What is the first molecule formed when rhodopsin absorbs light?

When rhodopsin absorbs light, the first molecule formed is metarhodopsin II. This process begins with the absorption of a photon by 11-cis-retinal, which is a component of rhodopsin. Upon absorption of light, 11-cis-retinal is isomerized to all-trans-retinal. The conformational change in the rhodopsin molecule due to this isomerization activates the visual phototransduction cascade, resulting in the formation of metarhodopsin II, which is the active form of rhodopsin that engages with transducin, a G-protein involved in the signaling pathway.

In essence, metarhodopsin II is crucial because it represents the activated state of the visual pigment necessary for further signal amplification and transmission within the photoreceptor cells. This step is pivotal in the conversion of the light signal into a biochemical signal that eventually leads to visual perception.