BSCI 330 Exam 1 - Amino Acid Side Chains

Leucine

Leu, L, nonpolar

Isoleucine

Ile, I, nonpolar

Tryptophan

Trp, W, nonpolar

Threonine

Thr, T, polar

Cysteine

Cys, C, polar

20

- naturally occurring amino acids
- universal (all organisms use it)

9

nonpolar side chains

glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, proline

6

polar side chains

serine, threonine, cysteine, tyrosine, asparagine, glutamine

5

- readily ionize at 7 pH (neutral)
- can do acid base chemistry

aspartate + glutamate (acidic), and histidine, lysine, arginine (basic)

2

- acidic electrically charged side chain
- completely ionized

aspartate, glutamate

3

- basic electrically charged side chain

lysine, arginine, histidine

7 pH

- neutral
- cellular pH

Glycine

Gly, G, nonpolar

Alanine

Ala, A, nonpolar

Valine

Val, V, nonpolar

Methionine

Met, M, nonpolar

Phenylalanine

Phe, F, nonpolar

Proline

Pro, P, nonpolar

Serine

Ser, S, polar

Tyrosine

Tyr, Y, polar

Asparagine

Asn, N, polar

Glutamine

Gln, Q, polar

Aspartate

- Asp, D, acidic, negative
- completely ionized (usually)

Glutamate

- Glu, E, acidic, negative
- completely ionized (usually)

Lysine

- Lys, K, basic, positive
- deprotonated
- 10-12 pka

Arginine

- Arg, R, basic, positive
- deprotonated
- 10-12 pka

ionized

- deprotonated
- environment pH is above pka
- negative charge

deionized

- protonated
- environment pH is below pka
- positive charged

Histidine

- His, H, basic, positive

- 6.5 pka, close to cellular pH

- 50% charged, 50% uncharged

- right in the middle (central amino acid)

pka important

- solution > 6.5 pka = uncharged

- solution < 6.5 pka = charged

- Very amenable to do acid base chemistry under cellular conditions, as it is just about 50% ionized at all times here

- do proton transport easily

> can deprotonate a substrate

> can protonate a substrate

pka

- pH at which a molecule is 50% ionized and 50% deionized

- more pH = more ionized