Thursday, January 15, 2009
Molecular language: how cells communicate
This is an article that appeared in the 5th edition of El·lipse, the PRBB monthly newspaper.
Communicate or die, that’s the law for cells. Cells need to be aware of what’s happening in their environment and react accordingly. For that, they have very complex signalling mechanisms, which, unless the signal is diffusible, tend to start with a receptor protein located at the membrane of the cell (what separates the cell from its surroundings). This receptor senses a signal from the environment and then triggers a cascade of proteins that will activate other proteins, and so on; this is called a signalling cascade. In eukaryotic cells such as the human ones kinases and phosphatases - a type of proteins that add or remove a chemical group to other proteins and modify their activity - are frequent components of these signalling pathways, The signalling cascade will finish in the nucleus, the part of the cell where the DNA is stored, and will either activate or repress certain genes. The action of these genes will dictate the response to the initial signal.
The signals that trigger a reaction in a cell can be external, such as several types of stress, including starvation, heat shock or osmotic stress. However, the stress signal can be endogenous, as observed for oxidative stress: the use of oxygen during respiration can generate reactive species as a side-product, and these species can damage all types of biomolecules, including DNA.
Furthermore, cells also need to talk to each other in order to behave as a whole within the organism. These cell-to-cell signals can be through physical contact or through molecules that are released from one cell and captured by another.