PSIO 404 Exam 3 Flashcards
Very briefly discuss the importance of heptahelical receptors.
heptahelical receptors are 95% GPCR but no all of them.
There are some were the N terminus faces the inside of the cell (this is abnormal)
-most abundant receptor type, encoded by one of the largest gene families
-best known are GPCRs which act as GEF (GDP-GTP exchange factor) involved in practically every aspect of cell life
Briefly discuss the general structures of heptahelical receptors.
GPCR-
seven transmembrane domains that offers nearly unlimited variability to adjust to any possible shape of signal molecules where bulky ligands bind to extracellular loops
Discuss the principle of multiple receptors as it applies to GPCRs.
a particular GPCR in the membrane gives you a coupling to a particular G protein and also the same particular protein in the membrane and through a series of modifications varying which kind of G protein it can couple with
Discuss the principle of variable G-protein coupling.
by their effectors, second messengers are able to control variable G-protein coupling
like built on negative feedback
Describe the activation of rhodopsin by light.
rhodopsin binds 11-cis-retinal unit it is converted by light into 11-trans-retinal which breaks a salt bridge between transmembrane helices 3 and 7 as it is formed, this separation of helices 3 and 7 permits the binding of Galpha subunit of transducin (the G protein coupled to rhodopsin) which then stimulated PDE6 degrades cGMP and cause hyperpolarization of the rod or cone which all the transmission of light into the brain
Describe some structural/functional characteristics of rod cells.
within the outer segment of the rod cell disc there are rhodopsin proteins
rod cells only tell you if there is light or not and and cones tell you the shades of color
rod cells are high sensitive can detect 1 photon or a million photons
Explain four benefits of GPCR oligomerization.
- noise filtering
- alteration of ligand specificity
- alternation ligand sensitivity
- alternation of receptor function
Discuss β-adrenergic signaling in skeletal muscle.
when noradrenaline binds to B2 receptor, which stimulates g protein coupling (Gs), which activates adenylate cyclase which activates cAMP production which activates PKA. PKA inhibits glycogen synthase but it also promotes the activity of glycogen and phosphorylase kinase. phosphorylase kinase promotes glycogenolysis which promotes glycogen release. But in order for phosphorylase kinase to be activated it also needs calmodulin which gets activated through calcium
Discuss the effect of voluntary muscle contraction on glucose release in skeletal muscles.
when acetylcholine binds to a nicotinic receptor this leads to calcium entry or calcium to increase within the cell which is needed for voluntary muscle contraction. This calcium can be used to activate calmodulin which can now activate phosphorylase kinase leading to the release og glucose
Discuss β-adrenergic signaling in adipocytes.
when noradrenaline binds to beta 3 and it activates the alpha subunit of the stimulatory g protein this activates adenylate cyclase which activates cAMP production which will activate PKA. PKA will inhibit perilipin and protimote lipase. lipase promotes lipolysis which promotes fatty acid release into the bloodstream.
Discuss α-adrenergic signaling in vascular smooth muscle.
when noradrenaline bind to alpha 1 receptor and activates of g protein of the q11 subfamily. This activates phospholipase C which leads to the break down of PIP2 into InsP3 and DAG. InsP3 diffused into the cytoplasm when it binds to smooth ER and cause calcium release and DAG is set free into membrane where it activates protein kinase C. From the calcium released this activates myosin light chain kinase which activates actomyosin complex which lead to contraction and blood pressure to rise
Discuss negative-feedback α-adrenergic signaling in sympathetic neurons.
when noradrenaline binds to alpha 2 receptor and activates the g i,o proteins, this causes 2 things to happen. the inhibition of ca channel and adrenylate cyclase and the promotion of k channel. The opening the potassium channel cause hyperpolarization to the neuron. the inhibition of the ca channel and adenylate cyclase prevents cAMP production which normally activated ca channels which decreased contraction for blood pressure falls
Describe the evoking of sympathetic effects via ACh muscarinic receptors and their associated G-protein families.
Gq,11 = M1,M3,M5 which promote smooth muscle contraction (lung, intestine, pupil) non viscous saliva and secretion of gastric acid and digestive enzymes
Gi,o = M2,M4 which promote through inhibition smooth muscle relaxation and decrease heart rate
Explain the integration of β-adrenergic and ACh muscarinic receptors in cardiac pacemaker cells.
since we know when noradrenaline bind to beta 2 receptor (through the sympathetic) this activates g stimulatory protein activating the production of cAMP which promotes the opening of HCN channel leading to increase in HR. When acetylcholine binds to the m2 receptor (through parasympathetic) this activates g inhibitory family which stimulates the opening of k channels and inhibits the production of cAMP leading to the closure of HCN channels and lowering HR. The cell will do whatever signal is greater, if the signals are the same the cell will not change activiy
Discuss PAR function as an example of a protease switch: how it is both expensive and highly effective in terms of signaling.
since protease activated receptor (PAR) activation is irreversible it is expensive but extremely effective
What does “G-protein promiscuity” mean?
g protein promiscuity means that it can bind to multiple g protein coupled receptors, Gq, Gi,o, and G12,13 proteins
Discuss 3 principles of GPCR adaptation to overstimulation.
- desensitization - within seconds of becoming activated, receptors become desensitized
- internalization and sequestration - desensitized receptors are internalized and sequester
- recycling or downregulation - sequestered receptors are either recycled back to the membrane or destroyed by proteolysis in lysosomes
Describe the typical life cycle of a transmembrane receptor
through the rough ER and golgi transmembrane receptors can be created and then through exocytotic vesicles lead them out of the cells and through exocytosis out of the cell, then old transmembrane receptors through endocytosis are brought back into the cell and brought to endosomes where they can be destroyed through lysosomes or recycled back to the golgi and rough ER
Describe in depth desensitization of GPCRs.
a strong input signal leads to desensitization of GPCR within seconds
- GPCRS are phosphorylated by a GPCR kinase (GRK) or a downstream kinase (like PKA) and uncouples the receptors from the g -proteins
-a desensited GPCR will be bound by an arrestin protein (an arrenstin takes the place of the g protein) making it an arrestin coupled signal
-an arrestin also induces internalization of the receptor
*arrestin coupled signaling can occur anytime arrestin is bound especially before internalization
Describe in depth internalization and sequestration of GPCRs.
now that GPCR are bound to arrestin, this allows for clathrin to also bind and this causes a pit to form in the membrane. When this clathrin coated pit, there are desensitized receptors. Arf6, ARNO, AP2, clathrin, and arrestin are all bound to this GPCR this all for dynmin to begin to for a ring and bing to pinch off the vesicle and become an endosome. This endocytotic vesicle can be delivered to the lysosomes and become destroyed or can be sequestered and returned to the plasma membrane
Describe in depth recycling or downregulation of GPCRs.
so if the receptors become sequestered then two things can happen
1. they can be destroyed by lysosomes through downregulation (down-modulation)
2. they can be recycled through the golgi apparatus back to the plasma membrane no longer desensitized
-a cell has to go through a recovery phase to become resensitized
-this is made possible by dephosphorylation of GPCR by a GPCR specific phosphatase (PP2A)
-then an exocytotic recycling vesicle will bring the GPCR back to the membrane
-this can only be done with a short term overstimulation long term gets destroyed
Describe β-adrenergic signaling as an example of GPCR adaptation, and identify the level of adaptation which involves MAO & COMT DO not do this one
this can happen at two levels
1. extinction of the input signal by dilution (synaptic re uptake) or by metabolic inactivation thanks to enzymes like COMT or MAO
-COMT and MAO modify norepinephrine to make it less able to activate the receptor
Discuss the amplification of a signal (the extreme sensitivity) which occurs in a rod cell when it detects a photon, and explain the need for adaptation by rod cells
Briefly discuss the two criteria which determine maximal receptor performance.
- adaption - which allows us to be as sensitive as possible
- rapid temporal discrimination - which all the rod cells to process the arrival of a photon to change their activity and then rest and be ready for the nest photon within 150 microseconds