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Amino Acid Configuration quiz #1 Flashcards

Amino Acid Configuration quiz #1
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  • Which amino acid is the only achiral amino acid, and why is it considered achiral?
    Glycine is the only achiral amino acid because its side chain is a hydrogen atom, making its alpha carbon attached to two identical groups.
  • What convention do biochemists use to denote the chirality of amino acids, and which form is predominantly found in proteins?
    Biochemists use Fischer's convention, denoting L and D forms, and proteins are almost exclusively made from L amino acids.
  • What is the relationship between the L/D and R/S configurations in amino acids, and which amino acid is the exception?
    Most L amino acids have an S configuration, except for L-cysteine, which has an R configuration due to its unique side chain priority.
  • How can you quickly identify an L amino acid in a standard Fischer projection?
    In a standard Fischer projection, an L amino acid has the carboxyl group on top, the R group on the bottom, and the amino group on the left.
  • Why does L-cysteine have an R configuration instead of S, unlike other L amino acids?
    L-cysteine has an R configuration because its sulfur-containing side chain gives it a higher priority than the carboxyl group when assigning priorities.
  • Describe a quick visual method to recognize an L amino acid in a three-dimensional representation.
    If the amino group is going down and on a wedge, or if the R group is going down and on a dash, it is an L amino acid.
  • What is the significance of the orientation of groups in a Fischer projection for determining L or D configuration?
    The orientation determines configuration: if the amino group is on the left (with carboxyl on top and R group on bottom), it is L; if on the right, it is D.
  • Are D amino acids ever found in nature, and if so, where?
    Yes, D amino acids are found in some bacterial cell walls, but are rare in proteins of higher organisms.
  • Why is it important to recognize different representations of L amino acids, and which representation is most commonly used for R group analysis?
    Recognizing different representations helps quickly identify L amino acids without full configuration analysis; the most common for R group analysis is the one with the R group going down and dashed.
  • Which amino acid is the only achiral amino acid, and why is it considered achiral?
    Glycine is the only achiral amino acid because its side chain is a hydrogen atom, making its alpha carbon attached to two identical groups.