Team:SDU-Denmark/project-t

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(Retinal requirements of light-sensing proteins)
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== Retinal Generator ==
== Retinal Generator ==
====Retinal requirements of light-sensing proteins====
====Retinal requirements of light-sensing proteins====
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Proteorhodopsins and other related light-sensing proteins such as the rhodopsins found in human retinal pigment often require a supply of retinal to function. In fact retinal is the molecule responsible for the initial activation, as it undergoes photoizomerization after being struck by a photon. It is this change in conformation of the retinal molecule that is relayed through the entire rhodopsin-transducer complex to activate/deactivate the CheW/A complex in the cytosol. Thus either an external supply of retinal or an internal supply, generated by means of genes coding for enzymes in the retinal biosynthesis pathway are required, if we wish to see phototactic behaviour in our cells.<br><br>
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Proteorhodopsins belong to a group of molecules consisting of a protein called an opsin with a cromophore(usually a retinal enantiomer) attached as a prosthetic group. The retinal chromophore is the molecule responsible for the initial light-activation, as it undergoes photoizomerization after being struck by a photon. It is this change in conformation of the retinal molecule that is relayed through the entire rhodopsin-transducer complex to activate/deactivate the CheW/A complex in the cytosol. Thus either an external supply of retinal or an internal supply, generated by means of genes coding for enzymes in the retinal biosynthesis pathway are required, if we wish to see phototactic behaviour in our cells.<br><br>
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Many plants and microbes have complete retinal biosynthesis pathways in their genomes, to help drive their rhodopsins. In these organisms rhodopsins play an essential role, not only for photosensing but also directly in energy production. In fact in some organisms rhodopsins are used to create proton motive force directly by pumping protons out into the extracellular space using light energy to drive the process. Humans and other animals on the other hand often only have enzymes coding for the final steps of the pathway, more on which later. They rely on a supply of retinal precursors or vitamin A (a group of molecules consisting of retinal and it's metabolites) in their diet. This is why vitamin A deficiency causes night-blindness as an early symptom in humans.<br><br>
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These light-sensitive pigments can be found in a large variety of organisms from archaea and bacteria to both uni- and multicellular eukaryotes. Many plants and microbes have complete retinal biosynthesis pathways in their genomes, to help drive their rhodopsins. In these organisms rhodopsins play an essential role, not only for photosensing but also directly in energy production. In fact in some organisms rhodopsins are used to create proton motive force directly by pumping protons out into the extracellular space using light energy to drive the process. Humans and other animals on the other hand often only have enzymes coding for the final steps of the pathway, more on which later. They rely on a supply of retinal precursors or vitamin A (a group of molecules consisting of retinal and it's metabolites) in their diet. This is why vitamin A deficiency causes night-blindness as an early symptom in humans.<br><br>
==== Retinal biosynthesis ====
==== Retinal biosynthesis ====

Revision as of 21:11, 26 October 2010