1.4.4.2 the vertebrate eye Flashcards
what is the retina
the area within the eye that detects light and contains two types of photoreceptor cells
what are the two photoreceptor cells in the retina
rods and cones
what are rods
these are cells that function in dim light but do not allow colour perception
what are cones
these are responsible for colour vision and only function in bright light
what are combined to form the photoreceptors of the cell
retinal and opsin
what is retinal
light sensitive molecule
what is opsin
membrane protein
what is the retinal opsin complex called in rod cells
rhodopsin
what does retinal absorb
a photon of light
how does rhodopsin change conformation
when retinal absorbs a photon of light
what is rhodopsin called after conformation
photoexcited rhodopsin
what does photoexcited rhodopsin activate
a g protein called transducin
what does transducin activate
the enzyme phosphodiesterase
what is PDE
phosphodieterase
how many molecules of g protein are activated by a single photoexcited rhodopsin
hundreds
how is the signal amplified
cascade of proteins
what does PDE catalyse
the hydrolysis cyclic GMP
how many cGMP molecules are broken down per second by each PDE molecule
thousands
what does the reduction of cGMP concentration affect
the function of the ion channels in the membrane of rod cells
what does the impact on the function of ion channels in the rod cell membranes result in
the closure of ion channels in the rod cell membrane, which then results in nerve impulses in neurons in the retina
what can a high degree of amplification lead to
rod cells being able to respond to low intensities of light
is it true that in cone cells different forms of opsin combine with retinal to give different photoreceptor proteins, each with maximal sensitivity to specific wavelengths, red green or blue or UV
yes
In cone cells, different forms of opsin combine with retinal to give
different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths
