BIOB11H3 Lecture Notes - G Protein–Coupled Receptor, Guanine Nucleotide Exchange Factor, Protein Kinase

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Published on 21 Apr 2013
School
UTSC
Department
Biological Sciences
Course
BIOB11H3
Professor
Lecture 22 Signal transduction 2- G proteins/lipid derived signaling molecules/second
messengers.
G proteins are called that because they bind to guanine nucleotides, either to GTP or GDP.
We will also talk about lipid signalling and second messengers. There are a lot more
acronyms in this lecture so there's a lot of memorization needed.
Figure 15 2. What you see is the generalized signaling pathway. At the top is a signaling
cell or an external signal that the cell finds itself in the presence of. This extracellular
signaling molecule is often referred to as a first messenger or as the. Regardless of what it
is, either hormone or small molecule or ion, this takes place at the cell surface. There are a
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couple of different types of receptors that exist. Keep in mind that a cell can only perceive a
signal and it contains a receptor for that specific type of signal. The signaling ligand and the
signal has to match a receptor that exist usually at the cell surface as part of the plasma
membrane. Today we will talk about how the receptor gets activated and the series of
signaling events that take place in order to generate the response which can be a variety of
different things. What we will see today is that a single signal can generate a variety of
different responses in different tissues.
Most STP or signal transduction pathways, rely on changes in the phosphorylation states
of the molecules. Kinases are enzymes which phosphorylate target molecules. This action
is undone by phosphatases which take off phosphate from their target molecules. As seen
in the case of cyclin dependent kinase, some targets like CDK are active when they are
phosphorylated in a certain way and sometimes they are inactive when they are
phosphorylated. Others can only be active when they are dephosphorylated or phosphates
exist only in certain positions in the molecule. The utility of this provides a very quick
switch in order to take a protein that has already been made, so you don't have to go
through the trouble of activating gene expression or getting RNA polymerase to do the job,
making and processing the primary transcript, and exporting it to the cytoplasm,
associating with ribosomes to make a protein. No. You already have the protein made and
putting on or take it off a phosphate provides a quick switch to regulate protein activity.
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Figure 15 3 shows an example where a protein kinase cascade occurs. If we start at the
top, there is protein kinase 1 and by some unknown means, it became active in some way.
It looks around for its target molecule and it comes in contact with protein kinase 2. This
one is not active and can only be activated if protein kinase two on the left is in active and
can only be activated if the protein kinase one puts a phosphate group on to protein kinase
too. The same thing happens with in active protein kinase three which he needs one or
more phosphate groups from protein Kinase two to become active. One of the targets of
protein kinase three could be a transcription factor that is in active and studies have shown
that one transcription factors have been phosphorylated in a certain way, this changes
their structure such that a new clear localizations Signal is exposed and the transcription
factor can move from the cytoplasm to the nucleus for example and exert its effect. This is a
generic version of how these false correlations event might occur in a cascade to change in
gene expression. Question is what controls the phosphorylation of phosphatases earlier
than that.
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Document Summary

Lecture 22 signal transduction 2- g proteins/lipid derived signaling molecules/second messengers. G proteins are called that because they bind to guanine nucleotides, either to gtp or gdp. We will also talk about lipid signalling and second messengers. There are a lot more acronyms in this lecture so there"s a lot of memorization needed. What you see is the generalized signaling pathway. At the top is a signaling cell or an external signal that the cell finds itself in the presence of. This extracellular signaling molecule is often referred to as a first messenger or as the. Regardless of what it is, either hormone or small molecule or ion, this takes place at the cell surface. There are a couple of different types of receptors that exist. Keep in mind that a cell can only perceive a signal and it contains a receptor for that specific type of signal.

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