Microbial Physiology notes lec17 11-3-10

This is essentially irreversible because the external

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This is essentially irreversible because the external pH is low there is always an inside cytoplasm that is more alkaline and more negative than the outside, the outside is more acidic this step is irreversible because of the light input WHY?? 7. Helix 6 (& 7) tilt hydration (becoming more hydrophilic than it was before) of the inner half channel (the conformational change (tilt)decreased contact with external D 85 ; increased contact with internal D 96 ). Inner half channel 8. hydration(more hydrophilic) of D 96 pKa; it becomes an H + donor. 9. The SB is reprotonated from D96 from the inside (SB deprotonation “opens” the inner 1/2 channel). 10. Reversal of the helix 6 tilt restoration of the original pKa of D 96 . This restores the more hydrophobic environment of D 96 ; which is no longer in contact with the SB is lost. 11. D 96 is reprotonated from the cytoplasm. the more hydrophobic environment in the cytoplasm it is more likely that it can acquire a H+ on the inside 12. Retinal undergoes slow thermal reisomerization to all-trans configuration. 2. There are some Rhodopsin which transport Cl - (chloride) a. When they transport chloride, it goes in the opposite direction from the bacterio-rhodopsin transporting H+ out of the cell, and the Cl - is pumped into the cell b. What is the effect of pumping chloride in have on the membrane potential —the energy state of the cell? i. It is exactly the same because you’re pumping the negatively charged chloride in, versus pumping a positively charged proton
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out so the net result in an increase in the membrane potential and an in chloride concentration inside the cell 3. There are homologs of bacterio-rhodopsin which can do a variety if things a. Serving as light receptors for phototaxis there are 2 of these in caulobacteria b. There are also other pigment types c. BUT there are also homologs of bacterio-rhodopsin that don’t serve as an energy source, but instead use the energy source of the membrane potential for folding of proteins these are found in fungi i. So there are chaperone proteins that instead of being driven by ATP hydrolysis which is often the case they are instead driven by light absorption from the rhodopsin
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