Polymers in Living Systems

With these difficulties in mind, it is instructive to look at main biological macromolecules - proteins, DNA, and RNA - that have precise and specific structures. These polymers in living systems are responsible for functions, which are incomparably more complex and diverse than the functions that we... 

Chain transfer is far more important than in the anionic case, so we do not encounter living polymers in cationic systems. 

Siik is just one exampie of macromoiecuies, aiso known as poiymers. Macromoiecuies are the subject of this chapter. The principies introduced in Chapters 9-11 help to explain the properties of these molecules, many of which are carbon-based. In this chapter, we outline the principles of the stmcture and synthesis of the major classes of macromoiecuies and describe the properties that give these chemical substances central roles in industrial chemistry and biochemistry. We describe the components from which macromoiecuies are constmcted, some important industrial polymers, and the macromoiecuies found in living systems. 

Plants and animals synthesize a number of polymers (e.g., polysaccharides, proteins, nucleic acids) by reactions that almost always require a catalyst. The catalysts present in living systems are usually proteins and are called enzymes. Reactions catalyzed by enzymes are called enzymatic reactions, polymerizations catalyzed by enzymes are enzymatic polymerizations. Humans benefit from naturally occurring polymers in many ways. Our plant and animal foodstuffs consist of these polymers as well as nonpolymeric materials (e.g., sugar, vitamins, minerals). We use the polysaccharide cellulose (wood) to build homes and other structures and to produce paper. 

In this section, enzymes in the EC 2.4. class are presented that catalyze valuable and interesting reactions in the field of polymer chemistry. The Enzyme Commission (EC) classification scheme organizes enzymes according to their biochemical function in living systems. Enzymes can, however, also catalyze the reverse reaction, which is very often used in biocatalytic synthesis. Therefore, newer classification systems were developed based on the three-dimensional structure and function of the enzyme, the property of the enzyme, the biotransformation the enzyme catalyzes etc. [88-93]. The Carbohydrate-Active enZYmes Database (CAZy), which is currently the best database/classification system for carbohydrate-active enzymes uses an amino-acid-sequence-based classification and would classify some of the enzymes presented in the following as hydrolases rather than transferases (e.g. branching enzyme, sucrases, and amylomaltase) [91]. Nevertheless, we present these enzymes here because they are transferases according to the EC classification. 

During the last two decades, chemists have become increasingly focused on how molecules interact, i.e. on supramolecular chemistry. Dynamic intermolecular processes provide opportunities for incorporation of control, adaptation and function in man-made materials, as observed in living systems. In biology, these processes are tightly controlled by the catalytic action of enzymes. In this chapter, we focus on enzymatically controlled supramolecular polymerisation, whereby self-recognising molecular building blocks assemble to form extended onedimensional (ID) structures, or supramolecular polymers, with unique adaptive features. 

Why are isotonic drinks useful Osmotic pressure in living systems is incredibly important yet how often is the topic dismissed or merely discussed as a means to measure molecular weight of polymers Why not consider polymers as biological macromolecules and add to the discussion that a balance of osmotic pressure keeps our cells from bursting - which goes back to why the isotonic sport drinks are useful Relevance in the examples used in our courses is possible. 

Carbohydrates form the major structural components of the cell walls. The most common form is cellulose which makes up over 30 per cent of the dry weight of wood. Other structural forms are hemicellulose (a mixed polymer of hexose and pentose sugars), pectins and chitin. Apart from contributing to the structure, some polymers also act as energy storage materials in living systems. Glycogen and starch form the major carbohydrate stores of animals and plants, respectively. Carbohydrate structure, like that of nucleic acids and proteins, is complex, and various levels of structure can be identified. 

The potentially beneficial properties of antioxidants have been a common subject in the popular press. Such compounds have the ability to eliminate toxic free radical species in living systems. Antioxidants are claimed to have cytoprotective properties in the inhibition of cancer, heart disease, and various skin disorders, and are often simply labeled as antiaging. There is a host of benzofuran examples in the recent literature that find application in all of these areas as potential pharmaceuticals, cosmetics, and polymer stabilizers. 

Initiation can be most effectively studied in systems with the smallest number of elementary steps in the polymerization reaction. This requirement is fulfilled in living systems (without termination and transfer) with monomers which do not generate polymer chains. By eliminating propagation (or suppressing it to dimerization) kinetically relatively simple systems can be obtained which are suitable for the application of convenient analytical methods. 

The synthetic copolymers described in the previous section are particularly simple molecules compared to the macromolecules that occur in living systems. Virtually all bio-polymers exhibit some amphiphilic character, due to the presence of polar and lipophilic patches in the single molecule. 

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