Back in the late 70-ies of the XIX century in the retina of animalrsquo;s eyes and then in humanrsquo;s scientists have discovered the light-sensitiv

Visual pigments (opsins: rhodopsin and iodopsin)

Back in the late 70-ies of the XIX century in the retina of animal’s eyes and then in human’s scientists have discovered the light-sensitive pigments, which become discolored in the light. The rods contain rhodopsin (from Greek “a rose” and “a vision”), and cones — iodopsin (diagram 175). Both pigments are high molecular weight compounds that consist of oxidized vitamin A — retinal and opsin protein.

In the darkness rhodopsin and iodopsin are in an inactive form. Under the influence of light, they decompose (“fade”) and switch to the active form: retinal cleaves from the opsin. As a result, the photoreceptors excite. A nerve impulse occurs. In the darkness the visual pigments recover due to the merge of vitamin A (retinal) with opsin. Lack of vitamin A in the diet causes frustration of chopsticks and a violation of dusky view — the "night blindness": human almost cannot see anything in the evening, and the day sight is functioning normally. That is why it is important to eat foods containing vitamin A. Taken from

Diagram 175. The photosensitive pigment rhodopsin (a) and its transformations (b) under the action of light and in darkness
  • What is the day and the dusky vision?