Structure of Biologies

Just as we began our description of polymer structure with an organic chemistry review, let us begin our introduction to biological materials with some simple biochemistry. 

1 Amino Acids and Proteins. Proteins are the molecules that perform the functions of life. They can be enzymes that catalyze biological reactions, or they can be the receptor site on a membrane that binds a specific substance. Proteins are important parts of both bones—the so-called hard biologies—and the soft biologies such as muscle and skin. Any discussion of the structure of living organisms must begin with the structure of proteins. 

2 DNA and RNA. Like proteins, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are polymers, but instead of amino acids as repeat units, they are 

The nucleic acid polymer is formed when the nucleotides attach to one another through phosphodiester bonds, which connect the 3 -OH group of one nucleotide to the 5 -OH group of another nucleotide through the phosphate group. The order of the nucleotides in the chain is the primary structure of the DNA or RNA molecule, and it can be represented in short-hand notation with only the base pair designation 

As with proteins, the nucleic acid polymers can denature, and they have secondary structure. In DNA, two nucleic acid polymer chains are twisted together with their bases facing inward to form a double helix. In doing so, the bases shield their hydrophobic components from the solvent, and they form hydrogen bonds in one of only two specific patterns, called base pairs. Adenine hydrogen bonds only with thymine (or uracil in RNA), and guanine pairs only with cytosine. Essentially every base is part of a base pair in DNA, but only some of the bases in RNA are paired. The double-helix structure 

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The double bonds found in fatty acids are nearly always in the cis configuration. As shown in Figure 8.1, this causes a bend or kink in the fatty acid chain. This bend has very important consequences for the structure of biological membranes. Saturated fatty acid chains can pack closely together to form ordered, rigid arrays under certain conditions, but unsaturated fatty acids prevent such close packing and produce flexible, fluid aggregates. 

Circular dichroism (c.d.) spectroscopy measures the difference in absorption between left- and right-circularly polarized light by an asymmetric molecule. The spectrum results from the interaction between neighboring groups, and is thus extremely sensitive to the conformation of a molecule. Because the method may be applied to molecules in solution, it has become popular for monitoring the structure of biological molecules as a function of solvent conditions. 

Tetrahedral shapes dominate the structures of biological molecules, as our Box describes. 

C13-0034. Write a paragraph that describes the role of hydrogen bonding in the structures of biological macromolecules. 

Fig. 6.9 Characteristic structures of biological membranes. (A) The fluid mosaic model (S. J. Singer and G. L. Nicholson) where the phospholipid component is predominant. (B) The mitochondrial membrane where the proteins prevail over the phospholipids...

Abrahamson, S. A., and I. Pascher (Eds), Structure of Biological Membrane, Plenum Press, New York, 1977. 

Rosenberg, A. (1985), The Structure of Biological Science, Cambridge University Press, Cambridge, UK. 

Rose, S. (1998), Lifelines Biology Beyond Determinism, Oxford University Press, Oxford, UK. Rosenberg, A. (1985), The Structure of Biological Science, Cambridge University Press, Cambridge, UK. 

Stent, G. S. (1986), Glass bead game a review of The Structure of Biological Science (Alexander Rosenberg), Biol. Philos., 1, 227-247. 

Electron probe and X-ray fluorescence methods of analysis are used for rather different but complementary purposes. The ability to provide an elemental spot analysis is the important characteristic of electron probe methods, which thus find use in analytical problems where the composition of the specimen changes over short distances. The examination of the distribution of heavy metals within the cellular structure of biological specimens, the distribution of metal crystallites on the surface of heterogeneous catalysts, or the differences in composition in the region of surface irregularities and faults in alloys, are all important examples of this application. Figure 8.45 illustrates the analysis of parts of a biological cell just 1 pm apart. Combination of electron probe analysis with electron microscopy enables visual examination to be used to identify the areas of interest prior to the analytical measurement. 

Yeagle PL. T he Structure of Biological Membranes, CRC Press, Boca Raton, FL, 1991. 

Angersbach, A., Heinz, V., and Knorr, D. 2002. Evaluation of process induced dimensional changes in the membrane structure of biological cells using impedance measurement. Biotechnol. Progr. 18, 597-603. 

E. Th. Rietschel, L. Brade, U. F. Schade, U. Seydel, U. Zahringer, S. Kusumoto, and H. Brade, in E. Schrinner, M. Richmond, G. Seibert, and U. Schwartz (Eds.), Sutface Structures of Microorganisms and Their Interaction with the Mammalian Host Bacterial Endotoxins Properties and Structure of Biologically Active Domains, p. 1. Verlag Chemie, Weinheim, 1988. 

Advanced characterization of the structure, properties and function of the self-assembled precursor can be extrapolated from studies on the more robust crosslinked material, especially in changing or challenging environments, in which the assemblies would not remain intact. The introduction of crosslinks has aided in the maintenance of native conformations as a powerful technique during studies to determine the order and structure of biological assemblies [61, 62], Moreover, the robust characteristics that the crosslinks provide, combined with the ability to define their regioselectivity, are expected to expand the realm of possible applications for nanoscale materials. 

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