AMINO ACIDS

GLY

GLYCINE, G

ALA

ALANINE, A

VAL

VALINE, V

LEU

LEUCINE, L

ILE

ISOLEUCINE, I

MET

METHIONINE, M

PRO

PROLINE, P

PHE

PHENYLALANINE, F

TRP

TRYPTOPHAN, W

SER

SERINE,S

THR

THERONINE, T

ASN

ASPARAGINE, N

GLN

GLUTAMINE, Q

TYR

TYROSINE, Y

CYS

CYSTEININE, C

LYS

LYSINE, K

ARG

ARGININE, R

HIS

HISTIDINE, H

ASP

ASPARTIC ACID, D

GLU

GLUTAMIC ACID, E

PKA FOR TYR

10.46 (phenol)

PKA FOR CYS

8.37 (sulfhydryl)

PKA FOR LYS

10.54 (ε-NH+ 3 )

PKA FOR ARG

12.48 (guanidino)

PKA FOR HIS

6.04 (imidazole)

PKA FOR ASP

3.90 (β-COOH)

PKA FOR GLU

4.07 Glu (γ-COOH)

pH decreases

When pH decreases (becomes more acidic):

• There are more H⁺ ions in solution.

• Amino acids become more protonated (they gain H⁺).

• Common changes:

  • Amino group (–NH₂) → –NH₃⁺

  • Carboxyl group (–COO⁻) → –COOH

• Side chains with acidic/basic groups also pick up protons.

Overall effect:

Amino acids carry more positive charge in low pH.

pH increases

When pH increases (becomes more basic):

• There are fewer H⁺ ions in solution.

• Amino acids become deprotonated (they lose H⁺).

• Common changes:

  • –NH₃⁺ → –NH₂

  • –COOH → –COO⁻

• Basic and acidic side chains lose protons depending on their pKa.

Overall effect:

Amino acids carry more negative charge in high pH.