You may extract RNA using one of the two methods namely, phenol-chloroform based extraction or extraction using commercially available silica spin column kits.
Phenol-chloroform based RNA extraction relies on the use of acid guanidinium thiocyanate-phenol-chloroform to promote phase separation of biological mixtures and subsequent selective isolation of molecules of interest. On the other hand commercially available column-based kits are often more straightforward but can be relatively expensive compared to phenol-chloroform extraction methods.
Phenol-chloroform based RNA extraction is advantageous when one has to extract RNA from small quantities of cells or tissues because it yields more RNA than silica column-based protocols. For phenol-chloroform based RNA extraction you may use proprietary phenol-based reagents like TRIzol which is generally more economical, but significant contaminants including phenol, guanidine, chloroform, and salt may remain in the samples. To overcome the issue of RNA contamination in the phenol-chloroform based RNA extraction method, you may add an additional chloroform step and several subsequent RNA washing steps using 75% ethanol.
Some of the reagents and their uses.
Lysis buffer: This will help to break the cell membrane and facilitate the RNA release. This is typically TRIzol, phenol, or CTAB buffers.
Chloroform: This is a reagent generally used for polysaccharide removal. Some protocols suggest performing two washes with chloroform for better results.
Isopropyl alcohol: This reagent facilitates protein removal.
You may refer to the protocol provided in the article attached below. It may be helpful!
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I have done RNA isolation from different types of tissue i(n the time when no RNA isolation kits were available) with the method described by Chomczynski and Sacchi, 1987 (attached). I am not sure if the purchase of all components required is cheeper than a comercial kit but this might be dependent on the number of samples you need to process.