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Drawing a Peptide quiz

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  • What is the first step in drawing a peptide?
    The first step is to draw the peptide backbone and identify the alpha carbons.
  • What atoms make up the repeated backbone structure of a peptide?
    The backbone consists of repeated sets of nitrogen, carbon, and carbon (NCC) for each amino acid residue.
  • Which carbon in the NCC set is the alpha carbon?
    The middle carbon in the NCC set is the alpha carbon.
  • What group is attached to the alpha carbon in an amino acid?
    The R group is attached to the alpha carbon.
  • What is present at the N-terminal end of a peptide?
    The N-terminal end has a free and ionizable amino group (NH3+).
  • What is present at the C-terminal end of a peptide?
    The C-terminal end has a free carboxyl group, often drawn as a carboxylate anion with a negative charge.
  • Do internal amino acid residues in a peptide have free amino or carboxyl groups?
    No, only the terminal residues have free amino or carboxyl groups; internal residues lack both.
  • What is the second step in drawing a peptide?
    The second step is to add carbonyl groups to the backbone and consider amino acid chirality.
  • How is chirality depicted for L-amino acids in peptide drawings?
    If the R group is pointing up, it is drawn on a wedge; if pointing down, it is drawn on a dash.
  • Which form of amino acids is used in biological peptides?
    Biological peptides almost exclusively use L-amino acids.
  • What is the third step in drawing a peptide?
    The third step is to add hydrogen atoms to the nitrogen atoms and draw the R groups for each amino acid residue.
  • Should hydrogens on carbon atoms be drawn in peptide structures?
    No, hydrogens on carbon atoms can be assumed and do not need to be drawn.
  • What is the R group for alanine?
    Alanine's R group is a methyl group (CH3).
  • How is the R group for valine drawn?
    Valine's R group is a V-shaped structure with two methyl groups branching off a central carbon.
  • How does leucine's R group differ from valine's?
    Leucine's R group is an extended version of valine's, with an extra CH2 group before the V-shaped branching.