Cell signalling

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Cell Signalling is the transfer of information, that controls the cell behaviour, whether from cell to cell, or from environment to cell.

There are many different types of cell signalling that vary immensely. About 10-15% of the genome codes for the creation of these cell signalling molecules. Most signals involved are chemicals but some can be physical signals such as light.

Different signalling mechanisms are used depending on how far the signal needs to travel. For short distances, there is a pathway between adjacent cells and takes place via a gap junction. The pathway sizes increase from gap junction, to contact dependant, where the signal is displayed on the surface and a receptor on another cell surface, for example, an immune response cell. Paracrine pathways secrete a signal into the interstitial fluid within the same tissue. The next longer pathway is Autocrine signalling and Synaptic signalling. The longest signalling pathway, which usually has the longest response time to the stimulus is Endocrine signalling, where the signal is secreted into the blood stream which flows around the body.

A signal molecule coming from either a long or short distance functions as a ligand by binding to a receptor. The ligand is the 'primary messenger', and its binding to the receptor often causes additional molecules inside the cell to receive the signal. These are known as 'second messengers' and they relay the signals to different parts of the cell, initiating a cascade of changes (to behaviour or gene expression) within the receiving cell[1].

There are 5 stages:

  1. Signal
  2. Reception
  3. Transduction
  4. Amplification
  5. Response

The effect of cholera on cell signalling

Cholera toxin binds to and enters only cells that have GM1 on their surface, including epithelial cells. Its entry into a cell leads to a prolonged increase in concentration of intracellular cAMP, which in turn causes a large efflux of Na+ and water into the large intestine. This therefore causes diarrhoea and dehydration.   

References

  1. Hardin, J. et al. (2011). Becker's World of the Cell. 8th ed. San Francisco: Pearson. p392-3.

Alberts, B., Johnson, A. and Lewis, J. (2008). Molecular biology of the cell. 5th ed. New York: Garland Science, Taylor & Francis Group, pp.629

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