Introduction to Nanotechnology

12
BIOLOGICAL MATERIALS
12.1. INTRODUCTION
It is customary to define nanoparticles or nanostructures as entities in the range of
sizes from 1 to 100 nm, so many biological materials are classified as nanoparticles.
Bacteria, which range in size between 1 and 10pm, are in the mesoscopic range,
while viruses with dimensions from 10 to 200nm are at the upper part of the
nanoparticle range. Proteins, which ordinarily come in sizes between 4 and 50 nm,
are in the low nanometer range. The building blocks of proteins are 20 amino acids,
each about 0.6nm in size, which is slightly below the official lower limit of a
nanoparticle. More than 100 amino acids occur naturally, but only 20 are involved in
protein synthesis. To construct a protein, combinations of these latter amino acids
are tied together one after the other by strong peptide chemical bonds and form long
chains called polypeptides containing hundreds, and in some cases thousands, of
amino acids; hence they correspond to nanowires. The polypeptide nanowires
undergo twistings and turnings to compact themselves into a relatively small
volume corresponding to a polypeptide nanoparticle with a diameter that is typically
in the range of 4-50 nm. Thus a protein is a nanoparticle consisting of a compacted
polypeptide nanowire. The genetic material desoxyribonucleic acid (DNA) also has
the structure of a compacted nanowire. Its building blocks are four nucleotide
molecules that bind together in a long double-helix nanowire to form chromosomes,
which in humans contain about 140 x lo6 nucleotides in sequence. Thus the DNA
Introduction to Nanotechnology, by Charles P. Poole Jr. and Frank J. Owens.
ISBN 0-471-07935-9. Copyright 0 2003 John Wiley & Sons, Inc.
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