Explanatory chapter: how plasmid preparation kits work
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Updated: May 8, 2026

09:24
Purifying Plasmid DNA from Bacterial Colonies Using the Qiagen Miniprep Kit
Published on: July 29, 2007
1Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Methods in Enzymology
|September 10, 2013
Abstract:
To isolate plasmid DNA from bacteria using a commercial plasmid miniprep kit (if interested, compare this protocol with Isolation of plasmid DNA from bacteria).
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Plasmids
Plasmids are extrachromosomal DNA molecules found in bacteria, archaea, and some eukaryotic microbes like yeast. These small, circular DNA structures typically contain fewer than 30 genes, although some may exist linearly. Plasmids vary in their number within a cell, known as copy number. Single-copy plasmids are present in one copy per cell and multi-copy plasmids are present in multiple copies, reaching over 100 copies per cell.Plasmids usually replicate independently of the chromosomal DNA...
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DNA isolation protocols can be fast and straightforward or complex and time-consuming depending on the type and quality of DNA required for further processing. For example, plasmid DNA extraction is a bit more complicated than genomic DNA extraction because of the need for an appropriate lysis method to separate plasmid DNA from gDNA during isolation. However, for specific applications, such as long-range DNA sequencing that require a good yield of high- quality DNA samples, we need to follow...

