CH1 | Amino Acids (PT2) Flashcards
Optical Properties
What is the defining characteristic of the alpha-carbon in most amino acids that leads to optical activity, and which common amino acid is the exception?
The alpha-carbon is usually attached to four different chemical groups, making it chiral and thus optically active (able to rotate plane-polarized light). Glycine is the exception, having two hydrogen atoms attached to its alpha-carbon, making it achiral and optically inactive.
What are stereoisomers, and how do enantiomers relate to optical activity?
Stereoisomers are molecules with the same chemical formula but different spatial arrangements. Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. They rotate plane-polarized light in opposite directions, leading to optical activity.
All human protein amino acids exist in what stereoisomeric form, and where are D-amino acids found?
All proteogenic amino acids in humans are L-stereoisomers. D-amino acids are rare, found only in some small peptides, bacterial cell walls, and certain peptide antibiotics.
Name some non-protein nitrogenous compounds derived from amino acids?
Heme, Histamine, Serotonin, Catecholamines, Melanine.
What are the three main groups that can affect the ionization state of an amino acid, making amino acids amphoteric?
The amino group (NH2), the carboxyl group (COOH), and the ionizable R group (in some amino acids, such as Lysine or Aspartate). This allows amino acids to act as weak acids and bases, thus they are considered amphoteric and act as buffers in solution.
What does “zwitterion” or “isoelectric point” (pI) mean regarding the overall charge and pH for a given amino acid?
Zwitterion refers to the dipolar form of an amino acid with a net charge of zero, having a negatively charged carboxyl group and a positively charged amino group. The isoelectric point (pI) is the pH at which an amino acid exists as a zwitterion (thus net charge = 0).
