Question

DNA being hydrophilic cannot pass through the cell membranes of a host cell. Explain how does recombinant DNA get introduced into the host cell to transform the latter.

Answer 1

DNA is hydrophilic and cannot directly pass through the hydrophobic cell membrane of a host. To introduce recombinant DNA into a host cell, the bacterial cells are first made “competent” to take up DNA. This is achieved by treating the cells with a specific concentration of a divalent cation, such as calcium, which increases the permeability of the bacterial cell membrane by creating pores. The competent cells are then incubated with recombinant DNA on ice, followed by a brief heat shock at around 42°C, and then placed back on ice. This heat shock creates thermal imbalance across the membrane, facilitating the uptake of recombinant DNA into the cell. This process by which foreign DNA is introduced into a host to transform it is called transformation. In addition to this chemical method, other methods such as microinjection and biolistics (gene gun) are used in animal and plant cells respectively to deliver recombinant DNA directly into the cell or nucleus.