Backbones living systems

Why Do We Need to Know This Material The elements in the last four groups of the periodic table illustrate the rich variety of the properties of the nonmetals and many of the principles of chemistry. These elements include some that are vital to life, such as the nitrogen of proteins, the oxygen of the air, and the phosphorus of our bones, and so a familiarity with their properties helps us to understand living systems. Many of these elements are also central to the materials that provide the backbone of emerging technologies such as the nanosciences, superconductivity, and computer displays. 

The fact that enzymes employ dynamics, should in no way be surprising -evolution knows nothing of quantum mechanics, classical mechanics, or vibration-ally enhanced tunneling. Rates of reaction are optimized for living systems using all physical and chemical mechanisms available. It is also important to point out that such protein dynamics are far from the only contributor to the catalytic effect. In fact in an enzyme such as alcohol dehydrogenase, transfer of a proton from the alcohol to the coordinated zinc atom is critical to the possibility of the reaction. The specific modulation of the chemical barrier to reaction via backbone protein dynamics is now seen to be part of the chemical armamentarium employed by enzymes to catalyze reactions. 

Block copolymers characterised by different backbone structures of well-defined block lengths have been obtained from oxiranes and other heterocyclic monomers in the presence of catalysts that are effective at bringing about living polymerisations. Aida et al. [127,188,189,195,196] applied aluminium porphyrins and Teyssie et al. [125,197,198] applied bimetallic /i-oxoalkoxidcs for block copolymerisations in systems involving oxirane lactone, oxirane oxirane/cyclic acid anhydride, and oxirane/cyclic acid anhydride lactone as block forming units and obtained respective polyether polyester and polyester polyester block copolymers. Such copolymers seem to be of exceptionally wide potential utility [53]. 

Water, however, carries both nucleophilic and electrophilic centers. This means that water reacts with many biomolecules in a way that damages them. In the case of proteins, as noted above, water reacts with the amide backbone to degrade proteins, generating amino acids as hydrolysis products (see Figure 2.13). This can be disadvantageous if the protein is desired, as it requires that the protein be re-synthesized. The turnover of proteins is important, however, in any system living in a dynamic environment. Thus, the hydrolytic instability of proteins in water is key to maintaining life. 

Derivatives of phosphoric acid, pyrophosphoric acid, and related compounds are very important in biological systems. Pyrophosphoric acid is an anhydride of phosphoric acid. Adenosine triphosphate, an energy carrier that is universally found in living organisms, has a phosphorus dianhydride connected to an adenosine group by a phosphate ester linkage. Phosphorus ester bonds are used to form the polymeric backbone of DNA (see Chapter 27). 

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