Question

Which of the following occurs in photoreceptors when they are exposed to the appropriate wavelength of light?

		Opsin and all-trans retinal combine to form rhodopsin.
		PDE enzyme is activated, which increases cGMP levels.
		Light-gated Na+ channels open, which depolarizes the cell.
		cGMP levels decrease, which closes Na+ channels and hyperpolarizes the cell.

Answer 1

Answer )

a) Opsin and all -trans retinal combine to form rhodopsin.

Others are Incorrect .

Phototransduction mechanism

1)First when light falls it enters Cornea and then through Lens it reaches the Retina and retinal layers .

2)Retina has rods and cones .Rods for dark vision and cones for Colour vision .

3)Now a derivative of Vitamin A,11 cis retinal combine with Opsin to form rhodopsin,pigment in rod cells that is necessary for Vision .

4)After formation of All trans retinal ,transducin get activated by releasing GDP and get converted into activated Transducin with GTP .

5)Activated transducin activate Phosphodiesterases enzyme which is responsibe for degradation of Cyclic GMP .

6)Cyclic GMP is responsible for opened Na+ Channels .

7) Separated opsin produces these reactions timately leads to close some of the Na+ channels, and the result is a hyperpolarizing receptor potential.

8)The action potentials are transmitted to the brain.