We have a signal!

 

Signal Transduction is the process by which a surface recognition of a message is converted into a cellular response (Below)

  1. Signal detection
  2. Chemical Process
  3. Cell Response

An example of signalling from the point of reception to cell response can be seen HERE!

The overall processes that are incorporated with this ‘signalling cascade’ eventually results in alterations to the cell, for example gene transcription or switching on important enzymes needed by the cell, put simply; there is a major reason why these signalling processes are carried out. Firstly, what are these cell receptors? There are several types of receptors, but to keep it short I have mentioned a couple,

  1.  G-Protein coupled receptors
  2.  Tyrosine Kinases

They are essentially integral membrane proteins that span a transmembrane region on a cell (shown below).

 Source

The series of loops (purple) that can be seen tells us the structure of this particular integral membrane protein, better known as alpha-helices, and the class in which it falls under, in this case G-Protein Coupled Receptors

 There are many classes of these receptors each with their own way of interpreting outside signals to chemical processes within the cell. The cellular machinery which converts this signal involves many proteins (usually kinases) that phosphorylate and ‘switch on’ certain enzymes. A Protein Kinase is a type of enzyme that will transfer a phosphate group to a specific substrate, this process known as phosphrylation. Kinases are important in cell signalling since they activate downstream proteins needed to carry the signal all the way to the end.

How are these important in human health? I’m glad you asked! Researchers, namely Biochemists, study these receptors and their associated cellular processes to find out how certain molecules bind to these receptors which could have medical significance in relation to toxins (Scroll down in this link to see Diphtheria toxin for a good explanation), which can invade these cell surface receptors and cause many problems throughout the body.

The job of the Biochemist is to figure out the structure of these toxins and hopefully produce a vaccine that will ultimately bind to these toxins to cause an immune response thus destroying these toxins before they reach cell receptors prior to a second encounter of the same toxin.

So what activates Cell receptors?

  1. Amino acids
  2. Hormones
  3. Peptides
  4. Individual ions

Answer: All of the above

A very simplified diagram can be seen below that illustrates a Tyrosine Kinase receptor with several of its Tyrosine residues seen in the cytosol.

Source: CyberMedicine

In the example, signal molecules attach to the extracellular domain of the receptor (The outside part), dimerizing the receptor and activating phosphorylation of several Tyrosine residues along the Intracellular (cytosol) domain of the receptor. Other Proteins will come along, and this is where the downstream effects begin, and become phosphorylated (Activated Proteins), which then create a cascade of events causing a cellular response.