Functions and Chemistry of Amino Acids

Defensins

Small proteins with antimicrobial properties.

D- or L- amino acid?

• L if the amino acid is pointing to the left

• D if the amino acid is pointing to the right

• this is an L amino acid

which way is rthe amino acid sequence read?

the sequence reads from the N-terminus → C-terminus

the N-terminus is that with a free amino group

the C-terminus is that with a free carboxylate group

proline

• does not fit in any category

• much less hydrophobic than aliphatic

• rotation around n-c alpha bond is restricted

Zwitterion

Molecule with both positive and negative charges.

Chiral centre

Carbon atom bonded to four different groups.

Stereoisomers

Molecules with the same formula but different arrangements.

Enantiomers

Stereoisomers that are mirror images.

Aliphatic amino acids

• Amino acids with non-aromatic hydrocarbon side chains

• glycine

• alanine

• valine

• leucine

• isoleucine

Hydrophobicity of the aliphatic amino acids

alanine, valine, leucine and isoleucine have increasing hydrophobicity

Branched chain amino acids in the aliphatics

• valine

• leucine

• isoleucine

most hydrophobic aliphatic and advantage

isoleucine

• protein folding

Aromatic amino acids

• phenylalanine

• tyrosine

• tryptophan

• histidine

which aromatic amino acids can make hydrogen bonds

histidine and tyrptophan

Hydroxyl amino acids

• tyrosine

• serine

• threonine

  • ALL POLAR

polarity in hydroxyl amino acids

serine and threonine are more polar than tyrosine

• form hydrohen bonds

• and phosphate esters - signalling

Sulfur containing amino acids

• cysteine

• methionine

Disulfide bonds

Covalent bonds formed between cysteine residues.

cysteine characteristics

• weak hydrogen bonds

• stronger amino acid than serine

• ionisable

• forms disulfide bonds

Acidic amino acids

• aspartate

• glutamate

acidic amino acids characteristics

• form salt bridges and polar interactions with water

• hydrogen bonds

• negative charge due to extra carboxyl group on side chain

amides of acidic amino acids

• asparagine

• glutamine

characteristics of amides of amino acids

• not ionisable

• highly polar

• strong hydrogen donor and acceptor

Basic amino acids

• lysine

• arginine

  have positively charged side chain

Guanidino group

Functional group in arginine contributing to basicity.

strongest basic amino acid

arginine

• due to guanidino group