Basics of AA's

Question 1

Alanine A (Ala)

Answer 1

Methyl (CH3)
Nonpolar
Hydrophobic
No charge
Ambivalent (in/outside of protein molecule)

Question 2

Arginine R (Arg)

Answer 2

3(CH2)-NH-C(2NH2) - one +NH2
Basic R group
Polar
Positively charged
Designed to bind phosphate anion.

Question 3

Asparagine N (Asn)

Answer 3

Neutral
Polar
Uncharged
Amide of aspartic acid.
Easily hydrolyzed to convert asparagine to aspartic acid.
High H-bond ability since amide group can accept and donate 2 H bonds.
Common site for carbohydrate attachment in glycoproteins.

Question 4

Aspartic Acid D (Asp)

Answer 4

Acidic
Polar
Charged
General acids in enzyme active centers.
Maintain solubility / ionic character of proteins.
An alanine w/ a beta-H replaced by carboxylic acid group.

Question 5

Cysteine C (Cys)

Answer 5

Sulfur containing
Polar
Uncharged
Weak H-bonding
Reactive
Can react w/ itself to form oxidized dimer via disulfide bond formation.
Play key stabilizing role in extracellular environment (intra - strongly reducing - can’t form disulfides)

Question 6

Glutamic Acid E (Glu)

Answer 6

Acidic
Polar
Charged
Acidic R group
Biosynthesis of Proline
One more methylene group than aspartic acid, creates inductive effect, higher pKa than aspartic acid.

Question 7

Glutamine Q (Gln)

Answer 7

Neutral
Polar
Uncharged
Amides of acidic AAs R group

Question 8

Glycine G (Gly)

Answer 8

H only
Achiral
Aliphatic R group
Nonpolar
Smallest
Ambivalent (in / outside protein)

Question 9

Histidine H (His)

Answer 9

Basic
Polar
Positively charged
Essential - positively charged imidazole FG:
unprotonated - nucleophilic,  general base.
protonated, general acid.
Common in enzyme catalyzed rxns.
Stabilizes folded protein structure.

Question 10

Isoleucine I (Ile)

Answer 10

CH(-CH3)-CH2-CH3
Aliphatic R group
Nonpolar
Essential - hydrocarbon side chains.
Nonreactive
Interchangeable w/ leucine / sometimes valine.
Roles in ligand binding to proteins.
Protein stability.
2 chiral centers.

Question 11

Leucine L (Leu)

Answer 11

Aliphatic R group
Nonpolar
Hydrophobic
1:3 AA's w/ branched hydrocarbon side chain
one more methylene group than valine

Question 12

Lysine K (Lys)

Answer 12

CH2-CH2-CH2-CH2-NH3+
Basic R group
Polar
(+) charge (primary amine)
highly reactive
(alanine w/ propylamine on beta C.)

Question 13

Methionine M (Met)

Answer 13

CH2-CH2-S-CH3
sulfur-containing
Nonpolar
Hydrophobic
Not highly nucleophilic
Contains thiol ether
Prone to oxidation

Question 14

Phenylalanine F (Phe)

Answer 14

CH2-benzene ring
Aromatic R group
Nonpolar
Hydrophobic
(alanine w/ phenyl on beta C)

Question 15

Proline P (Pro)

Answer 15

Cyclic
Nonpolar
Cis-Trans configuration
(plays important role in protein folding)

Question 16

Serine S (Ser)

Answer 16

Non-aromatic hydroxyl
Polar
Uncharged
Hydrophilic
(alanine w/ methyl H replaced w/ OH)

Question 17

Threonine T (Thr)

Answer 17

Non-aromatic hydroxyl
Polar
Uncharged
Hydrophilic
alpha and beta C are optically active.

Question 18

Tryptophan W (Trp)

Answer 18

Aromatic R group
Nonpolar
Largest AA
Indole N can H-bond donate

Question 19

Tyrosine Y (Tyr)

Answer 19

Aromatic group
Hydroxyl group
Nonpolar
(more soluble that phenylalanine)

Question 20

Valine V (Val)

Answer 20

CH(CH3)-CH3
Aliphatic R group
Nonpolar
Hydrophobic