Polypeptide Nanowire and Protein Nanoparticle

Figure 12.6 illustrates the manner in which amino acids combine together in chains through the formation of a peptide bond. To form this bond, the hydroxy (—OH) of the carboxyl group of one amino acid combines with the hydrogen atom H of the amino group of the next amino acid, with the establishment of a C—N peptide bond accompanied by the release of water (H20), as displayed in the figure. The figure shows the formation of a tripeptide molecule, and a typical protein is composed of one or more very long polypeptide molecules. Small peptides are called oligopeptides, and amino acids incorporated into polypeptide chains are often referred to as amino acid residues to distinguish them from free or unbound amino acids. The protein haemoglobin, for example, contains four polypeptides, each with about 300 amino acid residues.

The stretched-out polypeptide chain, of the type shown at the top of Fig. 12.7, is called the primary structure. To become more compact locally, the chains either coil up in a what is called an alpha helix (a helix), or they combine in sheets called beta

Table 12.1. Typical sizes of various biological substances in the nanometer range




Size d (nm)

Amino acids

Glycine (smallest amino acid)

0 0

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