Final answer:
Centrifugation is used to separate the insoluble genomic DNA from pDNA and RNA in the solution after cell lysis. Enzymatic treatment with protease and RNAase follows, to degrade proteins and RNA respectively, leaving only plasmid DNA. Ethanol precipitation further purifies the plasmid DNA.
Step-by-step explanation:
After lysis of the bacterial cells during DNA extraction, the cell debris including the genomic DNA is typically insoluble. To separate this genomic DNA from the rest of the solution containing plasmid DNA (pDNA) and RNA, centrifugation is used. During centrifugation, the insoluble mass of genomic DNA, lipids, and proteins form a pellet at the bottom of the tube, while the soluble material, which includes the plasmid DNA and RNA, remains in the supernatant (liquid above the pellet). This supernatant is carefully transferred to a clean tube without disturbing the pellet.
Next, to purify the plasmid DNA from RNA, enzymatic treatment is performed using protease and RNAase. Protease degrades the proteins while RNAase specifically degrades RNA, leaving the plasmid DNA in the solution. Subsequently, ethanol precipitation is used to concentrate and purify the DNA even further. The plasmid DNA can then be collected and utilized for further analysis or experiments.