Final answer:
Preparations of uncut plasmid DNA typically contain both supercoiled and circular DNA forms. It's essential to follow the plasmid prep protocol carefully, as early steps profoundly affect DNA purity and yield. The prep aims to eliminate contaminants and produce sufficient DNA for further experimentation.
Step-by-step explanation:
Most preparations of uncut plasmid DNA from bacterial cells contain at least supercoiled and circular forms of plasmid DNA. It is crucial to follow the plasmid prep protocol precisely, as the steps from cell breakage to loading the DNA onto the purification column significantly affect the purity and quantity of the plasmid. When plasmids are prepared from bacterial cells, the DNA obtained is often contaminated with cell membranes, proteins, genomic DNA, and RNA. The prep process includes steps to remove these contaminants, utilizing the properties of plasmid DNA such as its high negative charge, water solubility, and relatively small size compared to genomic DNA.
One should note that plasmid DNA synthesized in bacteria is different from that generated via PCR amplification, mostly being supercoiled; supercoiled DNA is more compact and resistant to damage by endonucleases or environmental factors. During the plasmid prep, enough DNA needs to be synthesized to meet the requirements for subsequent experiments, which often demand DNA in the microgram to milligram range.