You crack your cells open and carry out a miniprep, trying very hard not to get any contaminating genomic DNA in your sample.
Isolation of plasmid DNA and analysis of isolated plasmid. Introduction: A plasmid is an autonomously replicating extra-chromosomal genetic element. In other words, this is a DNA molecule external to the bacterial chromosome that is able to replicate on its own and distribute its daughter molecules to daughter cells. You have successfully cloned a fragment of chromosomal DNA containing a tetracycline resistance cassette into a plasmid (pET11a). To this end you have (1) isolated total chromosomal DNA from your assigned bacterial strain and digested this DNA with the restriction enzyme BamHI. To this end you will digest 10 uL of the isolated plasmid with restriction enzyme BamHI. The 40 uL of the plasmid DNA will be quantified using Nanodrop spectro-photometry. A predetermined amount of the DNA will be submitted for sequence analysis. There are several methods to isolate plasmid DNA from bacteria, the archetypes of which are the miniprep and the maxiprep / bulkprep. The former can be used to quickly find out whether the plasmid is correct in any of several bacterial clones.  Almost all plasmids are circular. They contain a small number of genes, which can include genes that make cells resistant to antibiotics. Plasmids are used extensively in cloning DNA. You insert some foreign DNA into the plasmid DNA, and then infect cells with the DNA in a process called transformation. There are several ways to purify plasmids. These methods are often called “minipreps” because you are purifying DNA from a small volume of cells Plasmid purification is a technique used to isolate and purify plasmid DNA from genomic DNA, proteins, ribosomes, and the bacterial cell wall. A plasmid is a small, circular, double-stranded DNA that is used as a carrier of specific DNA molecules. Plasmids are circular, extra chromosomal, DNA molecules and in molecular biology they act as carriers, or vectors, for a specific DNA fragment. Bacteria are used to replicate plasmids, so that your DNA of interest is mass-produced. Plasmid DNA Purification Overview. Plasmid DNA purification is a cornerstone of many molecular biology and biochemistry labs due to its extensive use prior to a variety of applications such as, transfection, bacterial transformation, restriction endonuclease digestion, PCR, sequencing, and in vitro transcription.  A plasmid preparation is a method used to extract and purify plasmid DNA. Many methods have been developed to purify plasmid DNA from bacteria. These methods invariably involve three steps: 1  Growth of the bacterial culture.  Background Information. In order to use your Addgene plasmid, you will need to isolate plasmid DNA from the bacterial cells. To do this, you will lyse the host bacterial cells and separate the proteins, RNA and chromosomal DNA from the plasmid DNA. This procedure is generally referred to as a mini-prep.  If you want to isolate plasmid DNA, you crack your cells open and carry out a miniprep, trying very hard not to get any contaminating genomic DNA in your sample. If you want genomic DNA, you crack your cells open in a different way and try to isolate as much of the stuff as possible.  Theory. Plasmid is a double stranded, circular extra chromosomal DNA of bacterium. It is used in recombinant DNA experiments to clone genes from other organisms and make large quantities of their DNA. Plasmid can be transferred between same species or between different species. Proteins are contaminating agents in any type of DNA isolation so as in plasmid DNA isolation also. They can interfere with the final product and result with low yield. SDS is used to denature the proteins and facilitate the DNA purification process.
http://www2.muw.edu/~lbrandon/Genetics/plasmid.doc https://en.wikipedia.org/wiki/Plasmid http://public.callutheran.edu/~revie/protocols/Q-Minipreps.pdf http://www.jove.com/science-education/5062/plasmid-purification http://www.zymoresearch.com/dna/plasmid-dna-purification https://en.wikipedia.org/wiki/Plasmid_preparation https://www.addgene.org/recipient-instructions/purify-plasmid-dna/ http://bitesizebio.com/1660/plasmid-v-genomic-dna-extractionthe-difference/ http://vlab.amrita.edu/?sub=3&brch=77&sim=314&cnt=1
why isolate plasmid dna