nov.12 pt4 Flashcards
what happens when light hits outer segment of photoreceptor?
change in RMP
RMP of photoreceptor cell
minus forty mV
light causes __ in membrane of photoreceptor cells
HYPERPOLARIZATION
example of change in RMP in photoreceptor cells
minus 40mV to minus 65mV
cGMP gated channels of photoreceptor cells are ____ when its dark
open
advantage of metabtropic receptors in photoreceptors
amplification
three steps of PHOTOTRANSDUCTION
- activation of visual pigment ie photoreceptor by light 2. activated photopigment triggers biochemical signalling pathway leading ot reduction of cGMP 3. closure of cGMP gated channels and hyperpolarization
cGMP gated channels are
nonselective cation channels
reversal potential of the cGMP gated channels
0
photopigment consists of
opsin and vitamin A aldehyde AKA 11-cis retinal
opsin is this type of protein
GPCR
opsin is covalently linked to
lysine
opsin is light sensitive when
attached to 11-cis retinal
light has this effect on rhodopsin
conformational change to 11-trans retinal, triggering conformation change in opsin
what happens to retinal after photoisomerization
dissociate from opsin, transported out of photoreceptor cells, taken up into epithelial cells, converted back to 11-cis retinal, and transported back
when GTP binds alpha subunit of G protein
alpha dissocaites from beta gamma, g alpha then activates PDE, hydrolyzing cGMP to GMP
all events leading to cGMP hydrolsis occurs in
membranes of disks
result of PDE activation
reduce cyto conc of cGMP, cGMP-gated channels close
