DNA is easily degraded by nucleases (enzymatic proteins), so DNA-protein interactions during DNA isolation must be limited. If the sample is kept on ice, protein activity drops to zero, so even if nucleases are present, they cannot act on and degrade the DNA.
The ice bath is an indirect method for protecting the DNA until you can separate the proteins from the DNA.What is the function of an ice bath in protein precipitation in DNA isolation?
There are three basic steps in a DNA extraction, the details of which may vary depending on the type of sample and any substances that may interfere with the extraction and subsequent analysis.
Break open cells by grinding or sonication, and remove membrane lipids by adding a detergent.
Remove cellular and histone proteins bound to the DNA, by adding a protease, by precipitation with sodium or ammonium acetate, or by using a phenol/chloroform extraction step.
Precipitate DNA in cold ethanol or isopropanol, DNA is insoluble in alcohol and clings together; this step also removes salts.
Smaller DNA molecules may require incubating at lower temperatures for as long as overnight for efficient precipitation.
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