Term
| Which protein acts as the receptor of photons? |
|
Definition
|
|
Term
| When it receives a photon, what does Rhodopsin activate? |
|
Definition
| It activates the G-protein Transducin |
|
|
Term
Name the 6 main classes
of cells found in the retina |
|
Definition
Rods
Cones
Horizontal
Bipolar
Amacrine
Ganglion cells |
|
|
Term
| What type of receptor is Rhodopsin? |
|
Definition
| A G-protein coupled receptor |
|
|
Term
| What are the 2 major groups of Opsins? |
|
Definition
R-opsins, rhabdomeric
C-opsins, ciliary |
|
|
Term
| What color of light does rhodopsin absorb the most? |
|
Definition
| Green (wavelengths ~500nm) |
|
|
Term
| Which color of light are r-opsins insensitive to? |
|
Definition
|
|
Term
| In the amino acid sequence of rhodopsin, what amino acid does 11-cis-retinal bind to? |
|
Definition
|
|
Term
| Which rhodopsins are scotopsins and which are photopsins? |
|
Definition
Rod rhodopsins are scotopsins
Cone rhodopsins are photopsins |
|
|
Term
| Which protein is involved in Retinitis Pigmentosa? |
|
Definition
| A mutation in Rhodopsin causes Retinitis Pigmentosa |
|
|
Term
| Describe the 'movement' of the subunits when transducin is activated. |
|
Definition
| The beta and gamma subunits fall off, leaving the remaining alpha subunit as the activated part. |
|
|
Term
| What does the activated alpha subunit of transducin do? |
|
Definition
| It binds to and activates Phosphodiesterase (PDE) |
|
|
Term
| What does Phosphodiesterase do in the visual cycle? |
|
Definition
| Phosphodiesterase hydrolyzes cGMP to GMP, which closes the cGMP gated channels |
|
|
Term
| Explain how the closure of cGMP gated channels affects the cells voltage |
|
Definition
| The closure of these channels disrupts the dark current and results in hyperpolarization of the cell. |
|
|
Term
Compe phosphorylated Rhodopsin (Rh*-P) to
phosphorylated rhodopsin bound to arrestin (Rh*-P-Arr) |
|
Definition
Rh*-P retains partial activity
Rh*-P-Arr is fully inactive |
|
|
Term
| What does 11-cis-Retinal isomerize to when a photon is absorbed? |
|
Definition
|
|
Term
| What does Rhodopsin get converted to before it activates Transducin? |
|
Definition
|
|
Term
| How many subunits does phosphodiesterase have and what are they? |
|
Definition
4
Alpha
Beta and two gamma |
|
|
Term
| Explain how GDP and GTP are involved in the activation of transducin |
|
Definition
| When metarhodopsin II activates Transducin, not only do the beta and gamma subunits fall off but GDP is exchanged for GTP, producing G-alpha-GTP |
|
|
Term
| Explain the movement of subunits of transducin and phosphodiesterase in the process of activating phosphodiesterase |
|
Definition
When activated the beta and gamma subunits of Transducin-GDP fall off, leaving alpha-GTP.
2 alpha-GTP bind to the 2 gamma subunits of phosphodiesterase, which are inhibitory.
This causes the release of the alpha and beta subunits of phosphodiesterase, thus removing their inhibition.
They then catalyze the hydrolysis of cGMP. |
|
|
Term
| Describe the 2 levels of deactivation of rhodopsin |
|
Definition
1. Receptor kinase phosphorylates Rhodopsin
2. Arrestin interacts with the phosphate group and interrupts interaction between Rhodopsin and Transducin. |
|
|
Term
| What functional groups bind to the phosphate group in deactivation of rhodopsin? |
|
Definition
| Serine and Threonine allow the phosphate to bind to rhodopsin |
|
|
Term
| How does Calcium affect the receptor kinase (RK) |
|
Definition
| High levels of calcium inhibit the receptor kinase, stopping it from phosphorylating and subsequently deactivating rhodopsin. |
|
|
Term
| How do high levels of calcium affect rhodopsin activity? |
|
Definition
| High calcium levels prevent deactivation of rhodopsin. |
|
|
Term
| How do low levels of calcium affect rhodopsin |
|
Definition
| Low levels of Calcium allow the receptor kinase to work and desensitize rhodopsin |
|
|
Term
| How is transducin deactivated? |
|
Definition
The alpha subunit of Transducin has its own GTPase.
Thus it can convert the G-alpha-GTP to G-alpha-GDP (dephosphorylated form)
Once this occurs, the beta and gamma subunits return, forming inactive transducin. |
|
|
Term
| What is the rate limiting step in the deactivation of Transducin? |
|
Definition
| The action of the GTPase which removes one phosphate from the alpha subunit, to form alpha-GDP. |
|
|
Term
| How is phosphodiesterase deactivated? |
|
Definition
| The 2 gamma subunits return to the alpha and beta subunits |
|
|
Term
| Are the cGMP-gated cation channels specific or non-specific. |
|
Definition
| Non-specific, they will let any cation through |
|
|
Term
| cGMP gated channels are (blank) in the dark and (blank) in the light |
|
Definition
Blank 1- Open
Blank 2- Closed |
|
|
Term
Ca2+ carries how much of the dark current?
What carries the rest of it? |
|
Definition
| Ca2+ carries 15% of the dark current and Na+ carries the rest of it. |
|
|
Term
| What molecule modulates the activity of the receptor kinase in response to Calcium? |
|
Definition
|
|
Term
| What molecule makes cGMP from GTP? |
|
Definition
|
|
Term
| How does Calcium affect the activity of Guanylate Cyclase? |
|
Definition
High calcium inhibits Guanylate Cyclase
Low calcium allows GC to be active and produce cGMP |
|
|
Term
| How does calcium affect the CNG channels? |
|
Definition
| A decrease in calcium leads to an increase in affinity of CNG channels for cGMP |
|
|
Term
| Describe 3 roles of Calcium in the visual pathway |
|
Definition
1. A decrease in calcium activates the receptor kinase
2. Decrease activates GC
3. Decrease increases the affinity of CNG channels for cGMP |
|
|
Term
| How does calcium affect cGMP levels? |
|
Definition
High calcium inhibtis GC, thus decreasing levels of cGMP
Low levels activate GC, increasing levels of cGMP |
|
|
Term
| Which is faster, rods or cones? |
|
Definition
| Cones have faster activation and recovery |
|
|
Term
| Name 2 membrane proteins found in the discs (outer segment) that contribute to structure |
|
Definition
|
|
Term
11-cis-RAL gets converted to all-Trans-RAL,
then what happens to all-Trans-RAL? |
|
Definition
| It gets Reduced to all-trans-ROL |
|
|
Term
| Where does the reduction of all-trans-RAL to all-trans-ROL occur? |
|
Definition
|
|
Term
| What happens to all-trans-ROL once it is formed from all-trans RAL? |
|
Definition
| It gets transported from the photoreceptor into the Retinal Pigment Epithelium cell |
|
|
Term
| What happens to all-trans-ROL once inside the retinal pigment epithelium? |
|
Definition
| Esterification of all-trans-ROL, forming all-trans-R-Ester |
|
|
Term
| What is the next step in the visual cycle after all-trans-R-Ester is formed? |
|
Definition
| It is converted into 11-cis-ROL |
|
|
Term
all-trans-R-Ester --> 11-cis-ROL
What enzyme? |
|
Definition
|
|
Term
| What is the next step in the visual cycle once 11-cis-ROL is formed? |
|
Definition
| 11-cis-ROL is oxidized to 11-cis-RAL |
|
|
Term
| What happens to 11-cis-RAL once it is formed in the RPE cell? |
|
Definition
| Gets transported into the photoreceptor |
|
|
Term
| Where does the oxidation of 11-cis-ROl to 11-cis-RAL occur? |
|
Definition
|
|
Term
| Where does the conversion of All-trans-R-Ester to 11-cis-ROL occur? |
|
Definition
|
|
Term
| Name the 4 forms of Vitamin A discussed |
|
Definition
Retinol
Retinal
Retinoic acid
Retinyl Ester |
|
|
Term
| What functional role does Retinol have? |
|
Definition
|
|
Term
| What functional role does Retinal have? |
|
Definition
|
|
Term
| What functional role does Retinoic acid have? |
|
Definition
|
|
Term
| What functional role does retinyl ester have? |
|
Definition
|
|
Term
| Of the 4 forms of Vitamin A, which one has a role in storage? |
|
Definition
|
|
Term
| Which of the 4 forms of Vitamin A plays a role in transport? |
|
Definition
|
|
Term
Which of the 4 forms of Vitamin A plays a role in Visual
Transduction? |
|
Definition
|
|
Term
| Which of the 4 forms of Vitamin A plays a role in Synthesis |
|
Definition
|
|
Term
| What do RPE cells have the Muller cells do not? |
|
Definition
|
|
Term
| How do cones use Muller cells in the visual cycle? |
|
Definition
| Muller cells can be used to recycle all-trans-ROL back into 11-cis-ROL (instead of this being done in the RPE cell) |
|
|
Term
| Which substance in the visual cycle is involved in Retinitis Pigmentosa? |
|
Definition
|
|
Term
| What part of the visual cycle is involved in Stargardt's disease? |
|
Definition
| Mutation in the gene for ABCA4 |
|
|
Term
| Which part of the visual cycle is involved in Leber's congenital amaurosis? |
|
Definition
|
|
Term
| Describe what can happen if all-trans-RAL accumulates in the RPE cells rather than being recycled properly. |
|
Definition
all-trans-RAL will react with phosphatidylethanolamine to from A2E
A2E then reacts with light to form free radicals which damage the RPE cells |
|
|
Term
Rods are for (blank) resolution
Cones are for (blank) resolution |
|
Definition
Rods-temporal resolution
Cones-spatial resolution |
|
|
Term
| All Rod bipolar cells are ON/OFF (pick one) |
|
Definition
| They are all ON, they depolarize in the presence of light |
|
|
Term
| Name the 2 types of glutamate receptors |
|
Definition
|
|
Term
| Which are faster, metabotropic or ionotropic receptors? |
|
Definition
| Ionotropic receptors are faster |
|
|
Term
| If Metabotropic receptors are G-protein coupled receptors, what are Ionotropic receptors? |
|
Definition
| Ligand gated ion channels |
|
|
Term
| What neurotransmitter is associated with A2? |
|
Definition
|
|
Term
| What neurotransmitter is associated with A17 |
|
Definition
|
|
Term
| What neurotransmitter is associated with A18 |
|
Definition
|
|
Term
| What is the function of A2 cells? |
|
Definition
Transmit signal between
-rod bipolars and ganglion cells (via amacrine)
or
-rod bipolars and cone bipolars |
|
|
Term
| Which types of bipolar cells (ON or OFF) synase in sublamina A |
|
Definition
| OFF cells synapse in sublamina A, which is more outer than B, ie. closer to the RPE |
|
|
Term
| Which layer do the ON bipolar cells synapse in |
|
Definition
| Sublamina B, which is more inner than A, closer to the ganglion. |
|
|
Term
An OFF center cell
Light on the surround only
How will the cell respond? |
|
Definition
| The cell will fire rapidly |
|
|
Term
Have an ON center cell
There is light on center and surround
How will cell respond? |
|
Definition
| There will be a weak response, low frequency firing |
|
|
Term
| Considering Tonic and Phasic Cells, which are for color and which are for movement? |
|
Definition
Tonic are for color
Phasic are for movement |
|
|
Term
| Considering Phasic and Tonic cells, which is similar to Parvo cells and which is similar to Magno |
|
Definition
Tonic cells are similar to Parvo-they 'see' resolution and detail
Phasic cells are similar to Magno -->motion detection |
|
|
Term
|
Definition
| intrinsically photosensitive Retinal Ganglion Cells |
|
|
Term
| How are ipRGCs different from other Ganglion cells? |
|
Definition
| ipRGCs respond to the photopigment Melanopsin |
|
|
Term
| How do ciliary and rhabdomeric pigments differ in their response to light? |
|
Definition
Ciliary pigments result in hyperpolarization due to the presence of light
Rhabdomeric - depolarization in response to light. |
|
|
Term
| Name 3 Mechanisms of photoadaptation |
|
Definition
1. Pupil constriction
2. Photochemicals (hyperpolarization decreases glutamate release)
3. Neural processing-modulation by amacrine and horizontal cells etc.
|
|
|
Term
| Do we adapt faster to dark environments or bright environments? |
|
Definition
| We are faster when adapting to light compared to dark environments. |
|
|
Term
| Name 3 types of non-neuronal cells found in the retina |
|
Definition
1. Muller cells
2. Astrocytes
3. Microglia |
|
|
Term
| What supplies blood to outer retina? |
|
Definition
|
|
Term
| What supplies blood to the inner retina? |
|
Definition
|
|
Term
| How is the majority of glucose consumed in the retina? (Aerobically, anaerobically or PPP) |
|
Definition
| 60% of glucose is consumed anaerobically |
|
|
Term
| What aspect of glucose metabolism plays an important role in the production of antioxidant molecules? |
|
Definition
| The metabolism of glucose via the PPP pathway produces antioxidant molecules. |
|
|
Term
| How is the majority of ATP produced in the retina? (Aerobically or anaerobically) |
|
Definition
| Majority of ATP is produced Aerobically |
|
|
Term
| How can glutamate be incorporated in ATP production in the retina |
|
Definition
| Glutamate can be converted to alpha-ketoglutarate which can then enter the Kreb's cycle. |
|
|
Term
| Name 3 substances that the retina can use to produce ATP in addition to glucose |
|
Definition
Glutamate
Malate
Succinate |
|
|
Term
| Name the 2 most abundant retinal lipids |
|
Definition
Phosphatidylcholine
Phosphatidylethanolamine |
|
|
Term
| What is the major carrier of Vitamin A in the blood? |
|
Definition
|
|
