroform.[4] Adding an equal volume of chloroform with phenol ensures a distinct separation between the aqueous and organic phases. Chloroform and phenol are miscible and mix to form a denser solution than phenol alone, therefore making the organic and aqueous layers more likely to separate and form distinct phases. This addition of chloroform is useful when the aqueous phase is being removed from the solution to obtain a purified nucleic acid sample.

The pH of the solution must be adjusted specifically for each type of extraction. Adjusting the pH to 7.0–8.0 is used for DNA extraction. The pH is adjusted to 4.5 for RNA specific extraction.At pH 4.5, hydrogen ions neutralize the negative charges on the phosphate groups, and cause the DNA to dissolve in the organic phase, allowing RNA to be isolated by itself in the aqueous phase.

See also

References
  1. Kirby, K. S. (1 Jul 1957). "A new method for the isolation of deoxyribonucleic acids: evidence on the nature of bonds between deoxyribonucleic acid and protein". Biochemical Journal. 66 (3): 495–504. doi:10.1042/bj0660495. ISSN 0264-6021. PMC 1200047. PMID 13459887.
  2. "Phenol". Sigma-Aldrich. Retrieved 9 Jul 2022.{{cite web}}: CS1 maint: url-status (link)
  3. Oswald, Nick (18 Oct 2021) [12 Feb 2008]. "The Basics: How Phenol Extraction of DNA Works". Bite Size Bio. Retrieved 9 Jul 2022.{{cite web}}: CS1 maint: url-status (link)
  4. Chan, P; Chan, D; To, K; Yu, M; Cheung, J; Cheng, A (May 2001). "Evaluation of extraction methods from paraffin wax embedded tissues for PCR amplification of human and viral DNA". Journal of Clinical Pathology. 54 (5): 401–403. doi:10.1136/jcp.54.5.401. ISSN 0021-9746. PMC 1731425. PMID 11328843.
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