amino acids

Basic structure of amino acid

A-amino group, a-carboxylic acid, R group (side chain), central carbon attached to a hydrogen

Zwitterion

Forms when a molecule with both an acidic and a basic group undergoes an internal proton transfer, resulting in a molecule with both a positive and negative charge

Zwitterion high pH

Negatively charged

Zwitterion low pH

Positively charged

L- and D-amino acids difference

Configuration around chiral center

L-form

Amino group on left

D-form

Amino group of right

Essential amino acids that cannot be synthesised by the body and must be obtained through the diet

histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine

Direction of peptide sequences

From N-terminus to C-terminus

Peptide special bond

Partial double-bond character and planarity

Achiral amino acid

Glycine

Second chiral centre in side chain

Threonine and isoleucine

Peptide bonds

Amino acids can join together to form polymers - the join between them are peptide bonds

Peptide bond reaction

Requires the removal of one molecule of water = condensation reaction

Amino acid residues

Peptides and proteins are polymers of amino acid residues

Where are peptide bonds normally formed?

Ribosomes

N-terminus

The end with a free amino group (-NH2) - marks the start of sequence

C-terminus

The end with a free carboxylate group (-COOH) - makes the end of sequence

Lys-Phe

Consists of a lysine amino acid connected to a phenylalanine amino acid in a peptide bond - dipeptide formed from L-lysine and L-phenylalanine residues

Phe-Lys

Consists of a phenylalanine amino acid connected to lysine amino acid in a peptide bonds - dipeptide formed through L-phenylalanine and L-lysine residues

Functions of peptides

Signalling - hormones, growth factors, neurotransmitters

Antimicrobials (AMPs)

Research - generating antibodies, studying small parts of proteins

Important in the clinic - cancer therapy, obesity / diabetes