What are the 5 well-known enzyme-linked cell surface receptors? - Answer- 1. Receptor Guanylyl Cyclase: produces cGMP
2. RTK: phosphorylate tyrosine residues leading to association of signalling molecules and cascade
3. TK Associated Receptors: associate with proteins having TK activity
4. Rece...
what are the 5 well known enzyme linked cell surfa
how are rtk and tk associated receptors different
what is the reciprocal of rtk
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CPPS 325 FINAL EXAM
What are the 5 well-known enzyme-linked cell surface receptors? - Answer- 1. Receptor
Guanylyl Cyclase: produces cGMP
2. RTK: phosphorylate tyrosine residues leading to association of signalling molecules
and cascade
3. TK Associated Receptors: associate with proteins having TK activity
4. Receptor Tyrosine Phosphates: Removes phosphate on tyrosine residues
5. Receptor Serine/Threonine Kinases: phosphorylate specific Serine/Threonine
residues on IC signalling molecules
How are RTK and TK Associated Receptors different? - Answer- RTK phosphorylate
tyrosine while associated receptors bind/find proteins with TK activity to initiate the
cascade of signalling.
What is the reciprocal of RTK? - Answer- Receptor Tyrosine Phosphatases. They take
the phosphate off the tyrosine residues to inactivate signalling cascades.
Ex. Transforming GF Beta superfamily of receptors, cell type dependent.
What is the major mechanism for receptor signal transduction? - Answer- Tyrosine
kinase phosphorylation
RTK vs. Serine/Threonine Phosphorylation ? - Answer- Tyrosine phosphorylation is rare
(1%) relative to serine/threonine residue phosphorylation. Tyrosine phosphorylation is
the major mechanism of receptor signal transduction.
What is the net effect of activated TKs? - Answer- Tyrosine phosphorylation on target
proteins.
What are amplifiers of the TK pathways? - Answer- PI3-K -> PIP3
PLC -> DAG and InsP3&Ca2+
What are RTK mediated actions in the cell? - Answer- regulation of cell proliferation,
differentiation, and cell motility, promotion of cell survival and modulation of cellular
metabolism.
TKs exist in either the cytosol or as transmembrane receptors, what are the differences
in the two types? - Answer- Cytosol receptors have an src N-terminal region. Cytosol
has no membrane spanning domain.
TM receptor has a single membrane spanning hydrophobic TM domain. Ex) Epidermal
GF RTK.
,What is src? - Answer- Src is a non-receptor TK, so it does not span a membrane. It is a
tyrosine kinase. And although it is cytoplasmic TK it can still bind to activated RTKs.
What is contact inhibition confluency? - Answer- Stops Src domains signalling and
therefore cells stop dividing.
If there is an issue then cancer can result and mutation causes an inhibition of the stop
signal so the cells keep growing and dividing.
What are SH domains? - Answer- Src homology domains. Src and other proteins that
have src-homology domains can bing to activated RTKs.
What are the different SH domains in proteins? - Answer- There are SH1, SH2 and SH3
domains.
What isSH1 domain characterized by? - Answer- Catalytic domain of a protein, for
example the receptor. and it has the kinase activity. It is responsible for phosphorylating
tyrosine residues.
What is SH2 domain characterized by? - Answer- Binds peptides with consensus
(positional information on C-terminal side of the phosphorylated tyrosine).
Very specific.
Mediates protein-protein interactions in cellular signalling cascades. Very common in
proteins outside the src family.
What do SH2 and SH3 domains have as a common funciton? - Answer- They mediate
protein-protein interactions in cellular signalling cascades.
Very common in proteins outside the src family.
What is SH3 domain characterized by? - Answer- Interacts with proline-rich peptide
targets (minimal consensus). Mediate protien-protein interatctions in the cellular
signalling cascade. Very common in proteins outside the src family.
What are PTB domains? - Answer- (Phosphotyrosine binding domain)
Bind to phosphorylated tyrosine. Functional equivalent of the SH2 domain, except for
the positional informational. Is not the C-terminus like SH2, but the N-terminus side of
the phosphorylated tyrosine.
shc is a PTB protein.
What is the normal action that stops signalling for cell division in the src pathway? -
Answer- Contact Inhibition Confluency
How do PTB and SH2 domains differ? - Answer- SH2 domains binds consensus on the
C-terminus.
PTB domains binds the N-terminus.
They both mediate cellular signalling.
, What is shc? - Answer- PTB protein that docks at the N-terminus consensus docking
site.
What activates a RTK? - Answer- Ligand/agonist binding
Upon ligand binding the two activation pathways are? - Answer- 1. Conformational
change
2. Dimerization
What happens with conformational change activation? - Answer- A conformational
change that is sufficient enough to activate SH1/catalytic domain results in
phosphorylation.
What is the only example of conformational change activation? - Answer- Insulin
receptor kinase.
All other RTKs are activated through forms of dimerization.
What are the two forms of dimerization? - Answer- i) Receptors exist as unactivated
dimers until ligand binds (Twist theory)
ii) exist as monomers that are brought together and activated by ligand binding.
What is the most common method of dimerization activation? - Answer- Receptors
existing as monomers.
What is the Twist Theory? - Answer- RTKs exist as formed dimers and when a ligand
binds the dimer undergoes a twist/shift in shape so the catalytic domains can become
fully active and therefore allow for autophosphorylation in key tyrosine residues outside
the catalytic domain.
What is the monomer dimerization activation pathway? - Answer- The monomers need
to dimerize to fully activate the TK/SH1 domains.
Ligand must bind external domains of two monomer RTKs so they dimerize. This results
in increased enzymatic activity of the IC catalytic SH1/TK domains by phosphorylating
key tyrosine residues outside the catalytic domain. Transphosphorylation of tyrosines
occurs so the kinase activation can occur, and transphosphorylation of regions that
create the docking site. The phosphorylated tyrosine residues serve as docking sites for
cytoplasmic signalling molecules.
What does RTK activation require? - Answer- Dimerization and transphosphorylation!!
Where are tyrosines phosphorylated - Answer- They are first phosphorylated within the
kinase/catalytic domains to increase the activity of enzyme and this triggers
phosphorylation outside the catalytic/kinase domain that produces a docking site.
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