Regulation external factors

The procedures for studying mechanisms of regulation of the rates of biochemical processes are described in Chapter 3. These procednres are applied to peptide synthesis in this discussion. There are three qnestions that must be answered prior to discussion of mechanisms, (i) Which reactions are non-eqnilibrium (ii) Which is the flnx-gen-erating reaction and how is it regulated (iii) What reactions other than the flnx-generating steps are regulated by external factors, i.e. external to the intermediates in peptide synthesis ... 

The regulated expression of inducible promoters offers advantages for selective activation of promoter activity in desired tissues. Activation can be achieved by either external factors (ionizing or non-ionizing radiations in the case of heat shock or radiation-inducible promoters), physiological characteristics unique to certain disease states, such as hypoxia in cancer, or the administration of non-toxic agents, such as glucose. 

Kemp, W.M., and Boynton, W.R. (1981) External and internal factors regulating metabolic rates of an estuarine benthic community. Oecologia 51, 19-27. 

In a mammalian cell, a large number (about 10 000) of mRNAs have a low abundance, i.e., a few copies per cell. Many strategies have been designed to enrich for specific mRNAs or to recognize certain clones (Section 2.5.2.2) otherwise many clones would have to be analyzed (Table 10.1). Subtractive hybridization depletes the sample of nonspecific mRNA in order to enrich for the mRNA sought. It is particularly suitable for isolating tissue-specific or developmental regulated sequences or clones derived from mRNA induced by external factors. 

Review of the effect of external factors on costs and returns on pharmaceutical R D, including new drug regulation, tax policy, product liability law, direct R D subsidies by the National Institutes of Health (NIH) and other government research bodies, and reimbursement policies (both private and public) for prescription drugs. 

Membran systems are known to play an important role in functioning biological objects (in mass transfer processes, passive and active transport of substance, regulation of an endocellular metabolism, in bio-energetics, etc.). Unique properties of biomembranes are caused by their structure, in particular, presence of bimolecular focused layers of lipids. At the same time, one of the main disadvantages of modelling lipid membran systems (monolayers, flat bilayers, liposomes), is their low stability in time and to action of external factors. 

Polar and hydrophobic residues lining the center of the bundle form a channel in the membrane, but as with bac-teriorhodopsin virtually all of the amino acids on the exterior of the membrane-spanning domain are hydrophobic. In many ion channels, external factors (e.g., a ligand, voltage, or mechanical strain) regulate ion flow across the bilayer by reorienting the helices. Details of ion channels and their structures are discussed in Chapter 7. 

Consider the behavior of the variable x shown in Figure 1.5. Notice that at time t = t0 the constant value of x is disturbed by some external factors, but that as time progresses the value of x returns to its initial value and stays there. If x is a process variable such as temperature, pressure, concentration, or flow rate, we say that the process is stable or self-regulating and needs no external intervention for its stabilization. It is clear that no control mechanism is needed to force x to return to its initial value. 

Plant physiologists have, on the other hand, disregarded the role played by soil and have studied metal uptake in nutrient solutions, which should imitate soil solutions. This seems to be an opportune strategy, since there is often a positive relationship between metal content of the soil solution and plant uptake (Denaix et al, 2002). However, none of the methods presented above illustrate how plant roots may influence the release of metals from soil, and what proportion of these released metals are actually taken up by plants (Stoltz and Greger, 2002). How do plants regulate metal uptake, and how do external factors, such as soil metal levels, influence this regulation In addition, are there differences in efficiencies of metal uptake between various metals as well as between various plant genotypes ... 

However, factors regulating soluble silica activity in real systems remain poorly understood because several factors propagate their effects to conceal the secrets of silica s amazing diversity of influences. The factors are polymorph metastabUity (kinetic control of growth and dissolution) modified by poorly understood external influences on growth and dissolution and polymorph specific binding properties and influence on crystallization of other substances. 

CO2 flux and H2O flux pass through stomata. Stomatal aperture depends on both internal and external factors. As Wong et a/., 1979, pointed out, the capacity of the mesophyll tissue to fix carbon allows the regulation of stomatal conductance (gc) For instance, DCMU, an inhibitor of photosynthetic electron transport, modifies both mesophyll CO2 assimilation and stomatal conductance in such a way that the intercellular concentration of CO2 (Ci) remains proportional to the air CO2 concentration (Ca) ... 

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