Amino Acid Side Chains

Question 1

Aliphatic hydrophobic amino acids

Answer 1

Alanine -CH3
Valine -CH(CH3)2
Leucine -CH2CH(CH3)2
Isoleucine -CH(CH3)CH2CH3
Methionine -CH2CH2SCH3

Question 2

Aromatic amino acids

Answer 2

Phenylalanine -CH2-C6H5 (hydrophobic)
Tyrosine -CH2-C6H4-OH
Tryptophan -NH can form H-bonds but molecule mainly hydrophobic

Question 3

Uncharged polar hydrophilic amino acids

Answer 3

Asparagine -CH2C=ONH2
Glutamine -CH2CH2C=ONH2
*amide group is polar but does not ionise so less hydrophobic
Serine -CH2OH
Threonine -CHOHCH3
*OH is polar so forms H-bonds so is hydrophilic

Question 4

Ionised hydrophilic amino acids

Answer 4

Aspartic acid -CH2COOH
Glutamate -CH2CH2COOH
*Acidic COOH side chain - hydrophilic
Lysine -C4H8NH3+
Arginine -C3H6NHC=NH2+NH
*Strong basic side chains
Histidine -CH2-(cyclic C-NH=CH-NH-CH=)
*Weakly basic pKa=6 -side chains form H-bonds + salt bridge

Question 5

Amino acids with unusual properties

Answer 5

Cysteine -CH2SH
*Forms disulphuide bridges
Proline -NH2 imino group - hydrophobic
*Puts a kink into conformation of polypeptide chains