How Light Bleaches Rhodopsin

For this exercise, you will take a scenario of bleaching occurring within the rod cells and rank the steps in the process from beginning to end.

Rank the order of the bleaching process from beginning to end.

1 - Vitamin A from the bloodstream replenishes what is lost. The vitamin A returns to its original shape and gets reincorporated into rhodopsin.

2 - Rhodopsin absorbs light, and the vitamin A changes shape.

3 - Vitamin A detaches from the rhodopsin, and some vitamin A is lost.

4 - Light travels to the macula within the retina.

5 - Light enters the eye through the cornea.

Light contacts the eye.--------------- Light-absorbing capabilities of proteins are regenerated

Light enters the eye through the cornea.
Light travels to the macula within the retina.
Rhodopsin absorbs light, and the Vitamin A changes shape.
Vitamin A detaches from the rhodopsin, and some vitamin A is lost.
Vitamin A from the bloodstream replenishes what is lost. The vitamin A returns to its original shape.

Explanation:

Retina is the part of the eye that contains photosensitive cells that capture light and produce the electrical signals that the brain perceives as images. These photosensitive cells are of two kinds:

Rods
Cones

Rods contain the photosensitive pigment, rhodopsin that is needed for vision at night or in dim light. Cones function in bright light.

Rhodopsin Bleaching:

Vision in bright or excessive light requires a process called rhodopsin bleaching which is the degradation of rhodopsin upon exposure to light. Upon contact with light, rhodopsin goes through structural changes characterized by the conversion of a pigment derived from Vitamin A, 11-cis retinal to all trans retinal. This chemical conversion initiates a photo-transduction reaction (reaction in which a photon of light is converted into electrical signals) that produces the electrical signals that travel to the brain via the optic nerve. The brain converts the electrical signals to images. This is followed by rhodopsin regeneration in the dark in which all trans retinal is converted back into 11 cis retinal.