lipid bilayer

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sarahjay8
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lipid bilayer

Post by sarahjay8 » Mon Sep 18, 2006 4:38 am

hello I was wondering if any one could help me explain or help me find sources that would explain why the lipid bilayer prevents the diffusion of polar substances. I know its becasue of the hydrophobic effect of the water loving head attacts the polar substances and the hydophilic head repeling it but is there any other reasons?



and another question... I dont expect the answer just some direction!

The pH of a lysosome is 4.8 and the activity of resident acid hydrolases are dependend on this low pH. The key residue for activity of a acid lipase is a histidine in the active site. The histidine must be protonated for the endzyme to be active. If the pKa of histidine is 6.0 what stae does the active site exist in the lysosom, and in a post-Golgi carrier (pH~7.0)? Why? At what pH is the enzyme most active?

thanks

Ultrashogun
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Post by Ultrashogun » Mon Sep 18, 2006 12:48 pm

I cant really tell you at what pH it will work the best, but 50% of the His will be protonated, so at 4.8 more than ten times more will be protonated.

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MrMistery
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Post by MrMistery » Mon Sep 18, 2006 5:44 pm

That is the main reason(the inside of the lipid bilayer is hydrophobic). Other reasons?! I donno. If there are any, they are minor.

Check out the structure of histidine, what happens at different pH values with the side chains. You should be able to solve the problem easily.
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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