Flashcards in Photoreception and Transduction Deck (72):
What is the visible spectrum?
400nm - 700nm
Why is the sky blue?
Blue light is scattered more than any other color because it has the shortest wavelength of any color we can see
Cones start to respond to light around _____ photons/cone/second and can extend up to _____ photons/cone/second
3 photons per cone per second
1 million photons/cone/second
Anatomically, rods are ____ than cones are lie ____ in the RPE
deeper in the RPE
In humans, there are ____ rods for every cone
True/False. More peripheral cones looks like rods
What role do cilia play in photoreceptors?
Support for the connection between the outer and inner segment layers
Visual transduction takes place in the _______
outer segment of photoreceptors
What are the two parts of the inner segment of visual cells?
Ellipsoid and Myoid
What is the Ellipsoid part of a photoreceptor?
outer part of the inner segment. Contains Mitochondria
What is the Myoid part of a photoreceptor?
inner part of the Inner segment part. Contains organelles and tubules
Where is the cell body of a photoreceptor located?
Outer nuclear layer (think nucleus = nuclear layer)
How is the cell body of a photoreceptor connected to the inner segment?
Out receptor fiber
What is the spherule?
the synaptic end of the rod and cone
In rods, the spherule is ______ while in cones, the spherule is ______
rod - rounded
cone - pyrimadal
a rod outer segment contains _____ while a cone outer segment contains _____
There are no rods in the _____
What is the peak sensitivity of a rod?
True / False. Sensitivity of light in photoreceptors is due to pigment sensitivity
FUCK NO! Rod and Cones have the same pigment sensitivity.
What % of photoreceptors are cones?
foveal cones are ______ than peripheral cones
foveal cones are smaller
Rod sensitivity to light is due to what?
CONVERGENCE of light information from multiple rods onto single retinal bipolar cells
What is the peak sensitivity of Long-wavelength cones?
what is the peak sensitivity of medium-wavelength cones?
what is the peak sensitivity of short-wavelength cones?
what is the peak sensitivity of UV-sensitive cones?
355 - 440 nm. NOT IN HUMANS mothafucka
How are blue cones different from other cones?
1. shape similar to rods
2. mainly in parafoveal region
3. amino acid sequence similar to rods
All photopigments are forms of ______
What is the fourth opsin that is thought to play a role in the control of the circadian rhythm?
What are the three photopsins in order of increasing wavelength?
Cyanolabe - blueish violet
Chlorolabe - green
Erthyrolabe - yellowish red
What make up photopigments?
Proteins (opsin) + Chromophore
What is chromophore derived from?
How is the chromophore joined to the opsin?
Rhodopsin is how many amino acids long?
S-cone opsins are how many amino acids long?
346 - 350
L/M opsins are how many amino acids long?
The additional length of the L/M opsins can be found at what region of the protein?
the N - terminal
What is found at Position 296 on the photopigment chain?
e- amino group of lysine residue which provides the link between opsin and chromophore
What is found at Position 291 on the photopigment chain?
Binding pocket for chromophore
What is Positions 110 and 187 on the photopigment chain?
critical for folding
L and M cones are found on what gene?
X - chromosome
All mammalian photopigments have what type of chromophore?
What is an opsin shift?
Any pigment that has a peak sensitivity different from 440 nm
In porphyropsin, the chromophore is the aldehyde of ______
In rhodopsin, the chromophore is the aldehyde of ______
What spectral tuning sites account for the majority of rod and cone sensitivity changes?
T285A and Y277F
Where would you find porphyropsin?
Fresh water fish
What's the difference between rhodopsin and porphyropsin?
rhodopsin - shorter Vmax
Porphyropsin - longer Vmax
What happens in the light reaction?
Light causes 11-cis retinal (bent form) to change to all-trans retinal (straight form)
What event triggers transduction?
the formation of metarhodopsin II
The reactions that occur before the formation of meta II are ______ by ______
reversible by blue light
Why is blue light the only way to reverse the light reaction?
it is the only color that has enough energy to cause the reformation of the bend of the molecule
What happens 10 minutes after meta II is formed?
chromophore is released
What happens 20 minutes after meta II is formed?
rhodopsin is formed
What is "the fit" in a dark reaction?
Change in spectral peak with change in conformration of the chromophore and protein
What are the three peaks for Rhodopsin?
alpha peak - visible range
What is the beta peak?
bond between opsin an chromophore. 350 nm
what is the gamma peak?
bond between tyrosin and tryptophan. not seen by humans
What is transduction?
the transformation of light into electrical and chemical signals that produce the perception of light
what is photoreception?
photon absorbed by visual pigment that is lying on one of the discs in the outer segment
what is the biochemical cascade?
in light, the pigment molecule is activated and the ion channels close
what is the electronic spread?
after the ion channels close, there is a buildup of positive charge on the outside of the photoreceptor making it hyperpolarized
what is synaptic deactivation?
the concentration of calcium decreases, leading to a decrease in the release of glutamate
Explain how the G protein is activated by Rhodopsin:
1. ______ runs into an inactive G molecule
2. the _____ part sits on top of Rhodopsin
3. ____ replaces GTP
4. ______ separates from the G molecule
1. *Rhodopsin* runs into an inactive G molecule
2. the *G alpha* part sits on top of Rhodopsin
3. *GDP* replaces GTP
4. *G alpha unit* separates from the G molecule
Explain how the G protein combines with cGPDE:
1. Activated G protein binds with _____
2. This molecule converts ____ into GMP
3. cGMP concentration lowers, ____ close
1. Activated G protein binds with *PDE*
2. This molecule converts *cGMP* into GMP
3. cGMP concentration lowers, *ion channels* close
What causes the hyperpolarization during electronic spread?
K+ ions are moving out of the cell even after the channels close due to lower cGMP concentration. Produces a positive charge on the outside of the photoreceptor because Ca+ and Na+ no longer move in
A single photon isomerization will close ion channels and cause a ___% reduction in the photocurrent
The rod photocurrent causes a ____ change in current and lasts ____ or more
34 pA change for 600 ms or more
Photocurrent in cones is ____ the rod response and the duration is _____
1/20th. Much shorter
Photocurrent in cones is ______ as opposed to _____ in rods
biphasic as opposed to monophasic
What is light adaptation controlled by?