M1-C2-L32 --> Vitamin A and Phototransduction
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- In the phototransduction visual cycle, 11-cis retinal is converted to what?
- All trans isomer by visible light.
- What is the major retinoid hormone of the body?
- Retinoic Acid
- Retinoic Acid is the ligand for what?
- Nuclear hormone receptors modulating transcription.
- Dietary retinol is carried as _______ in _____________
-
retinyl esters
lymph chylomicrons - Absorbed beta-carotene is carried in?
- Chylomicrons
- Vitamin A is solube in what type of compound?
- Fat soluble
- Retinoid receptors are similar to what other type of receptors?
- steroid hormone
- What type of cells specially benefit from Retinoic acid?
- Epithelial
- All-trans retinoic acid (tretinoin) is useful in what medically?
- A variety of dermatalogical conditions such as psoriasis
- 13-cis retinoic acid (isotretinoin) is used to treat what?
- Severe acne
- What are the complications of 13-cis retinoic acid (isotretinoin)?
- It is a teratogen. Contraindicated in pregnant women or women with childbearing potential.
- What is the major function of vitamin A?
- Phototransduction
- What are light sensitive neurons called that detect light?
- The rods and cone cells
- What are the functions of rod cells and describe their quantity.
-
Most numerous.
Very sensitive to light. Critical for vision in dim light. - What are the functions of cone cells and describe their quantity.
-
Very few.
Little light sensitivity, but can discriminate color. - Describe the similar structure of rods and cones.
-
Inner segment w/ nucleus and mitochondria
Outer segment with stacks of membranous containing opsin proteins - What are opsin proteins and what is their function.
-
Light receptors in the signal transduction process.
Located on the outer segment in stacks of membranous disks. - What is Rhodopsin?
- Rod cell light receptors
- What is transducin?
- Trimeric G-protein of phototransduction
- Rhodopsin and transducin are anchored to membrane by what?
- C-terminal lipid modifications
- What is the second messenger in visual receptor cells?
- cGMP
- Light induces what in light receptor cells?
- Hyperpolarization
- Describe the transmembrane potential of the inner segment when in the dark.
- Low potential produced by Na-K ATPase
- When rhodopsin absorbs light, it does what to cGMP?
- Hydrolyze them
- Hydrolysis of cGMP does what to cation channels?
- Closes them, thus hyperpolarization b/c Na-K ATPase continues to generate electric signal
- Discrimination of colors and hues is accomplished by integrating output from what?
- Three types of cone cells.
- Differences in cone cells are seen where?
- Amino acid differences in the retinal binding site.
- If gene rearrangement occurs BETWEEN transcribed regions, then what is the result.
- Difficulty distinguishing red and green
- In gene rearrangement occurs WITHIN transcribed regions, then what is the result?
- Difficulty discriminating color.
- Vitamin A deficiency causes what?
- Nyctalopia (poor night vision)
- No vitamin A causes what? x3
-
Xeropthalmia - no tears
Keratomalacia - dry cornea
Corneal erosion - Hyperpolarization occurs by blocking what channels?
- Na+ and Ca2+