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Physiology

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Central Nervous System

Question
18 out of 22
 

transducin protein is seen in


A vision
B hearing

C balance
D smell


Ans. A vision

I. Transducin (Gt) is a heterotrimeric G protein with three polypeptide chains characterized into two subunits: α, β and γ. Transducin is naturally expressed in vertebrate retina rods and cones, with different α subunits in rod and cone photoreceptors.Transducin is a very important G-protein in vertebrate phototransduction.

II. HeterotrimericTransducin is activated by metarhodopsin II, a conformational change in rhodopsin caused by the absorption of a photon by the rhodopsin moiety retinal.

III. The light causes isomerization of retinal from 11-cis to all-trans. Isomerization causes a change in the opsin to become metarhodopsin II.

IV. When metarhodopsin activates transducin, the GDP bound to the α subunit (Tα) is exchanged for GTP from the cytoplasm. The α subunit dissociates from the βγ subunits (Tβγ.)

V. Activated transducin α-subunit activates cGMPphosphodiesterase. cGMP phosphodiesterase breaks down cGMP, an intracellular second messenger which opens cGMP-gated cation channels.

VI. PhosphodiesterasehydrolyzescGMP to 5’-GMP. Decrease in cGMP concentration leads to decreased opening of cation channels and subsequently, hyperpolarization of the membrane potential.

Central Nervous System Flashcard List

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