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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?
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?
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?
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?
Light induces what in light receptor cells?
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+

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