Large Molecules Problem Set

Large Molecules Problem Set

Problem 1: Recognition of the peptide bond

Tutorial to help answer the question

Which arrow points to a peptide bond?

equation with 5 arrows pointing to different bonds

Tutorial

Amino acids

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.

Structural formula for an amino acid. Amino group and Carboxyl group identified

Peptide bonds

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.

Polypeptide chains

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 amino acids.

Diagram illustrating the above description

The Biology Project
Department of Biochemistry and Molecular Biophysics
The University of Arizona
Revised: October 2004
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