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destroyer #291 bio

Discussion in 'DAT Discussions' started by 113zami, Jun 6, 2008.

  1. 113zami

    2+ Year Member

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    simple question, what does pKR(R is a subscript) stand for in that question, they never mention it in the explanation?
    thanks
     
  2. creative8401

    creative8401 Im Anush Hayastan
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    Hello! :) Amino acids have an N-terminus (amino end) and C-terminus (carboxyl group). One amino acid is different from another as a resulf of its variable group. This variable group is defined as R. So R means the pK value for the side chain. Since th amino acid has an amino group it too has a pK value. Glycine for instance does not because the R group is a hydrogen.
     
  3. Predentole

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    This question is actually really confusing. Can someone simplify the destroyer's explaination?
     
  4. creative8401

    creative8401 Im Anush Hayastan
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    Hi everyone. Sure thing, lets take a look at this problem.

    They say “sophisticated”, but I say all you need to know is one fact.

    pH > pKa: deprotonated

    In words, when the pH value is greater than the pKa, the corresponding amino group or carboxyl group will be deprotonated, and by this I mean the amino group will be NH2 and carboxyl group would be O-

    A) pH = 7
    pH < pKa (9.2 or 10.8); thus protonated
    They have “deprotonated” - =)

    B) pH > all of the pK values given, ok amino groups are NH2 and carboxyl groups are negative. Since we have two amino groups, if they were protonated, it would be like putting two positive ends of a magnet together, and they would repel. Thus, the destabilizing effect of the amino groups is removed.

    C) pH < pKa; all protonated, ok…so carboxyl exists as OH, and amino groups are all NH2, remember that magnet analogy above….

    D) pH < pKa; prot. and thus destabilize the ring

    So remember only: pH > pKa: deprotonated to solve their “sophisticated” problem. Hope this helps.
     

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