chapter 14 sensory and signal transduction Flashcards
what does epinephrine bind to
b-adrenergic receptor
which molecule is changed when a photon binds rhodopsin
11-cis-retinal til 11-trans retinal
what could be an inhibitor of epinephrin’s binding to B-adrenergic receptor
carazolol
G-protein consists of
3- domains
alpha binds the nucleotide (p-loop NTPase)
beta
gamma
What happens when GTP is bound to G protein
the B and Y subunits dissociate. so alpha can transmit the signal to other targets
one hormone-complex can stimulate the nucleotide exchange in many
G-proteins
what does cAMP activate and how does it do it
protein kinase A
by binding to the regulatory chains releasing the catalytic domains which are active on their own
what does PKA or protein kinase A consist of
2 regulatory chains
2 catalytic domains
what does PKA stimulate besides the activation of downstream targets
it activates the expression of specific genes by phosphorylating a transcriptional activator called the cAMP response element binding protein (CREB)
how is the adrenergic receptor deactivated
GRK2 phophorylates the carboxyl-terminal of the hormone-receptor complex
B-arrestin binds to the phosphorylated hormone receptor complex and diminishes the ability to activate G proteins
PIP2
phosphatidylinositol 4,5 bisphosphate cleaved by phosphlipase triggered by the angiotensin iI receptor, yielding diacylglycerol DAG + inositol 1,4,5-trisphosphate
what does DAG do
remains in the plasmamembrane. activates protein kinase C phosphorylating many serine and threonine residues in many protein targets. Also requires that the protein kinase C is bound to ca2+
what makes ca2+ able to inducee structural changes in proteins
because it has a capacity to be coordinated to several ligands (6-8) oxygen atoms. allowing it to cross-link different segments of a protein
calmodulin
regulatory protein four ca2+ bindingssites
EF-hands (helix loop helix)
calmodulin regulates calomodulin dependent protein kinases, that phosphorylate many targets regulating fuel metabolism, neurotransmiter synthesis, release and so on.
ca2+ coordinated by 7 oxygen atoms
in insulin receptor the tyrosine kinase is
a part of the receptor
the activation in insulin receptor
lies in the center of the structure
when the tyrosin residues are phosphorylated the activation loop crosses around making the structure more compact
how does insulin bind and activate insulin receptors
approachs the space between the alpha subunits and the alpha subunits get closer to each other, which then causes the beta-subunits to approach each other and then the activation domains from each beta-subunit fits in the active site of the tyrosine kinase in the other beta-subunit causing the phosphorylation of tyrosin and giving the receptor its active conformation
adaptor proteins are not
enzymes
How is insulin signaling terminated
by the action of phosphatases
1- protein tyrosine phosphatase ( removing phosphoryl groups from insulin receptor and IRS)
2- Lipid phosphatase (PIP3 to PIP2)
3- protein serin phosphatase to deactivate Akt1
what structural feature causes the dimerisation of EGF-receptors
what happens when EGF is absent
dimerisation arm from each subunit
the dimerisation arm is bound to its receptor preventing it from binding to the other receptor
cross phsosphorylations in EGF-receptors
carboxyl-terminals rather than activation loops
when is the kinase in egf-receptor activated
activated without phosphorylation
GAPs
GTPase activating proteins (GAPs)
In insulin and EGF-receptor mediated pathways
both act as tyrosin kinases
