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Isoelectric Point quiz #1

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  • What is the isoelectric point (pI) of an amino acid, and why is it important in biochemical techniques such as electrophoresis?
    The isoelectric point (pI) of an amino acid is the specific pH at which the molecule has no net charge, meaning its positive and negative charges are balanced. At this pH, the amino acid does not migrate in an electric field, making pI crucial for techniques like electrophoresis, which separates molecules based on their charge.
  • How do you calculate the isoelectric point (pI) of an amino acid with a non-ionizable R group?
    To calculate the isoelectric point (pI) of an amino acid with a non-ionizable R group, take the average of its two pKa values (usually the pKa of the carboxyl group and the pKa of the amino group): pI = (pKa1 + pKa2) / 2.
  • What is the isoelectric point (pI) of an amino acid?
    The isoelectric point (pI) is the specific pH at which an amino acid has no net charge, with its positive and negative charges balanced.
  • Why is the isoelectric point (pI) important in biochemical techniques like electrophoresis?
    At the pI, a molecule does not migrate in an electric field, making it crucial for separating molecules based on charge in techniques like electrophoresis.
  • How do you calculate the isoelectric point (pI) for an amino acid with a non-ionizable R group?
    You calculate the pI by averaging the two pKa values of the amino acid: pI = (pKa1 + pKa2) / 2.
  • Which two pKa values are used to calculate the pI of an amino acid?
    The two pKa values associated with the ionizations that involve the neutral species are used to calculate the pI.
  • What happens to an amino acid at a pH equal to its isoelectric point?
    At a pH equal to its pI, the amino acid has no net charge and does not migrate in an electric field.
  • How does the acidity or basicity of an amino acid affect its isoelectric point?
    More acidic amino acids have lower pI values, while more basic amino acids have higher pI values.
  • Why is it important to only average two pKa values when calculating the pI, even if more are given?
    Only the two pKa values that bracket the neutral species are relevant for calculating the pI, regardless of how many pKa values are provided.
  • What is the formula for calculating the isoelectric point of valine, and what is its pI if pKa1 is 2.32 and pKa2 is 9.62?
    The formula is pI = (pKa1 + pKa2) / 2; for valine, pI = (2.32 + 9.62) / 2 = 5.97.