Amino acids and chirality

Question 1

What is the general formula for an a-amino acid?

Answer 1

RCH(NH2)COOH

Question 2

what is the isoelectric point?

Answer 2

this is the pH at which an amino acid exists as a zwitterion.

Question 3

what causes the variation in isoelectric points?

Answer 3

different R groups on a-amino acids

Question 4

describe the properties of an amino acid at a pH that is lower than the isoelectric point

Answer 4

• more acidic
• amino acid behaves as a base and accepts a proton from the acid
• amino acid forms a positively charged ion

Question 5

describe the properties of an amino acid at a pH that is higher than the isoelectric point

Answer 5

• more alkaline
• amino acid behaves as an acid and donates a proton to the base
• amino acid forms a negatively charged ion

Question 6

describe the formation of a peptide linkage

Answer 6

CONDENSATION REACTION

- water is eliminated

Question 7

describe the acid hydrolysis of polypeptides and proteins

Answer 7

• hydrolysed used aq acid
• amino acids formed are positively charged because of the presence of H+ ions
• heated under reflux for 24 hours

Question 8

describe the alkaline hydrolysis of polypeptides and proteins

Answer 8

• alkali solution (aq sodium hydroxide)
• 100 degrees celsius
• polypeptide broken down into amino acids in the form of their sodium salts

Question 9

define “optical isomers”

Answer 9

non superimposable mirror images around an organic chiral centre (4 different groups attached to a carbon atom)

Question 10

what is a chiral centre

Answer 10

4 different groups attached to a carbon atom

Question 11

what are stereoisomers?

Answer 11

species with the same structural formula but with a different arrangement of atoms in space. Optical isomerism and E/Z isomerism are two examples of this.