Calcium chloride (CaCl2) transformation is a laboratory technique in prokaryotic (bacterial) cell biology. It increases the ability of a prokaryotic cell to incorporate plasmid DNA allowing them to be genetically transformed. The addition of calcium chloride to a cell suspension promotes the binding of plasmid DNA to lipopolysaccharides (LPS). Positively charged calcium ions attract both the negatively charged DNA backbone and the negatively charged groups in the LPS inner core. The plasmid DNA can then pass into the cell upon heat shock, where chilled cells (+4 degrees Celsius) are heated to a higher temperature (+42 degrees Celsius) for a short time.