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where the molecular weight Afw is in daltons, and the volume V is in cubic nanometers.

Table 12.1 lists the molecular weights Mw and various length parameters d for a number of biological nanoparticles, Fig. 12.3 provides estimated molecular weights and dimensions of four proteins, and Table 12.2 lists sizes for biological structures and quantities that are larger than nanoparticles, in the micrometer region. All the amino acids have the common structure sketched in Fig. 12.4, with the acid or carboxyl group —COOH at one end, and an adjacent carbon atom that is bonded to a hydrogen atom, an amino group NH2, and a group R that characterizes the particular amino acid. Figure 12.S presents the structures of six of the amino acids, including the smallest acid, glycine, for which the R group is simply a hydrogen atom H, and the largest tryptophan in which R is a conjugated double-ring system. The structures of file nucleotide building blocks of DNA and RNA are presented in Section 12.3.1.

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