[ M2 BIOCHEM ] Amino Acid Structure ; AA Ionization

Amino acids

Amino acids

Amino containing carboxylic acids

Alpha amino acids

Have only alpha/chiral carbon for both functional groups

L-isomer (NH2 at left)

Most organisms and humans have the ___ isomer of animo acids

Amphoteric

Since COOH is acidic and NH2 is basic, all amino acids are ___

Glycine, Gly, G

NP, -H

Glycine

The only non-chiral amino acid

Alanine, Ala, A

NP, methyl group (-CH3)

Valine, Val, V

NP, isopropyl (3)

Leucine, Leu, L

NP, isobutyl (4)

Branched chain AA

Isoleucine, Ile, I

NP, secbutyl (4)

Branched chain AA

Methionine, Met, M

NP, thioether

Proline, Pro, P

NP, 2° amino group

Proline

Imino acid , 2ndary amine

Phenylalanine, Phe, F

NP, phenyl

Aromatic AA

Tryptophan, Trp, W

NP, benzene & indole

Aromatic AA

Serine, Ser, S

P, 1° alcohol (C-OH)

Threonine, Thr, T

P, 2° alcohol (CC-OH)

Asparginine, Asn, N

P, beta amide (CO=CNH2)

Glutamine, Gln, Q

P, gamma amide (CCO=CNH2)

Tyrosine, Tyr, Y

P, phenolic hydroxyl

Cysteine, Cys, C

P, thiol / sulfhydryl

Lysine, Lys, K

P, epsilon amino

Basic

Arginine, Arg, R

P, guanidino group

Basic

Histidine, His, H

P, imidazole ring

Basic

Aspartic acid, Asp, D

P, beta carbonyl

Acidic

Glutamic acid, Glu, E

P, gamma carbonyl

Acidic

HRK - His, Arg, Lys

Basic amino acids

DE - Asp, Glu

Acidic amino acids

TPT - Try, Phe, Tyr

Aromatic amino acids

CM - Cys, Met

Sulfur containing amino acids

VIL - Val, Ile, Leu

Branched chain amino acids

LL - Leu, Lys

Amino acids that are only ketogenic (lead to ketone bodies)

PITTT - Phe, Ile, Try, Tyr, Thr

Amino acids that are both glucogenic and ketogenic

VMHR - Val, Met, His, Arg

Amino acids that are only glucogenic (lead to glucose)

pKa

In amino acids, ___ is constant, but pH can change

Zwitterion

Species with 0 net charge (NH3+ and COO- cancel each other out)

Neutral (COOH)

If pH < pKa (Pro), acidic group (COOH-) becomes ___

Ionized to positive (NH3+)

If pH < pKa (Pro), basic group (NH2) becomes ___

Ionized to negative (COO-)

If pH > pKa (Depro), acidic group (COOH) becomes ___

Neutral (NH2)

If pH > pKa (Depro), basic group (NH2) becomes ___

Deprotonation

pH > pKa; lowering of charge due to loss of H+

Protonation

pH > pKa

pH where all species are zwitterionic, have charge of 0

Isoelectric pH (iPH)

Average of 2 pKa’s around zwitterion

How to calculate isoelectric pH given 2 pKa values

Average of 2 pKa’s around zwitterion (form with one + and one -); ignore other pKa’s

How to calculate isoelectric pH given 3 pKa values

Cys, Tyr

Slightly acidic amio acids