Biological macromolecules mechanical properties

The application of NMR to the understanding of polymer properties has had a long history. The technique has allowed a powerful insight into the nature of the polymer chain and the nature of the dynamics of the polymer [133]. Case [134] reviewed the impact that quantum mechanics has had in interpreting NMR for biological macromolecules. Here we consider through some examples the impact... 

Alves, M.M., Antonov, Yu.A., Goii9alves, M.P. (2000). Phase equilibria and mechanical properties of gel-like water-gelatin-locust bean gum systems. International Journal of Biological Macromolecules, 27, 41 17. 

The radiation pressure exerted by light is very weak. A bright laser beam of several milliwatts of power can exert only a few piconewtons (pN) of force. However, a force of 10 pN is enough to pull a cell of E. coli through water ten times faster than it can swim.213 In about 1986, it was found that a laser beam focused down to a spot of - one K ( 1 pm for an infrared laser) can trap and hold in its focus a retractile bead of 1 pm diameter. This "optical tweezers" has become an important experimental tool with many uses.213 214 For example, see Fig. 19-19. Not only are optical tweezers of utility in studying biological motors but also mechanical properties of all sorts of macromolecules can be examined. For example, DNA can be stretched and its extensibility measured.215 Actin filaments have even been tied into knots 216... 

Cellulose, an important constituent of wood, has long chains of glucose molecules linked by glycoside bonds. These chains are cross-linked by hydrogen bonds. Many biological polymers have unusual mechanical properties, not at present matched by the properties of artificial macromolecules. For instance, arteries are... 

Silver FH. Self-assembly of connective tissue macromolecules. In Biological Materials Structure, Mechanical Properties, and Modeling of Soft Tissues. New York NYU Press, 1987 Chapter 5,150-153. 

Tissues are composites of macromolecules, water, ions, and minerals, and therefore their mechanical properties fall somewhere between those of random coil polymers and those of ceramics. Table 6.1 lists the static physical properties of cells, soft and hard tissues, metals, polymers, ceramics, and composite materials. The properties listed in Table 6.1 for biological materials are wide ranging and suggest that differences in the structure of the constituent macromolecules, which are primarily proteins, found in tissues give rise to the large variations in strength (how much stress is required to break a tissue) and modulus (how much stress is required to stretch a tissue). Because most proteins are composed of random chain structures, a... 

The key components in all sophisticated biological materials are the macromolecules that the cells produce and subsequently incorporate into the material. These include proteins, glycoproteins, proteoglycans, lipid assemblies and polysaccharides. Many biological materials are composed almost entirely of these assembled macromolecules. Common examples are the cuticles of many insects, the skin and tendons of vertebrates or the silk of spider webs. A very widespread adaptation is to stiffen the material by the introduction of a mineral phase. Common mineralized biological materials include the shells of mollusks, the carapaces of crustaceans, and the bones and teeth of vertebrates. Many of them are composite materials and are known to possess remarkable mechanical properties, especially when taking into account that they form at ambient temperatures and pressures, and that their mineral components are often commonplace materials with rather poor natural mechanical properties... 

Photochromic control of the polymer properties leads to potential applications involving the mechanical properties of a solution (viscosity, photogelation), polymer fiber (extensibility, photomuscle ), or membrane (porosity). More important, however, the ability to control the activity of enzymes and other biologically important macromolecules leads to potential applications in clinical phototherapy. 

At the theoretical level, full quantum mechanical calculations on biologic macromolecules are not computationally feasible, nor would they be particularly helpful in understanding macro-molecular properties without proper inclusion of the solvent water or other biologic matrix on which these properties so intimately depend. However, ab initio quantum mechanical calculations on smaller systems that represent crucial steps in an enzymic reaction, for example, can be helpful in understanding specific processes within macromolecules or in estimating intermolecular forces and stereochemical effects in molecular mechanics simulations that are not experimentally accessible. 

Proteins are unique among the biological macromolecules and have attracted active interest from various disciplines. For the physicist it is the structure that has the characteristics of order as well as of disorder. The chemist is attracted by the unique properties that show up in the catalytic activity of enzymes and in the conversion of chemical into mechanical energy in muscle. Biologists tend to put the emphasis on the functional role of proteins. 

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