Introduction to Structure and Properties of Biological Tissues

Abstract

Macromolecules and polymers are the principle building blocks of tissues. Without these large molecules, life as we know it would not be possible, because these moieties are responsible for the completion of most biological processes. Biological macromolecules are classified into four groups of large molecules: proteins, polysaccharides (sugar polymers), nucleic acids, and lipids. These classes are differentiated by their repeat units, the chemical structure that is repeated over and over again to make a large chain. The properties of long chains of repeat units linked together are dependent on the chemistry of the chain. The physical properties of long-chained molecules also depend on the rotational freedom around the backbone, as diagrammed in Figure 2.1. Regardless of the exact chemistry of a macromolecule–s backbone, the physical behavior is fixed. The modulus or resistance of a polymer to deformation is independent of the backbone chemistry, but the temperature at which a particular behavior is observed is dependent on the backbone chemistry. At some temperature, all polymers behave like a rubber band, stretching easily and reversibly. This temperature, at which a polymer behaves like a rubbery material, is the glass-transition temperature. The glass-transition temperature is affected by the chemistry of the repeat unit and by how it affects the backbone flexibility. The relationship between the chemistry of the backbone of a polymer and its rubberiness is more complex than just analysis of the backbone rotational freedom; this is discussed later in this chapter.