Amino Acids And Polypeptides

Question 1

Classification of optical isomers - R+S

Answer 1

Cahn-Inlog-Prelog rule
Identify chiral centre
Assign priority based on atomic number, 1=⬆️atomic no. 4=⬇️atomic no.
Position it so the lowest priority group pointing downwards
If priority is clockwise R
Anticlockwise S

Question 2

Peptide bond

Answer 2

Shorter than a normal bond

Partial double bond as it resonates between 2 states

Question 3

Secondry peptide structure

Answer 3

• ve PHI + PSI angles = alpha-helix

- ve PHI +ve PSI angles = beta-strand

Question 4

Classification of optical isomers - D+L

Answer 4

CORN rule
L = clockwise
D = anti-clockwise