Amino Acid: Net Charge

[justadream]

Just want to get this straight:

At pH = 7:

Acidic amino acids are negatively charged.

Basic amino acids are positively charged except for histidine which is negatively charged (since it has pKa of side chain = 6.1)?

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[wuhsabee]

That's correct!

 

[DaAlienist]

I was wondering for phosphopantothenate in an aqueous solution at physiological pH, why would both the OH's on the phosphate group be deprotonated? I googled the pKa's of the OH groups on the phosphate, and it tells me that pKa1 ~ 2 and pKa2 ~ 7.

If that is true, why does the 2nd OH deprotonate in this case? I didn't know the pKa's, so how can I figure out that both the OH's will be deprotonated?

 

[aldol16]

I know the original post was answered long ago, but nobody seems to have caught that His is actually neutral at pH 7. The C-terminus is deprotonated, the N-terminus is protonated, and the side chain is uncharged, making for a net neutral charge.

 

[aldol16]

I was wondering for phosphopantothenate in an aqueous solution at physiological pH, why would both the OH's on the phosphate group be deprotonated? I googled the pKa's of the OH groups on the phosphate, and it tells me that pKa1 ~ 2 and pKa2 ~ 7.

Note that those values are for phosphoric acid and since this is an anhydride, it may be a little different (I don't know how much).