User:Emmasomerville/sandbox

OPN1LW

Intro?
OPN1LW is a gene that encodes for long wave sensitive opsin 1. The protein absorbs light between the wavelengths of 500-570nm, with peak absorption being around 560nm. Long wave sensitive (LWS) opsin is also know as red cone opsin or pigment, as it is the the most sensitive to red light out of the three cones types.

Gene
OPN1LW is just one of the genes contributing to human colour vision. OPN1LW produces red-sensitive opsin, while it's counterparts, OPN1MW and OPN1SW, produce green-sensitive and blue sensitive opsin respectively. OPN1LW and OPN1MW are both on the X-chromosome at position Xq28. They are in a tandem array, composed of a single OPN1LW which is followed by one or more OPN1MW genes. The locus control region (LCR) regulates expression of both genes, with only the OPN1LW gene and nearby adjacent OPN1MW genes being expressed and contributing to the colour vision phenotype. The LCR can not reach OPN1MW genes that are 3 or more genes away. OPN1LW and OPN1MW have similar, but slightly different absorption patters. The slight shift in their respective cone spectral ranges is due to a few amino acid differences between the two genes.

Protein
The LWS type I opsin is a G protein-coupled receptor (GPCR) with embedded 11-cis retinaldehyde. It is a transmembrane protein that has seven membrane domains, with the N-terminal being extracellular and the C-terminal being cytoplasmic. The LWS pigment has a max absorption of about 560, with an absorption range of 500-570.

Evolutionary History
Before trichromatic vision came to be, dichromatic vision consisted of simply OPN1LW and OPN1SW. OPN1LW is thought to have undergone a duplication event that lead to an extra copy of the gene, which then evolved independently to become OPN1MW. OPN1LW and OPN1MW share 98% of their DNA sequences, whereas OPN1LW and OPN1SW share only 40%. This is strong evidence for the duplication theory. The emergence of OPN1MW is directly associated with evolution from dichromacy to trichromacy. The presence of both LSW and MSW opsins improves colour recognition time, memorization for coloured objects, and distance-dependent discrimination, giving trichromatic individuals an evolutionary advantage when searching for nutrient rich food sources.