topic 3 - peptides Flashcards
what are peptides?
peptides are chains of amino acids
Amino acids are linked into sequence-defined polymers
This arranges the side chains, and their respective functionality, in space
Amino acid sequence
protein structure
protein function + drug interactions
what are peptide bonds?
peptide bonds are amide bonds
Amides are a product of a condensation reaction between amines and carboxylic acids. The other product is water, hence the name.
what is the structure of an amide bond?
The nitrogen lone pair is conjugated to the C=O double bond, creating a partial double-bond between N and C.
Due to orbital constraints, no free rotation about the C-N bond. The group is planar
Amide nitrogens are NOT nucleophilic.
amide bond stability
Amides are one of the less reactive functional groups
Amides are stable to weakly acidic and basic conditions
Hydrolysis only occurs in under ‘extreme conditions’
how do amides synthesise? (amide synthesis)
Amides are synthesised from activated analogues of carboxylic acids
Amines act as nucleophiles, acid derivatives as electrophiles
amide synthesis
Dicyclohexylcarbodiimide (DCC) is a more common activating agent because it allows one-pot synthesis
H2O has been transferred onto the DCC to give a urea side product
peptide synthesis?
no control of length or the sequence.
use protecting groups (PG) to prevent reaction at undesired site.
purification at each step makes the process extremely laborious.
what are writing sequences?
ALWAYS WRITE N-TERMINUS TO C-TERMINUS
Ser-Gly-Phe-Ala Ser-Gly-Phe-Ala
N terminus and C terminus
< 50 residues = peptide, oligopeptide (< ~10)
> 50 residues = polypeptide (unfolded), protein (folded)
how do you write sequences?
Y G G F L
Tyr-Gly-Gly-Phe-Leu
YGGFL
Y G G F L
AcTyr-Gly-Gly-Phe-LeuNH2
AcYGGFLNH2
Dipeptide = 2 amino acids; Tripeptide = 3 amino acids; Tetrapeptide = 4 amino acids, etc, etc
