Amino Acids (lecture)

Non-polar AA

Gly, G
Ala, A
Val, V
Leu, L
Ile, I
Met, M
Pro, P
Phe, F
Trp, W

Polar Uncharged AA

Ser, S
Thr, T
Asn, A
Gln, Q
Tyr, Y
Cyc, C
His, H *

Polar + AA

anionic

Arg, R
Lys, K
His, H *

Polar - AA

Glu, E
Asp, D

pKa of AA

a - COOH 2.2
Aspartate 3.9
Glutamate 4.2
Histidine 6.0
Cysteine 8.3
a - NH3+ 9.5
Tyrosine 10.1
Lysine 10.5
Arginine 12.5
Serine 13.6
Threonine 13.6

Sterochemistry

conformation -rotation
configuration -breaking/forming

Isomers

same formula different arrangement
stereoisomer -same formula, different faces (up vs down)

Chirality

non-superimposable mirror images
-enantiomers D or L
AA are mostly L

Zwitterion

hybrid ion
-no net charge

Titration of glycine

pKa 1 = 2.4 (COOH)
pI = 6
pKa 2 = 9.6 (NH3+)

Isoelectric point

pI = pKa 1 + pKa/2

Calculating pH

1. determine form (A >6, B <6)
2. MV = mols of glycine (2 protons per mol)
3. MV = mols of added (NaOH)
4. 2g mols - n mols = leftover for B
5. pH = form pKa + log[base] (2g mol - n mol)/[acid] (n mol - g mol)

Titration of AA

Glycine 2.4, 9.6 A-B-C
Aspartate 1.9, 3.7, 9.6 A-B-C-D
Histidine 1.8, 6.0, 9.1 A-B-C-D
Lysine 2.2, 9.0, 10.5 A-B-C-D