BIO 1140 Lecture Notes - Lecture 13: Threonine, Inositol Trisphosphate, Gluconeogenesis

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SIGNAL TRANSDUCTION PART 3
LECTURE 13
Tyrosene kinase receptors
At what point is the receptor active, able to transduce a receptor inside of the cell?
When the ligand binds to the receptor. As soon as the ligand binds to it, the monomorers each
bind a ligand and dimerize. The receptor has to autophosphorelate in order for the receptor to
become active
Ras has to become activated
GRB2 and SOS are needed to interact with SOS. Why? Why not just bind Ras to the receptor?
SOS and GRB2 are needed because Ras and the receptor are like puzzle pieces that don't fit. In
order to be able to interact with the phosphorelated tyrosenes, the protein needs a specific
domain/ shape. Ras does not have the proper shape to interact with any of the phosphorylated
tyrosenses. That shape is an SH2 domain. GRB2 is able to interact with the receptor but not Ras.
SOS is able to interact with GRB2, but not the receptor. So you stack them together in order to
relay the the information to the amplification enzyme.
The amplification comes because when Ras is activated, it will be able to transfer the
information to more than one target. As long as this cascade stays active, you can have more
than one Ras active, and each Ras can lead to the activation to more than one MAP Kinase.
Which in turn can lead to the activation of more than one trascripion factor (AP-1). This means
that the gene can be activated/ transcribed more than once. Many different RAN molecules will
be produced. All steaming from the same ligand binding to the receptor.
Ras is the amplifier: step that amplifies the message
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Phospholipase C: another amplifier enzyme. It does have an SH2 domain so it is able to interact
directly with the receptor without the need of an adapter protein.
When PLC is activated, it binds to the receptor, which activated the enzyme. It is a lipase so it
cuts lipids. It cuts PIP2 (Phosphatidyl inostiol bis-phosphate). When you cleave PIP2, you release
two things: InsP3 (inositol triphosphate) and DAG (diacylglyscerol).
We have already talked about IP3. What does it do?
It binds to an IP3 gated channel on the ER's membrane and allows the release of Calcium Ions.
IP3 goes on, activates another channel which releases calcium. you're going to have many more
Calcium ions than you're going to have ligand molecules (AMMPLIFICATION).
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Why does DAG (diacylglycerol) remain with the membrane after cleavage from PIP2?
DAG is involved in the activation of Protein Kinase C but it goes on and continues the
transduction of the signal. It is a second messenger.
Can it have a GPI anchor? What is a GPI anchor?
GPI anchor: Glycosil-based that are on the outer layer. Their job is to tag proteins for adhesion
recognition.
DAG is a fatty acid with a polar group cut off: almost a phospholipid.
How we are on the inner layer, we need something that is fatty acid anchored or prenol
anchored.
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