This section covers the peptide-linked backbone and variable side chains of polypeptides.
Polypeptide chains
A polypeptide is a long chain of amino-acid residues connected by peptide links. The chain has a repeating backbone, while the R groups attached to successive residues can differ.
Backbone and side chains
The peptide links form part of the common backbone.
The R groups extend from this backbone and distinguish the individual amino-acid residues.
A protein can contain a very large number of amino-acid residues, allowing long and complex chains to form.
Exam Tip: In a polypeptide diagram, trace the repeating backbone first and distinguish it from the R groups. The peptide linkage itself is the –C(=O)–NH– part of that backbone.
02•Proteins
Primary structure
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The amino-acid sequence
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