Definition of a cellular signal

Richard Norman rsnorman at
Tue Sep 19 09:28:13 EST 2000

"Jan Behrends" <j.behrends at> wrote in message
news:8q7pt3$l7a$1 at
> I think what Vladimir is really asking for is some information-theoretical
> definition of a cellular signal. It is true that we're always speaking of
> e.g. "synapses transmit information from cell a to cell b" without having
> any too specific idea about where the information actually is. The same
> might be true for many kinds of cellular signals. Classical information
> theory was made for telegraph lines, where the rules of encoding are
> but we don't really know them for communication between cells. This might
> one reason for the difficulty. I'd be also  interested in a general
> definition of the concept.
> Jan

If that is the case, then I think you are in for some difficulty.  Biology
does not
work like physics, where everything has a neat, clean equation.  Many
signals can bind to one receptor to produce an effect.  One signal can bind
many different receptors to produce different effects.  The effect is
on the cell state -- what other signals the cell is receiving or has
received recently
(or in the distant past) as well as metabolic conditions, etc.  Not to
mention that
even the basic rules for what a cell does varies tremendously from species
species,  from cell to cell within one species, and from time to time within
one cell.

Basically, cell A can influence cell B by touching it or by releasing a
which touches it.  The "touch" can be binding to a receptor on the outside
cell B but it can also be a steroid hormone or thyroxine that passes through
membrane and binds to a receptor inside cell B.  Then, as a result of the
receptor binding, things happen.   Very often a second messenger is involved
and possibly a tertiary ...  Synaptic transmission is one very specialized
of cell signaling.  The details fill the cell biology literature.

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