Chapter 27: Amino Acids, Peptides and Proteins
Terminology and Conventions for Peptides and Proteins
Amines, -
NH
2
can react with carboxylic acids,
RCO
2
H
to form amides,
RCONH
2
(
review
?)
Proteins
are polymers of amino acids, linked by amide bonds
i.e.
proteins are just polyamides.
Peptides
are "short" proteins.
The amide bonds in peptides and proteins are also known as
peptide bonds
.
A
dipeptide
has two amino acid units,
e.g.
Ala-Gly (AG), a
tripeptide
three amino acid units
e.g.
Val-Leu-Ala (VLA), and so on...
The precise order of the amino acids in the peptide is the
amino acid sequence
.
Peptides are named according to their amino acid sequence.
By convention, the name is written so that the higher priority
carboxyl group
is to the
right
and the
amino
end to the
left
.
Note this "agrees" with the ideas of nomenclature where the higher priority group is used at the "right hand end" of the name
e.g.
2-aminoethanoic acid, H
2
NCH
2
CO
2
H
The carboxyl group end is referred to as the
C terminus
.
The amino group end is referred to as the
N terminus
.
The order of the naming is important as the two structures are not the same but are
constitutional isomers
.
QUESTIONS
Can you think of an example of a simple non-protein polyamide ?
ANSWER
Is the reaction of an amine with a carboxylic acid a good way of making amides ?
ANSWER
©
Dr. Ian Hunt
, Department of Chemistry
