Amino Acids

Question 1

Alanine

Answer 1

Ala - A

• location: various locations
• hydrophobic
• aliphatic
• only a methyl group
• quite frequent (7.7%)

Question 2

Arginine

Answer 2

Arg - R

• location: on the surface of proteins
• hydrophilic
• basic (pKa 12.5)
• aliphatic
• planar guanidium group
• long, flexible amino acid

Question 3

Asparagine

Answer 3

Asn - N

• location: surface
• hydrophilic
• neutral, polar - carboxamide group​
• aliphatic
• sometimes glycosylated

Question 4

Aspartate

Answer 4

Asp - D

• location: surface
• hydrophilic
• acidic (pKa 3.5) - carboxylate group
• aliphatic

Question 5

Cysteine

Answer 5

Cys - C

• location: disulphides
• ionizable (pKa 8.5)
• aliphatic
• thiol group (SH)
• oxidation ⇒ cystine (joint cysteines)
• reduction ⇒ 2 cysteines
• rare (2.0%)

Question 6

Glutamate

Answer 6

Glu - E

• location: surface
• hydrophilic
• acidic (pKa 4.5) - carboxylate group
• aliphatic

Question 7

Glutamine

Answer 7

Gln - Q

• location: surface
• hydrophilic
• neutral, polar - carboxamide group​
• aliphatic

Question 8

Glycine

Answer 8

Gly - G

• location: in various locations and in loops
• hydrophobic
• aliphatic
• no R-group (not CHIRAL)
• quite common (7.4%)

Question 9

Histidine

Answer 9

His - H

• location: active sites
• hydrophilic
• basic (pKa 6.5) - imidazole group
• aromatic
• good for enzymatic activity (pKa close to 7)
• rare (2.3%)

Question 10

Isoleucine

Answer 10

Ile - I

• location: in the interiors
• hydrophobic
• aliphatic
• same mass as leucine

Question 11

Leucine

Answer 11

Leu - L

• location: in the interiors
• hydrophobic
• aliphatic
• most common amino acid (8.5%)

Question 12

Lysine

Answer 12

Lys - K

• location: surface
• hydrophilic
• basic (pKa 10.5)
• aliphatic
• can undergo acetylation

Question 13

Methionine

Answer 13

Met - M

• location: interior
• hydrophobic
• aliphatic
• contains sulphur (thioether)
• rare (2.4%)

Question 14

Phenylalanine

Answer 14

Phe - F

• location: interiors
• hydrophobic
• aromatic - phenyl group
• can rotate around its methyl group

Question 15

Proline

Answer 15

Pro - P

• location: surfaces and loops
• not aromatic (ring can pucker)
• pyrrolidine that circles back onto the peptide nitrogen (cyclic)

Question 16

Serine

Answer 16

Ser - S

• location: surface
• neutral, polar - hydroxyl group
• aliphatic
• sometimes phosphorylated/glycosylated

Question 17

Threonine

Answer 17

Thr - T

• location: surface
• hydrophilic
• polar, neutral - hydroxyl group
• sometimes glycosylated/phosphorylated
• has 2 chiral centres

Question 18

Tyrosine

Answer 18

Tyr - Y

• location: interior
• hydrophobic
• ionizable (pKa 10) - phenol group
• aromatic
• absorbs UV (280nm)

Question 19

Tryptophan

Answer 19

Trp - W

• location: interior
• mostly hydrophobic, but NH group has some hydrophilic property
• aromatic - indole group
• absorbs UV (280nm)
• fluoresces at different wavelengths
• most uncommon amino acid (1.4%)

Question 20

Valine

Answer 20

Val - V

• location: interior
• hydrophobic
• aliphatic

Question 21

What are the hydrophilic acidic amino acids?

They have carboxylate groups

Answer 21

• Asp (D)
• Glu (E)

Question 22

What are the hydrophilic basic amino acids?

Answer 22

• Lys (K)
• Arg (R)
• His (H)

Question 23

What are the hydrophilic, neutral, polar amino acids?

Answer 23

• Asn (N)
• Gln (Q)
• Ser (S)
• Thr (T)

Question 24

What are the hydrophobic aliphatic amino acids?

they have methyl groups

Answer 24

• Ala (A)
• Val (V)
• Leu (L)
• Ile (I)
• Met (M)

Question 25

What are the hydrophobic, aromatic amino acids?

Answer 25

• Phe (F)
• Tyr (Y)
• Trp (W)