Animal vision evolved 700 million years ago

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Gaze deep into any animal eye and you will find opsin, the protein through which we see the world. Every ray of light that you perceive was caught by an opsin first. Without opsin there would be no blue, no red, no green. The entire visible spectrum would be.. just another spectrum.


But opsins haven’t always been the sensitive light detectors that they are today. There is one critter, obscure and small, carries opsins that are blind to light. These opsins aren’t broken, like they are in some cave dwelling species. They never worked to begin with. They are the relics of a distant past, a time in which our ancestors still dwelt in darkness.

Opsin is a member of large family of detector proteins, called the ‘G-protein coupled receptors’ (GPCRs). Like a needle and thread, all GPCRs wind themselves through the outer membrane of the cell seven times. Halfway between cell and outside world, these tiny sensors are perfectly positioned to monitor the surroundings of the cell. Most GPCRs detect the presence of certain molecules. When a certain hormone or neurotransmitter docks their outward facing side they become activated and release signalling molecules on the inside of the cell. But opsin is different. It doesn’t bind molecules physically. Instead, it senses the presence of a more delicate and ephemeral particle: the photon itself, the particles (and waves) that light is made of.

Opsins trap photons with a small molecule in the heart of their architecture, called retinal. In its resting state retinal has a bent and twisted tail. But as soon as light strikes retinal, its tail unbends. This molecular stretching exercise forces the opsin to change shape as well. The opsin is now activated and eventually will cause a nearby nerve to fire, which will relay its message to the brain: light!.

Written By: Lucas Brouwers
continue to source article at blogs.scientificamerican.com

5 COMMENTS

  1. The eyes seem the ‘focal’ points of  the ‘god-must-have-dunnit-its-too-bloody-complex’ so this research is indeed brilliant. There is little chance for debate or change with some of these folks, so I shall mumble ‘opsin!’ ‘opsin!’ to myself as I grow old; smug, immature and gleefully childish as I cane past the local shrines, in this sweet knowledge of how things really work. Bliss.

  2. PY –
      There is little chance for debate or change with some of these folks, so I shall mumble ‘opsin!’ ‘opsin!’ to myself

    The eye has evolved many times into independent forms (camera eyes, compound eyes etc) , and it seems opsins have also evolved more than once.

    In his book Life’s Solution, Conway-Morris made the case for a semblance of predictability in evolution.
    He argued that convergence – the independent origin of similar traits – represents an element of predictability in evolution.
    Octopus and humans have outwardly similar eye designs, so if we reply animal history over and over, these camera-type eyes would likely evolve in most replays.

    Here I’ll describe a truly amazing molecular convergence that was not discussed by Conway-Morris: the independent evolution of opsin proteins (a protein responsible for light perception) in two different groups of organisms. It turns out that a
    7-transmembrane protein (opsin), bound to a light reactive chemical on the 7th transmembrane domain, has evolved twice to sense light!

    If we could go back a few billion years and replay the evolution of life on earth a few times, chances are, opsins would evolve in many of our replicates. -  http://evolutionarynovelty.blo

    Type I and Type II opsins
    Two major classes of opsins are defined and differentiated based on primary protein sequence, chromophore chemistry, and signal transduction
    mechanisms. Several lines of evidence indicate that the two opsin classes evolved separately, illustrating an amazing case of convergent evolution. 

    http://2.bp.blogspot.com/_x4a1

  3. I am delighted to see how deep runs our current understanding of the molecular machinery of life.  Convergent evolution is apparent in things like birds and bats,  fish and dolphins etc, but it’s fascinating to see it also at the molecular level.

    This has the downside – for me – of suggesting that those cheap sci-fi shows had it right all along – aliens, when we finally meet them, will turn out to look like actors in funny suits and makeup.  I’d been hoping for something more exotic.  How disappointing.

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