[27.2] (1/2) amino acids

Question 1

what is the general formula for an α-amino acid?

Answer 1

RCH(NH₂)COOH

Question 2

what groups is an amino acid composed of?

Answer 2

• amine group (NH₂)
• carboxyl group (COOH)
• variable R group

Question 3

what are α-amino acids?

Answer 3

when the two functional groups are bonded to the same carbon

Question 4

what reactions can amino acids undergo?

Answer 4

• base reacts with acids
• CA reacts with alkalis
• CA reacts with alcohols (esterification)

Question 5

what is formed when the amine group reacts with an acid?

Answer 5

ammonium salt + ion is formed

Question 6

what is formed when the carboxylic acid group reacts with aqueous alkalis?

Answer 6

carboxylate salt + water

Question 7

describe the esterification of amino acids with alcohols

Answer 7

• reactants = amino acid + alcohol + H⁺
• products = ester + water
• acidic conditions protonate the basic group of the amine so it becomes N⁺H₃

Question 8

what is a zwitterion?

Answer 8

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

Question 9

how is a zwitterion formed in an amino acid?

Answer 9

basic NH₂ can accept a H+ from the COOH group to form an ion containing a + and - charge

Question 10

what is the significance of amino acids as zwitterions?

Answer 10

explains why AAs show the properties of ionic substances eg. high melting point

Question 11

what is the isoelectric point?

Answer 11

pH at which a zwitterion is formed

Question 12

how is an AA zwitterion unique?

Answer 12

• each AA has its own unique isoelectric point
• some R groups also contain basic or acidic groups

Question 13

what happens if an AA is added to a solution with a pH lower / higher than its isoelectric point?

Answer 13

• pH lower = AA behaves like a base ang gains a proton (H⁺)
• pH higher = AA behaves like an acid and loses a proton (H⁺)