Artificial Transformation and the role of calcium chloride-heat shock treatment

Question: What are the roles of CaCl2  and heat shock in artificial transformation ? 

Answer: 

Artificial transformation is accomplished by inducing competence in cells by using chemicals or electroporation. The most common method of making competent cells is CalCl2 and heat shock treatment. In this technique an early log phase culture is centrifuges and re-suspended in a cold, hypo-tonic CalCl2 solution, and after that DNA is added to these cells, followed by a brief heat shock, which allows transportation of the DNA into the cell. The roles that CalCl2 and heat shock play in accomplishing this, are as follows-

1.  The cell membrane itself made up of lipid molecules that have negatively charged phosphates.  These phosphates repel the negatively charged DNA helix and prevent its adsorption and entry  into the cell.
   
   
   
   
2. Calcium ions from CalCl2 forms a calcium DNA complex and those ions also interact with the negative charges creating an electrostatic neutral situation.
   
   
   
   
3. This allows adsorption of the calcium DNA complex to the cell surface.
   
   
   
4. Lowering the temperature congeals the lipid membrane stabilizing the negatively charged phosphates and making them easier to shield.
   
   
5. Now a rapid rise in the temperature, or heat shock creates a temperature imbalance on either side of the bacterial membrane ( High temperature outside and low temperature inside) and sets up a current. with the ionic shield in place, the DNA can then enter through the cell membrane.
   

   
   
   

Further reading: 

1. Microbial Genetics, David Freifelder 
2. Animation of artificial transformation