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DNA extraction is the process of isolating DNA from the cells of an organism isolated from a sample, typically a biological sample such as blood, saliva, or tissue. It involves breaking open the cells, removing proteins and other contaminants, and purifying the DNA so that it is free of other cellular components.
Centrifugation is the first step in most fractionations. Through low-speed centrifugation, cell debris may be removed, leaving a supernatant preserving the contents of the cell. Repeated centrifugation at progressively higher speeds will fractionate homogenates of cells into their components.
The different stages of the method are lyse, bind, wash, and elute. [1] [2] More specifically, this entails the lysis of target cells to release nucleic acids, selective binding of nucleic acid to a silica membrane, washing away particulates and inhibitors that are not bound to the silica membrane, and elution of the nucleic acid, with the end result being purified nucleic acid in an aqueous ...
Buoyant density of the majority of DNA is 1.7g/cm 3 [3] which is equal to the density of 6M CsCl solution. [citation needed] Buoyant density of DNA changes with its GC content. The term "satellite DNA" refers to small bands of repetitive DNA sequences with distinct base composition floating above (A+T rich) or below (G+C rich) the main ...
Centrifugation is a process that uses an electric motor to spin a vessel of fluid at high speed to make heavier components settle to the bottom of the vessel. Evaporation removes volatile liquids from non-volatile solutes, which cannot be done through filtration due to the small size of the substances.
Differential centrifugation, on the other hand, does not utilize a density gradient, and the centrifugation is taken in increasing speeds. The different centrifugation speeds often create separation into not more than two fractions, so the supernatant can be separated further in additional centrifugation steps.
A laboratory tabletop centrifuge. DNA is precipitated by first ensuring that the correct concentration of positive ions is present in solution (too much will result in a lot of salt co-precipitating with DNA, too little will result in incomplete DNA recovery) and then adding two to three volumes of at least 95% ethanol.
This mixture is then centrifuged. Because the phenol:chloroform mixture is immiscible with water, the centrifuge will cause two distinct phases to form: an upper aqueous phase, and a lower organic phase. The aqueous phase rises to the top because it is less dense than the organic phase containing the phenol:chloroform.