Peptides Flashcards
(15 cards)
What are peptides?
Chains of amino acids
Amino acids are linked into sequence-defined polymers.
What is a chain of three amino acids called?
Tripeptide
When writing amino acid sequences in peptides, what order is it written in?
Always written from N-terminus to C-terminus.
What bonds are used in peptides?
Amide bonds
How are amide bonds formed?
Amide bonds are formed as a product of a condensation reaction between amines and carboxylic acids. The other product is water.
What’s 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.
Difference between amines and amides?
Amines are basic. Amine nitrogen’s are nucleophilic.
Amides are not basic and their nitrogen’s are not nucleophilic.
Amide bond stability
Amides are one of the less reactive functional groups.
Amides are stable to weakly acidic and basic conditions (contrast with esters).
Hydrolysis only occurs in under ‘extreme conditions’.
Amide synthesis
Amides are synthesised from activated analogues of carboxylic acids
Amines act as nucleophiles during the process, acid derivatives act as electrophiles.
Behaviour of amines
Why is Dicyclohexylcarbodiimide (DCC) used in amide synthesis?
As a common activating agent, allowing one-pot synthesis.
(H2O has been transferred onto the DCC to give a urea side product)
Carbodiimides
Carbodiimides are routinely used for amide/peptide synthesis.
Peptide synthesis
If just two amino acids were added together the product would be a random polymer - a polypeptide.
;there would be no control in the length or sequence.
Protecting groups in peptides synthesis
Using a protecting group (PG) prevents reactions from happening in undesired sites.
What are short peptides often used in?
Biologically signalling
