Heat shock

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In biochemistry, heat shock is the effect of subjecting a cell to a higher temperature than that of the ideal body temperature of the organism from which the cell line was derived.

Heat shock proteins are a part of the cell's internal repair mechanism. They are also called stress-proteins. They respond to heat, cold and oxygen deprivation by activating several cascade pathways. Heat shock proteins are also present in cells under perfectly normal conditions. They act like ‘chaperones,’ making sure that the cell’s proteins are in the right shape and in the right place at the right time. For example, HSPs help new or distorted proteins fold into shape, which is essential for their function. They also shuttle proteins from one compartment to another inside the cell, and transport old proteins to ‘garbage disposals’ inside the cell. Heat shock proteins are also believed to play a role in the presentation of pieces of proteins (or peptides) on the cell surface to help the immune system recognize diseased cells.

In fish that survive at 0°C, heat shock can be induced with temperatures as high as 5°C, whereas thermophilic bacteria that proliferate at 50°C will not express heat shock proteins until temperatures reach approximately 60°C [1]. The process of heat shocking can be done in a CO₂ incubator, O₂ incubator, or a hot water bath.

Induction of heat shock is a method by which genes can be introduced into cells via a vector. This is done by mixing the vector with competent bacteria in a microcentrifuge tube. First, the tube is cooled to a low temperature for several minutes, usually with an ice bath. The tube is then quickly moved into warm water, preferably around 40°C. This sudden change in temperature causes the pores to open up to larger sizes, allowing DNA molecules to enter. After a brief interval, the tube is quickly cooled to a low temperature again. This closes up the pores, and traps the DNA inside. With this, the cells would have been transformed. However, it must be noted that, as with almost all transformation techniques, this method is far from 100% efficient.