Introduction The bacteria used in this experiment is Escherichia coli which is not naturally competent. E. coli is a gram negative rod shaped bacteria and a facultative anaerobe. This bacteria forms part of the bacterial flora in the human intestine tract. The competence of a bacteria is based on its ability to take up naked DNA from the environment and incorporated on theirs, transformation. Alteration in the permeability of the membranes allows DNA to cross the cell envelope of E. coli. Since the outer membrane of the E. coli is mostly negatively charged and the DNA molecule also has a negative charge, then the addition of CaCl2 will neutralize the interaction so that the naked DNA molecule can enter the cell. (Microbe Library web) Another important factor on the competence of the bacteria is a procedure of alternating temperature between ice bucket and heat shocks. By the combination of this two procedures E. coli becomes competent. This procedure was first reported by Mandel and Higa. (Singh 562) Even though it works it is only believed that CaCl2 helps DNA absorption to cell surface and the heat-shock step facilitates penetration of absorbed DNA into cell. (Panja 411) The main purpose of this experiment is to transform the bacteria to make it resistant to the antibiotic ampicillin. A secondary transformation is being made, and
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