3 Flashcards
b-carotene is oxidized to —-?
Retinal
Light acts on 11-cis retinal and converts it to ?
an all-trans isomer
what is the g-alpha protein in vision?
Transducin
How do visual signals stop?
Opsin dissociates from all-trans retinal to stop visual signal
what keeps voltage gated cation channels open?
cGMP
What happens when a photon appears? (steps of pathway)
-all trans-retinal causes opsin to activate Ga protein (Transducin)
-Gat (Transducin) activates Phosphodiesterase (PDE6)
-PDE cleaves cGMP into GMP
-Na+ (Ca2+) channel closes 1st due to low cGMP levels
-membrane potential becomes hyperpolarized, closes Ca2+ channels
-glutamate efflux drops so less signaling to visual cortex
-brain perceives LIGHT
Recovery process? (STEPS)
- low Ca2+ levels cause Recoverin and Rhodopsin Kinase to dissociate
- Rhokinase is free to phosphorylate isomerized rhodopsin freeing it from transducin
- Arrestin binds to this phospho-rhodopsin to shut down the process
- the dark current is resetting
what is the GPCR in the vision pathway?
Rhodopsin = opsin (bound to 11-cis retinal)
what cleaves cGMP to GMP
PDE6
(phosphodiesterase)
Shutting things off recovers system!
steps
-dark adaptation (recovery) requires low Ca2+ levels to activate GC activating protein
-RGS proteins speed up cleavage of GTP (active) to GMP (inactive) by Transducin
What proteins act in the reverse of PDEs?
Adenylate cyclase (AC): Converts ATP to cAMP, counteracting PDEs that degrade cAMP.
Guanylate cyclase (GC): Converts GTP to cGMP, counteracting PDEs that degrade cGMP.
What is another name of an ionotropic receptor?
ligand-gated ion channel
Sev is a —- and is linked to —- signalling
Sev is an RTK and is linked to Ras signaling
RTKs characteristics/activation
- has extracellular and intercellular domain
- Binding of ligand induces dimerization of RTK monomers. Cross phosphorylation occurs in intercellular domain to activate downstream cascade
- receives signalling like hormones, GFs, etc..
what proteins are in Ras superfamily?
Ras family – Regulates cell growth, differentiation, and survival.
Examples: Ras (KRas), Rheb
Rho family and members ?
Rho family – Controls the cytoskeleton, cell shape, and motility.
Examples: RhoA, Rac1, Cdc42
