(polar uncharged amino acids)
(basic amino acids)
• np. aliphatic AA, np., not v. reactive
o glycine (Gly, G)
§ same substit., smallest
o alanine (Ala, A)
o beta-branch AA become more
hydrophob. & np.
§ valine (Val, V)
§ leucine (Leu, L)
§ Isoleucine (Ile, I)
• np. AA
o proline (Pro, P)
§ most sterically hindered AA
• b/c a-amino fxn & a-carbon
attached through ring sys.
§ only slightly hydrophobic
§ found at end of a-helices
o methionine (Met, M)
• np. aromatic AA, aromatic rings hydrophobic
o phenylalanine (Phe, F)
o Tyrosine (Tyr, Y)
§ –OH, polar
• can np. or polar
(acidic amino acids)
• polar AA (polar uncharged)
o serine (Ser, S)
o cysteine (Cys, C)
§ HS, v. reactive biochemically
• only AA that can form di-sulf.
bonds, to form cov. bond, takes 2
cysteines
§ easily alkylated
o threonine (Thr, T)
o asparagine (Asn, N)
§ ø prot. under physiological fxn
• b/c of resonance
o glutamine (Gln, Q)
§ ø prot. under physiological fxn
• b/c of resonance
• (+)ly charged polar AA (basic AA)
o histidine (His, H)
§ pKR close to physiological pH à pKr
often altered by local enviro.
o lysine (Lys, K)
o arginine (Arg, R)
• (-)ly charged polar AA (acidic AA)
o aspartic acid (Asp, D)
o glutamic acid (Glu, E)
• steric hindrance
o Val, Leu, Ile, Phe, Trp
• –OH only ionizable under v. basic cond., –OH
group v. reactive
o Ser, Thr, Tyr
• hydrophilic
o Asn, Gln, Cys, Asp, Glu
• only slightly hydrophilic
o Ser, Thr, Tyr
• ionizable
o Arg (12.5), Asp (3.9), Cys (8.3), Glu (4.2),
His (6.0), Lys (10.0), Tyr (10.1)
• ~2 a-carboxyl, ~ 10 a-amino