Heat shock
In biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

, heat shock is the effect of subjecting a cell to a higher temperature than that of the ideal body temperature
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...

 of the organism from which the cell line
Cell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...

 was derived.

Heat shock response

The cellular response to heat shock includes the transcriptional up-regulation of genes encoding heat shock protein
Heat shock protein
Heat shock proteins are a class of functionally related proteins involved in the folding and unfolding of other proteins. Their expression is increased when cells are exposed to elevated temperatures or other stress. This increase in expression is transcriptionally regulated...

s (HSPs) as part of the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

's internal repair mechanism. They are also called stress-proteins. and respond to heat, cold and oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 deprivation by activating several cascade pathways
Biochemical cascade
A biochemical cascade is a series of chemical reactions in which the products of one reaction are consumed in the next reaction. There are several important biochemical cascade reactions in biochemistry, including the enzymatic cascades, such as the coagulation cascade and the complement system,...

. HSPs are also present in cells under perfectly normal conditions. Some HSPs, called chaperones, ensure 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 misfolded proteins to fold into their correct three-dimensional conformations, which is essential for their function. They also shuttle proteins from one compartment to another inside the cell, and target old or terminally misfolded proteins to proteases
A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....

 for degradation. Heat shock proteins are also believed to play a role in the presentation of pieces of proteins (or peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...

s) on the cell surface to help the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

 recognize diseased cells.

The up-regulation of HSPs during heat shock is generally controlled by a single transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...

; in eukaryotes this regulation is performed by heat shock factor
Heat Shock Factor
Heat shock factor , in molecular biology, is the name given to transcription factors that regulate the expression of the heat shock proteins. A typical example is the heat shock factor of Drosophila melanogaster.- Function :...

 (HSF), while σ32 is the heat shock sigma factor
Sigma factor
A sigma factor is a bacterial transcription initiation factor that enables specific binding of RNA polymerase to gene promoters. Different sigma factors are activated in response to different environmental conditions...

 in Escherichia coli.

Inducing heat shock

In fish that survive at 0°C, heat shock can be induced with temperatures as low as 5°C, whereas thermophilic bacteria
A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 122  °C . Many thermophiles are archaea...

that proliferate at 50°C will not express heat shock proteins until temperatures reach approximately 60°C. The process of heat shocking can be done in a CO2 incubator, O2 incubator, or a hot water bath.
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