Amino Acids

Flashcards covering the structure and characteristics of the the 20 standard amino acids.

Glycine

Smallest side chain; only amino acid with no chiral carbon; most flexible amino acid in a protein chain.

Alanine

Small side chain, non-polar (aliphatic).

Isoleucine

Branched amino acid with a tertiary carbon atom in the side chain & this a.a. has more than one chiral C, non-polar (aliphatic).

Leucine

Branched amino acid with a tertiary carbon atom in the side chain, non-polar (aliphatic).

Valine

Branched amino acid with a tertiary carbon atom in the side chain, non-polar (aliphatic).

Methionine

Sulfur is non-polar, roughly the size of a CH2 group; sulfide/thioether functional group; non-polar (aliphatic).

Proline

Forms a ring with the amino acid N; least flexible amino acid in protein; non-polar, cyclic, aliphatic.

Cysteine

S-H bond (thiol group) has polarity; pKa ~8 for thiol H; S often makes disulfide bonds with other C side chains; polar, uncharged.

Tryptophan

Largest amino acid; mostly non-polar; fused rings are aromatic; non-polar and aromatic.

Phenylalanine

Has an aromatic ring group on the side chain; non-polar and aromatic.

Tyrosine

Aromatic group is non-polar & can make hydrophobic interactions; hydroxyl group H can make H-bonding interactions; H on the hydroxyl has a pKa of 10.1 & can be deprotonated; side chain is a phenol group; aromatic and polar, uncharged.

Glutamine

Amide group allows for H attached to N and carbonyl Oxy to make H-bonding interactions; more concentrated in blood and is considered a N carrier; polar, uncharged.

Serine

Side chain has an alcohol functional group; can be phosphorylated converting hydroxyl to a phosphate group (and a negative 2 charge at neutral pH); polar, uncharged.

Threonine

Side chain has an alcohol group, more than one chiral C and can be phosphorylated converting hydroxyl to a phosphate group (and a negative 2 charge at neutral pH); polar, uncharged.

Lysine

Side chain pKa is 10.5; If the N at the end of the side chain becomes acetylated, this amino acid becomes polar and uncharged; polar, charged, basic (positively charged).

Asparagine

Amide group allows for H attached to N and carbonyl Oxy to make H-bonding interactions; one C shorter than Q; polar, uncharged.

Arginine

Has a guanidine functional group and the side chain pKa is 12.5; Polar, charged, basic (positively charged).

Glutamate (glutamic acid)

Has a carboxylic acid or carboxylate functional group & the side chain pKa is 4.3; Polar, charged, acidic (negatively charged).

Aspartate (aspartic acid)

Has a carboxylic acid or carboxylate functional group; one C shorter than E & the side chain pKa is 3.7; Polar, charged, acidic (negatively charged).

Histidine

Side chain pKa is 6; Only one N in the side chain is protonated; side chain group is called an imidazole ring; Polar, aromatic, charged, basic (positively charged).