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Amino Acid: Net Charge

Discussion in 'MCAT Study Question Q&A' started by justadream, Sep 27, 2014.

  1. justadream

    justadream 5+ Year Member

    Apr 29, 2011
    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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  3. wuhsabee

    wuhsabee BEARS. BEETS. BATTLESTAR GALACTICA. 5+ Year Member

    Jul 29, 2011
    That's correct!
  4. DaAlienist


    Mar 9, 2017
    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?

  5. aldol16

    aldol16 2+ Year Member

    Nov 1, 2015
    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.
    ys2327 likes this.
  6. aldol16

    aldol16 2+ Year Member

    Nov 1, 2015
    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).

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