Average fitness

In a species, only 1 of every 1000 seeds survives to reproductive age, and that those that survive produce an average of 3000 seeds.

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#XL - T Zoology

The heterotrimeric G protein coupled to rhodopsin, called transducin (Gt)

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#Id: 9304

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In the absence of light,  bound 11-cis-retinal locks the rhodopsin into its inactive (R) conformation

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#Id: 9305

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Absorption of light causes rapid photoisomerization of the bound cis-retinal to the all-trans isomer, triggering a conformational change in opsin that activate the Gαt.

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#Id: 9306

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There are about 90 million rod cells in the human retina, and each contains about 4x107 molecules of rhodopsin that are very densely packed in the membrane disks.

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#Id: 9307

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A single activated rhodopsin protein activates 

~13 transducin molecules in the few seconds before the covalent bond between the opsin protein and all-trans-retinal is spontaneously cleaved

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#Id: 9308

#XL - T Zoology

RPE65 is the enzyme in the pigment epithelial cells of the retina that catalyzes the isomerization of the intermediate esterified all-trans retinol to 11-cis-retinol.