BIOL 2021 Lecture Notes - Lecture 13: Cyclic Guanosine Monophosphate, Guanylyl Cyclase, Phosphodiesterase
13 May 2018
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• Fig 15-6B GPCRs
o Extracellular signal = light.
• Fig 3-53A retinal
o Retinal isomerization.
• Retinal isomerization (wikipedia)
o Light causes changes from 11-cis to all trans retinal.
o Causes conformational change in rhodopsin protein.
o Each rhodopsin molecule contains a covalently attached chromophore,
11-cis retinal, which isomerizes almost instantaneously to all-trans retinal
when it absorbs a single photon. The isomerization alters the shape of the
retinal, forcing a conformational change in the protein (opsin). The
activated rhodopsin molecule then alters the conformation of the G protein
transducin (Gt), which causes the activation of cyclic GMP
phosphodiesterase. The phosphodiesterase then hydrolyzes cyclic GMP,
so that cyclic GMP levels in the cytosol fall. This drop in cyclic GMP
concentration decreases the amount of cyclic GMP bound to the plasma
membrane cation channels.
• Fig 15-6B GPCRs:
o Causes change in G protein Gt, t is = transduction.
o Causes activation of cyclic GMP. it’s not causing to be made, it’s going to
activate something inside there.
▪ Phosphodiesterase = enzyme.
▪ Enzyme destroys cGMP.
• Fig 15-37 Cyclic GMP (cGMP)
o Made by guanylyl cyclase.
o Destroyed by cGMP phosphodiesterase.
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Document Summary
Fig 15-6b gpcrs, extracellular signal = light, fig 3-53a retinal, retinal isomerization, retinal isomerization (wikipedia, light causes changes from 11-cis to all trans retinal, causes conformational change in rhodopsin protein, each rhodopsin molecule contains a covalently attached chromophore, 11-cis retinal, which isomerizes almost instantaneously to all-trans retinal when it absorbs a single photon. The isomerization alters the shape of the retinal, forcing a conformational change in the protein (opsin). The activated rhodopsin molecule then alters the conformation of the g protein transducin (gt), which causes the activation of cyclic gmp phosphodiesterase. The phosphodiesterase then hydrolyzes cyclic gmp, so that cyclic gmp levels in the cytosol fall. In the dark: high cgmp > channels are open, cell depolarized, high rates of transmitter release, transmitter inhibits postsynaptic neurons. In the light: destruction of cgmp, channels close, cell hyperpolarizes, transmitter release decreases, activated rhodopsin, cation channels close, and transmission stops, signals to brain = light!
