the heat shock transformation protocol is a basic technique in molecular biology which enables bacterial cells to take up circular plasma dna from the surrounding environment with this method we can bring genes of interest into bacteria and let them express those genes transformation is a process that also occurs in nature it is defined as the uptake of free genetic material from the environment bacteria contain the chromosomal dna and apart from that also autonomously replicating plasmid dna when another bacterium dies it might release some dna dna is a rather stable molecule and some bacterial strains are competent to take up exogenous plasmid dna genes from the foreign plasmid might be expressed and protein is produced the two main protocols for transforming bacteria artificially with plasmid dna are based on a short heat shock or on electroporation this video will demonstrate transformation using the heat shock protocol to make cells able to take up plasmid dna we must induce competence cells are chemically prepared to be competent by calcium chloride treatment the first step now is to keep these competent cells on ice for about 10 minutes after this we add the plasmid dna to our cells this plasmid contains the gene of interest we incubate the cell plasmid mixture for 30 minutes on ice the purpose of the calcium chloride is to bring the dna into close proximity with the lipopolysaccharides which are present in the bacterial outer membrane the divalent calcium cations cover both negatively charged dna and negatively charged lipopolysaccharides the third step involves the exposure to a short heat shock the tube is put from the ice directly in a water bath with 42 degrees celsius the heat shock should be between 30 seconds and a minute depending on the protocol or the bacterial strain the heat shock makes entering of the plasmid dna into the cytosol possible immediately after this the cell plasmid solution is put back on ice to recover growth medium is added to the cells and they are incubated with agitation at 37 degrees to regenerate the damaged cell membrane the incubation time is selected long enough so that the cell can even divide and express genes on the uptaken plasmid after that the cells will be plated on selective medium that means the medium contains antibiotics preventing growth of bacteria which are not resistant the plasmid used for transformation does not only contain our gene of interest but also a sequence coding for antibiotic resistance only bacterial cells successfully transformed with these plasmids can thus grow on the plates thanks for watching make sure to subscribe when you want to see more scientific videos also leave a like if this video was helpful for you bye