Structure of living systems

We have already seen that around 70% of the human body is water and this should be no surprise since, following development of the primeval cells in the oceans, evolution has continued within an aqueous environment and exploited the unique properties of water to the best advantage to living systems. Water is the only naturally occurring inorganic liquid and is the only compound which occurs in nature in all three physical states of matter solid, liquid, and gas. The omnipotence of the roles of water in the human body may be seen by reference to Table 1.1. Water is used to provide bulk to the body and use is also made of its unusual chemical properties. 

The high specific heat of water enables it to act as a heat buffer, thus minimizing the effects on the cells of fluctuations in environmental temperature. The high latent heat of vaporization permits humans to use the evaporation of sweat as a cooling mechanism. 

Many important properties of macromolecules depend on their interactions with water molecules. Water, being dipolar in nature, is a very good solvent for a wide variety of solids. Most ionic compounds, of course, dissolve because the ion solvation contributes enough energy to disrupt the crystal lattice structure. Polar compounds, e.g. alcohols, aldehydes, and ketones, dissolve due to the ability of water to form 

The control of the degree of ionization of water is of crucial importance, with the following reactions being most important  

Biological membranes and the active sites of enzymes may be considered as special types of solvents in their own right. In the membranes, phospholipid, protein, and carbohydrate molecules make up a system through which both ionic and non-ionic species must pass, some by simple diffusion, others by some form of specific active transport. At the active sites of enzymes, exceptional conditions exist which permit substrates to be held in stereochemical forms which modify the chemical activity, but which would be extremely unstable in aquo. 

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Coveney, P. and High field, R. (1991). The Arrow of Time . Ballantyne Books, New York. Cramer, F. (1993). Chaos and Order. The Complex Structure of Living Systems . VCH,... 

F. Cramer, Chaos and Order, The Complex Structure of Living Systems, VCH, Weinheim, 1993, Chap. 7. 

When one looks at the macroscopic structure of living systems, what one is really seeing is the cooperative activity of cells of different types communicating by different molecules. 

The synunetry of D. is observed for most natural biopolymers, which show only shear piezoelectricity. The 3 axis is taken as the axis of orientation. In this symmetry the lelaboo da s -d holds. The symmetry of C. is found in certain structures of living systems such as bone and tendon. The preferred alignment of the polar axis of polymer crystallites in the 3 axis provides the piezoelectric constants d d as well as the pyroelectric effect in the 3 axis, although they are not so large. 

Cramer F (1993) Chaos and order. The complex structure of living system. VCH, Weinheim... 

Deoxyribonucleic acid (DNA) is a very important biopolymer with the function of storage and transmission of genetic information. In this reason the protection of structural integrity and functional activity of DNA is essential for the viability of living systems, as well as the effectiveness of laboratory DNA-technics. 

Biochemistry can be defined as the science concerned with the chemical basis of life (Gk bios life ). The cell is the structural unit of living systems. Thus, biochemistry can also be described as the science concerned with the chemical constituents of living cells and with the reactions and processes they undergo. By this definition, biochemistry encompasses large areas of cell biology, of molecular biology, and of molecular genetics. 

Zampieri, G. G., Jackie, H., and Luisi, P. L. (1986). Determination of the structural parameters of reverse micelles after uptake of proteins. J. Phys. Chem., 90, 1849. Zeleny, M. (1977). Self-organization of living systems formal model of autopoiesis. Int. J. Gen. Sysl, 4, 13-28. 

In conclusion, biomacromolecules have evolved to be big because from their size and structural variety arise a number of emergent properties that allow them not only to function with utmost efficiency, but to do so in a manner fully controlled by the higher levels of complexity characteristic of living systems (see Section 2.4). 

In addition to self-assembly of protein structures, in living systems the complex maneuvers needed to achieve properly folded tertiary structures are facilitated by the function of a pre-existing protein machinery, of which, ihe molecular chaperones are an illustrative example. Chaperones are proteins that bind to and stabilize an otherwise unstable conformer of another protein, and by controlled binding and release, facilitate its correct fate in vivo. Molecular chaperones may be said to be the natural... 

These molecules are mostly found in cells, the basic structural units of living systems, or in close proximity to cells. 

The process dynamics is complex. Typical response times vary from a few seconds up to weeks and months. Nonlinear phenomena are common due to large disturbance amplitudes. Measurement and transport time delays cannot be neglected. Sensor location is important due to spatial distributions. As living organisms are part of the system, not only parameters but the structure of the system dynamics can be changed during the operation. 

The origin of some products of biotechnology from certain types of living systems or cells carries potential risks of diverse types due to the potential transmission of infectious organisms or prions from the producing system. So far at least few of these products have been manufactured by chemical synthesis, because of the chemical and structural complexity, although that route may become more important in the future. 

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