Role of calcium chloride during competent cell preparation?

Question

I am aware of the fact that $CaCl_2$ settles down on the cell wall making it less negative may be by forming bond with Teichoic acid. Also due to the positive charge it attracts DNA (DNA is negatively charged due to phosphate group). But is there anything else the $CaCl_2$ does? Also if its the work of $CaCl_2$ why we are adding $MgCl_2$ first in the standard protocol of the making competent cell preparation chemically?

Answer 1

This is a well studied topic and many scientists have asked your vary question! They found that any divalent ion will help attract the plasmid DNA to the cell; however, calcium has been found to have the added benefit of being readily absorbed by the membrane and once inside the cell, the calcium is easily neutralized. There is some debated as to how the pores by which the DNA enters the cells are affected by the calcium. Calcium weakens the membrane charge and increase permeability.

For a more comprehensive review, you may be interested in this paper: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5681917/