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BIOB11H3 Lecture Notes - Barber Surgeon, Signal Transduction, Paracrine Signalling

Biological Sciences
Course Code
Dan Riggs

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Lecture 21 - Signal transduction I
We will talk about the general signaling pathway and about some early experiments that
started the signaling research going. This starts in chapter 15. Cellular communication and
signal transduction are what we are going to talk about for the next couple of lectors. There
are three basic strategies that multicellular organisms use to respond to extracellular
signaling molecules. The first one is self and in figure 15 1, you see in the first panel
something called an autocrine signal. Auto means self so what happens is that the cell in
the middle is making some type of signaling molecule that is secreting from the cell and it's
in the local environment but the cell itself that made the signal is now receiving the signal
at a receptor at its cell surface. This is important for a variety of cell regulations. The
second mechanism is known as local signaling and the technical name is paracrine
signaling. In this case there is the cell in the middle that is making signaling molecules in
yellow and in this case it affects its neighbors in the nearby vicinity through diffusion are
receiving the signal and setting in motion a set of events to respond to the signal. Lastly,
there is a way for multicellular organisms as a systemic way to signal. Endocrine glands
make signals like hormones and they send those hormones into the circulatory system
where they can be unloaded at very distant sites to control cells that are in fact very far

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Figure 15 2 looks complicated but is not. Basically know the notes that are on the right
side of the slide. At the top is a signaling cell which has made a signal for example a
hormone. The cell membrane is shown in blue and you see some transmembrane receptors
that are present. The response of the second cell can only take place if that cell can see the
signal. That is, if it has a receptor that binds to that particular signal then something is
going to happen. If it cannot detect the signal that is if it doesn't have the receptor, then it
obviously will not direct the response. This is important. There are two types of response
pathways one on the left and one on the right. Simplistically they could be said to be with
or without that effector molecule. This takes place inside the plasma membrane where the
receptor becomes activated. Usually, there are several steps which can be branch
pathways, pathways inactivating other pathways, and depending on the response pathway,
the results can vary dramatically. For example, for a specific type of stimulus, it might cause
some of the muscle cells to contract where as it would cause other muscle cells like your
heart or lungs to relax so that you can get more oxygen so the heart to beat faster etc to
allow you to respond to some stimulus. As you see at the bottom of figure 15 2 the
outcomes are quite variable. It can be a simple metabolic change, it can be cell death, the
cell might move or cause translation, which may improve its survival, transcription may be
altered the cytoskeleton may be altered, or some combination of these things to eventually
arrive at a response.
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