[27.2] (1/2) amino acids
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what is the general formula for an α-amino acid?
RCH(NH₂)COOH
what groups is an amino acid composed of?
• amine group (NH₂) • carboxyl group (COOH) • variable R group
what are α-amino acids?
when the two functional groups are bonded to the same carbon
what reactions can amino acids undergo?
• base reacts with acids • CA reacts with alkalis • CA reacts with alcohols (esterification)
what is formed when the amine group reacts with an acid?
ammonium salt + ion is formed
what is formed when the carboxylic acid group reacts with aqueous alkalis?
carboxylate salt + water
describe the esterification of amino acids with alcohols
• reactants = amino acid + alcohol + H⁺ • products = ester + water • acidic conditions protonate the basic group of the amine so it becomes N⁺H₃
what is a zwitterion?
a structure which has a full positive and full negative charge in its structure, but no overall charge as the positive and negative cancel each other out
how is a zwitterion formed in an amino acid?
basic NH₂ can accept a H+ from the COOH group to form an ion containing a + and - charge
what is the significance of amino acids as zwitterions?
explains why AAs show the properties of ionic substances eg. high melting point
what is the isoelectric point?
pH at which a zwitterion is formed
how is an AA zwitterion unique?
• each AA has its own unique isoelectric point • some R groups also contain basic or acidic groups
what happens if an AA is added to a solution with a pH lower / higher than its isoelectric point?
• pH lower = AA behaves like a base ang gains a proton (H⁺) • pH higher = AA behaves like an acid and loses a proton (H⁺)