Serkan: Created page with "'''Retinene''' (/rɛtɪˈniːn/; from Latin ''rete'', "net") is a historical biochemical term for '''retinal''', an aldehyde form of vitamin A that is essential for vision. It is a light-sensitive molecule, or chromophore, found in the photoreceptor cells of the retina. When bound to opsin proteins, retinene forms the visual pigments (like rhodopsin) that absorb photons of light, initiating the cascade of events that results in a nerve impulse to the brain. The term "re..."

2025-06-20T19:17:26Z

Created page with "'''Retinene''' (/rɛtɪˈniːn/; from Latin ''rete'', "net") is a historical biochemical term for '''retinal''', an aldehyde form of vitamin A that is essential for vision. It is a light-sensitive molecule, or chromophore, found in the photoreceptor cells of the retina. When bound to opsin proteins, retinene forms the visual pigments (like rhodopsin) that absorb photons of light, initiating the cascade of events that results in a nerve impulse to the brain. The term "re..."

New page

'''Retinene''' (/rɛtɪˈniːn/; from Latin ''rete'', "net") is a historical biochemical term for '''retinal''', an aldehyde form of vitamin A that is essential for vision. It is a light-sensitive molecule, or chromophore, found in the photoreceptor cells of the retina. When bound to opsin proteins, retinene forms the visual pigments (like rhodopsin) that absorb photons of light, initiating the cascade of events that results in a nerve impulse to the brain.

The term "retinene" was used by early 20th-century researchers, including Nobel laureate George Wald, to describe the pigments they isolated from the retina. Modern chemical nomenclature prefers the term '''retinal''' to reflect the molecule's aldehyde functional group.

== Forms of Retinene ==
The original definition of retinene encompassed two primary forms, now known as retinal₁ and retinal₂:

# '''Retinene₁ (Retinal):''' This is the most common form, found in the eyes of most mammals, birds, reptiles, and marine fish. Its chemical structure is derived from retinol (vitamin A₁). In the visual cycle, it exists as '''11-cis-retinal''' in its light-sensitive, pre-activation state.
# '''Retinene₂ (3,4-dehydroretinal):''' This form is primarily found in the retinas of freshwater fish and some amphibians. It is derived from vitamin A₂ (3,4-dehydroretinol) and differs from retinal₁ by having an extra double bond in its carbon ring. This structural difference shifts its light absorption maximum to longer wavelengths, an adaptation to the reddish light environment of freshwater habitats.

== Function in Vision ==
Retinene is the fundamental molecule that allows the eye to detect light. Its function is central to the '''visual cycle''':

# '''Pigment Formation:''' In the dark, the bent isomer of the molecule, '''11-cis-retinal''', is bound to a protein called '''opsin'''. This combined molecule is a visual pigment. In the rod cells, this pigment is called '''rhodopsin'''.
# '''Photoisomerization:''' When a photon of light strikes the rhodopsin molecule, it provides the energy for the 11-cis-retinal to straighten into its linear form, '''all-trans-retinal'''.
# '''Activation and Signaling:''' This change in the shape of retinene forces a conformational change in the opsin protein. The activated opsin then triggers a biochemical cascade (the phototransduction cascade) within the photoreceptor cell, which culminates in an electrical signal being sent to the brain.
# '''Recycling (Bleaching):''' After activation, the all-trans-retinal no longer fits in the opsin protein and separates from it—a process known as "bleaching." To restore vision, the all-trans-retinal must be converted back to 11-cis-retinal and re-bound to opsin. This recycling process involves enzymes that convert all-trans-retinal to all-trans-retinol (the alcohol form of vitamin A) and then back to 11-cis-retinal.

== Relationship to Vitamin A ==
Retinene (retinal) is a key component of the vitamin A family of compounds, known as retinoids.

* '''Precursors:''' The ultimate dietary precursors of vitamin A are carotenoids, such as beta-carotene, found in plants. The body cleaves beta-carotene to produce retinal.
* '''Interconversion:''' Retinal exists in a metabolic balance with '''retinol''', the alcohol form of vitamin A. Retinol is the storage form of the vitamin, and it can be oxidized to form retinal when needed for vision. This conversion is reversible.
** Retinol⇌Retinal
* '''Deficiency:''' A dietary deficiency in vitamin A leads to a shortage of retinal in the retina. This impairs the ability to regenerate visual pigments, especially rhodopsin in the rods, resulting in '''night blindness'''.

[[Category:Medical Terms]]

Retinene - Revision history