Fototransdüksiyon

Fototransdüksiyon is the biochemical process by which light energy is converted into an electrical signal in the eye. This process is fundamental to vision, enabling the detection and interpretation of light. It occurs within specialized photoreceptor cells in the retina, namely rods and cones.

In rods, the primary photopigment is rhodopsin. When a photon of light strikes a rhodopsin molecule, it causes a conformational change in its protein component, opsin, which is bound to a vitamin A derivative called retinal. This change activates a G-protein called transducin. Activated transducin then triggers the activation of phosphodiesterase (PDE). PDE hydrolyzes cyclic guanosine monophosphate (cGMP), a molecule that normally keeps ion channels open.

The reduction in cGMP levels causes these ion channels to close, hyperpolarizing the photoreceptor cell. This hyperpolarization is the initial electrical signal. In cones, the mechanism is similar, involving different photopigments (opsins associated with three different types of retinal) that are sensitive to different wavelengths of light, allowing for color vision.

This hyperpolarization then propagates through a complex network of neurons in the retina, including bipolar cells and ganglion cells, eventually leading to the generation of action potentials in the optic nerve, which transmits the visual information to the brain for further processing and perception of an image.