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A cold shock is when bacteria undergo a reduction in temperature, likely from their environment dropping in temperature. To constitute as a cold shock the temperature reduction needs to be both significant, for example dropping from 37°C to 20°C, and it needs to happen over a short period of time, traditionally in under 24 hours. Both prokaryotic and eukaryotic cells are capable of undergoing a cold shock response. The effects of a cold shock in bacteria include:


 * Decrease in cell membrane fluidity
 * Decrease in enzyme activity
 * Decreased efficiency of transcription and translation
 * Decreased efficiency of protein folding
 * Decreased ribosome function

The bacteria uses the cytoplasmic membrane, RNA/DNA, and ribosomes as cold sensors in the cell, placing them in charge of monitoring the cell’s temperature. Once these sensors send the signal that a cold shock is occurring, the bacteria will stop the majority of protein synthesis in order to redirect it’s focus to producing what are called cold shock proteins (Csp). The volume of the cold shock proteins produced will depend on the severity of the temperature decrease. The function of these cold shock proteins is to assist the cell in adapting to the sudden temperature change, allowing it to maintain as close to a normal level of function as possible.

One way cold shock proteins are thought to function is by acting as nucleic acid chaperones. These cold shock proteins will block the formation of secondary structures in the mRNA during the cold shock, leaving the bacteria will only single strand RNA. Single strand is the most efficient form of RNA for the facilitation of transcription and translation. This will help to counteract the decreased efficiency of transcription and translation brought about by the cold shock. Cold shock proteins also affect the formation of hairpin structures in the RNA, blocking them from being formed. The function of these hairpin structures is to slow down or decrease the transcription of RNA. So by removing them, this will also help to increase the efficiency of transcription and translation.

Once the initial shock of the temperature decrease has been dealt with, the production of cold shock proteins is slowly tapered off. Instead, other proteins are synthesized in their place as the cell continues to grow at this new lower temperature. However, the rate of growth seen by these bacterial cells at colder temperatures is often lower than the rates of growth they exhibit at warmer temperatures.