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Homework Help: Casein in water solution

  1. Nov 4, 2011 #1
    What happens when you put protein in water?

    I know that an amino acid in water vill dissolve into:
    [tex]^{+}H_3 N-CHR-COO^{-}[/tex]
    As protein is built up by over 50 amino acids, will the very same thing (as the formula above) happen to it?

    (My homework is to explain why Casein produces a residue when put into a water solution with pH≈4,6)
  2. jcsd
  3. Nov 4, 2011 #2


    User Avatar

    Staff: Mentor

    Protein is in a way similar to a single amino acid. You should be able to see it if you draw a simple protein, say GlyGlyGly.
  4. Nov 5, 2011 #3
    I think this is the answer to the question why Casein produces a residue when put into a water solution with pH≈4,6 (but I'm very uncertain)

    At that pH, this is what happens:

    [itex] H_2N-CHR-COOH \rightarrow ^{+}H_3N-CHR-COO^{-} [/itex] (Amino acid put into water solution)

    [itex] pH ≈ pI \Rightarrow [^{+}H_3N-CHR-COOH] = [H_2N-CHR-COO^{-}] [/itex]

    This leads us to the fact that there are no repulsive forces between the amino acids, thus the R-group of the amino acids of Casein are able to attract each other via van der Waals-bonds.
    When pH≠pI the protein can not come together, because of the repulsive forces.

    Correct, or incorrect?
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