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Approximating Protein Mass quiz

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  • Which two amino acids have the same mass due to being isomers?
    Leucine and isoleucine have the same mass because they are isomers of each other.
  • What is the average molecular weight of the 20 free alpha amino acids?
    The average molecular weight of the 20 free alpha amino acids is 128 grams per mole.
  • What is lost during the formation of a peptide bond between amino acids?
    A water molecule (H2O) is lost during peptide bond formation.
  • How much does a water molecule weigh in grams per mole?
    A water molecule weighs 18 grams per mole.
  • What is the average molecular weight of an amino acid residue in a protein?
    The average molecular weight of an amino acid residue is 110 grams per mole.
  • How do you calculate the average molecular weight of an amino acid residue?
    Subtract the mass of a water molecule (18 g/mol) from the average mass of a free amino acid (128 g/mol) to get 110 g/mol.
  • What formula is used to approximate the mass of a protein?
    Multiply the total number of amino acid residues by 110 grams per mole.
  • Why is calculating the exact mass of a protein often cumbersome?
    Because proteins can contain hundreds or thousands of amino acids, each with a unique mass.
  • What does the term 'free' mean when referring to amino acids?
    'Free' means the amino acids are not linked by peptide bonds and are independent.
  • What is the approximate molecular weight of a protein with 200 amino acids?
    The approximate molecular weight is 22,000 grams per mole.
  • What type of reaction forms peptide bonds between amino acids?
    A dehydration synthesis reaction forms peptide bonds.
  • What abbreviations can be used for molecular weight?
    Molecular weight can be abbreviated as MW or Mr.
  • Why do we use an average residue mass instead of exact amino acid masses for proteins?
    Using an average residue mass simplifies calculations for large proteins with many amino acids.
  • How does the loss of water during peptide bond formation affect protein mass calculations?
    It reduces the average mass of each amino acid residue by 18 grams per mole.
  • If a protein has 500 amino acids, what is its approximate molecular weight?
    Its approximate molecular weight is 500 × 110 = 55,000 grams per mole.