Large Molecules Problem Set
Problem 1: Recognition of the peptide bond
Tutorial to help answer the question
Which arrow points to a peptide bond?
The polypeptide chains of proteins are linear polymers of amino acids linked by peptide bonds. Each amino acid has an amino group (-NH2) and a carboxyl group (-COOH) that are used for peptide bond formation.
As shown in the diagram, the peptide bond forms between the carbon atom (C) of the carboxyl group and the nitrogen atom (N) of the amino group. The elements of water are removed as a by product of this reaction. Water (HOH) forms from the -OH of the carboxyl group of one amino acid and a hydrogen from the -NH2 group of the other amino acid.
| In this diagram, we visually separate the individual amino acids at the peptide
bonds. Note that the backbone of the peptide is formed from a repeating
pattern of the atoms N-C-C, corresponding respectively to the amino
nitrogen-alpha carbon-carbonyl carbon of the individual amino acids.
The groups shown as R1, R2, R3, etc represent the side chains of different
The Biology Project
Department of Biochemistry and Molecular Biophysics
The University of Arizona
Revised: October 2004
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