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Biopolymers are polymers produced by living organisms; in other words, they are polymeric biomolecules. Since they are polymers, biopolymers contain monomeric units that are covalently bonded to form larger structures. There are three main classes of biopolymers, classified according to the monomeric units used and the structure of the biopolymer formed: polynucleotides (RNA and DNA), which are long polymers composed of 13 or more nucleotide monomers; polypeptides, which are short polymers of amino acids; and polysaccharides, which are often linear bonded polymeric carbohydrate structures. 〔 Mohanty, A.K., et al., Natural Fibers, Biopolymers, and Biocomposites (CRC Press, 2005) 〕 〔 Chandra, R., and Rustgi, R., "Biodegradable Polymers", Progress in Polymer Science, Vol. 23, p. 1273 (1998) 〕 〔 Meyers, M.A., et al., "Biological Materials: Structure & Mechanical Properties", Progress in Materials Science, Vol. 53, p. 1 (2008) 〕 〔 Kumar, A., et al., "Smart Polymers: Physical Forms & Bioengineering Applications", Progress in Polymer Science, Vol. 32, p.1205 (2007) 〕 Cellulose is the most common organic compound and biopolymer on Earth. About 33 percent of all plant matter is cellulose. The cellulose content of cotton is 90 percent, while wood's is 50 percent. 〔 Klemm, D., Heublein, B., Fink, H., and Bohn, A., "Cellulose: Fascinating Biopolymer / Sustainable Raw Material", Ang. Chemie (Intl. Edn.) Vol. 44, p. 3358 (2004) 〕 == Biopolymers vs synthetic polymers == A major defining difference between biopolymers and other polymers can be found in their structures. All polymers are made of repetitive units called monomers. Biopolymers often have a well-defined structure, though this is not a defining characteristic (example: lignocellulose): The exact chemical composition and the sequence in which these units are arranged is called the primary structure, in the case of proteins. Many biopolymers spontaneously fold into characteristic compact shapes (see also "protein folding" as well as secondary structure and tertiary structure), which determine their biological functions and depend in a complicated way on their primary structures. Structural biology is the study of the structural properties of the biopolymers. In contrast, most synthetic polymers have much simpler and more random (or stochastic) structures. This fact leads to a molecular mass distribution that is missing in biopolymers. In fact, as their synthesis is controlled by a template-directed process in most ''in vivo'' systems, all biopolymers of a type (say one specific protein) are all alike: they all contain the similar sequences and numbers of monomers and thus all have the same mass. This phenomenon is called monodispersity in contrast to the polydispersity encountered in synthetic polymers. As a result, biopolymers have a polydispersity index of 1. 〔 Stupp, S.I and Braun, P.V., "Role of Proteins in Microstructural Control: Biomaterials, Ceramics & Semiconductors", Science, Vol. 277, p. 1242 (1997) 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「biopolymer」の詳細全文を読む スポンサード リンク
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