Amino Acids

Question 1

Alanine (Ala)

Answer 1

• Aliphatic R group
• Hydrophobic
• Participates in hydrophobic interactions
• Smallest chiral AA

Question 2

Valine (Val)

Answer 2

• Aliphatic R group
• Highly hydrophobic
• Participates in hydrophobic interactions
• Branched carbon in sidechain

Question 3

Leucine (Leu)

Answer 3

• Aliphatic R group
• Highly hydrophobic
• Participates in hydrophobic interactions
• Branched

Question 4

Isoleucine (Ile)

Answer 4

• Aliphatic R group
• Highly hydrophobic
• Participates in hydrophobic interactions
• Branched
• Isomer of leucine

Question 5

Phenylalanine (Phe)

Answer 5

• Aromatic R group
• Highly hydrophobic
• Participates in hydrophobic interactions
• Phenyl group attached to alanine

Question 6

Tryptophan (Trp)

Answer 6

• Aromatic R group
• Heterocyclic
• Mostly hydrophobic
• Participates in hydrophobic interactions
• Forms H-bonds as a donor

Question 7

Methionine (Met)

Answer 7

• Aliphatic R group
• Hydrophobic
• Participates in hydrophobic interactions
• Sulfur containing side group
• Thioether

Question 8

Proline (Pro)

Answer 8

• Aliphatic side chain w. distinct cyclic structure
• Secondary amino group
• “imino” acid
• Hydrophobic
• Often found on protein surface even though it’s hydrophobic
• Has unique structural characteristics

Question 9

Glycine (Gly)

Answer 9

• Achiral
• Weakly polar
• Small side chain
• No significant hydrophobic aspect
• Very soluble in aqueous environment
• Very small
• Flexible (within polypeptides)
• More rotational freedom

Question 10

Serine (Ser)

Answer 10

• Polar, uncharged
• Contains hydroxyl group
• Forms H-bonds, typically as a H-donor
• Can be modified (e.g., phosphorylation)

Question 11

Threonine (Thr)

Answer 11

• Polar, uncharged
• Contains hydroxyl group
• Forms H-bonds, typically as a H-donor
• Can be modified (e.g., phosphorylation)

Question 12

Tyrosine (Tyr)

Answer 12

• pKa = 10.5
• Weakly polar, uncharged
• Aromatic R group (phenol)
• Can participate in hydrophobic interactions
• Contains hydroxyl groups
• Forms H-bonds, typically as a H-donor
• Can be phosphorylated

Question 13

Cysteine (Cys)

Answer 13

• pKa = 8.5
• Polar, uncharged
• Sulfur-containing side chain
• Can form H-bonds (as donor)
• Can form a thiolate anion (S-)
• Forms disulphide bonds with another Cys

Question 14

Asparagine (Asn)

Answer 14

• Polar, uncharged
• Amide-containing side chain
• Carboxamide functional group
• Forms H-bonds as a donor (NH2) and acceptor (C=O)

Question 15

Glutamine (Gln)

Answer 15

• Polar, uncharged
• Amide-containing side chain
• Carboxamide functional group
• Forms H-bonds as a donor (NH2) and acceptor (C=O)

Question 16

Histidine (His)

Answer 16

• pKa = 6.0
• Side chain can be acidic or basic at neutral pH
• Imidazole ring (aromatic)
• Polar, uncharged/charged
• Important in many enzyme catalyzed reactions
• Proton donor (acid)/acceptor (base)

Question 17

Aspartate (Asp)

Answer 17

• pKa = 4.0
• Negatively-charged at pH 7
• Second carboxyl group
• “Acidic” AA
• Very polar
• Forms H-bonds as acceptor
• pH 1 = aspartic acid

Question 18

Glutamate (Glu)

Answer 18

• pKa = 4.0
• Negatively-charged at pH 7
• Second carboxyl group
• “Acidic” AA
• Very polar
• Forms H-bonds as acceptor
• pH 1 = glutamic acid

Question 19

Lysine (Lys)

Answer 19

• pKa = 10.0
• Positively-charged at pH 7
• “Basic” AA
• Contains 2 primary amino groups
• Forms H-bonds as donor
• Very polar

Question 20

Arginine (Arg)

Answer 20

• pKa = 10.0
• Positively-charged at pH 7
• Guanido group
• “Basic” AA
• Contains 2 primary amino groups
• Forms H-bonds as donor (5 in side chain)
• Very polar