Mechanisms of adaptation

Platt EJ, Dumin IP, Rabat D (2005) Kinetic factors control efficiencies of cell entry, efficacies of entry inhibitors, and mechanisms of adaptation of human immunodeficiency virus, J Virol 79 4347 356... 

A shift in temperature from 38 to 22 °C leads to desaturation of fatty acids in Anabaena variabilis [110], resulting in control of the fluidity of the plasma membrane. Mutants have been isolated in Synechocystis PCC 6803 that were defective in desaturation of fatty acids, and the growth rate of one of these mutants was much lower than that of the wild-type at 22 °C [112]. It turned out that the mutant strain had a mutation in the gene desA, and when the wild-type allele was introduced into the chilling-sensitive cyanobacterium Anacystis nidulans, it resulted in increasing the tolerance of that strain to low temperature [113]. These experiments nicely demonstrate the existence of a mechanism of adaptation to low temperature in a chilling-tolerant cyanobacterium. 

The origin of a malignant tumor is a random genetic mutation leading to the loss of mitotic control by the cells. Normal cells experience mutations regularly, and they are necessary mechanisms of adaptation that are strictly controlled. Malignant transformation, however, means a loss of control and a chaotic, uncontrolled growth. 

In this context it is natural to consider the potential adaptability of species, as investigated by Karpevich (1976). Knowledge gained in this field is, however, far from satisfactory and we continue to underestimate the ability of species to adapt to extreme conditions. This aspect acquires special significance because of the increasing pollution of water bodies by human activities, so biochemical mechanisms of adaptation must become the object of much future study. 

Kreps, E.M., "fyurin, V.A., Gorbunov, N.V., Maksimovich, A.A., Polyakov, V.N., Plyusnin, V.V. and Kagan, V.E. (1986). Activation of peroxidase oxidation of lipids during migrational stress in gorbuscha possible mechanism of adaptation (In Russian). Doklady Akademii Nauk SSSR 286,1009-1012. 

Zaks, M.G. and Sokolova, M.M. (1961). On the mechanisms of adaptation to the water salinity in sockeye salmon (In Russian). Voprosy Ikhtiologii 1,331-338. 

In addition to this basic challenge that affects all experimental biologists faced with the need to dissect out a tractable study system, there is a further problem linked to the concept of trait that arises for the biochemist interested in elucidating mechanisms of adaptation and describing these adaptations in a logically consistent manner. To appreciate the nature of this... 

Levin, B.R., and C.T. Bergstrom (2000). Bacteria are different Observations, interpretations, speculations, and opinions about the mechanisms of adaptive evolution in prokaryotes. Proc. Natl. Acad. Sci. USA 97 6981-6985. 

Kimura s theory has not been universally accepted, and the debate between selectionism and neutralism is still going on, but the experimental data have changed for good our view of molecular evolution. Today, biologists are aware that neutral mutations are a fact of life, and that genetic drift is, at the molecular level, at least as important, if not more important, than natural selection. It must also be noticed that this does not diminish in the least the key role of natural selection in phenotypic evolution, and Kimura himself explicitely acknowledged that The basic mechanism of adaptive evolution is without doubt natural selection. He added however that Underneath the remarkable procession of life and indeed deep down... 

Our study was initiated because the mechanism of adaptation is still obscure, and much additional information is needed concerning the relationship between cholinesterase activity and the acetylcholine content of the central nervous system during the adaptation process. We also desired to investigate the possibility that adaptation might involve compensatory changes in the production or release of neural mediators, other than acetylcholine, capable of modifying the effects of high levels of the latter within the central nervous system. Norepinephrine was the first such mediator selected for study. 

On the other hand, microorganisms and herbivores rely on plants as a food source. Since both have survived, there must be mechanisms of adaptations toward the defensive chemistry of plants. Many herbivores have evolved strategies to avoid the extremely toxic plants and prefer the less toxic ones. In addition, many herbivores have potent mechanisms to detoxify xenobiotics, which allows the exploitation of at least the less toxic plants. In insects, many specialists evolved that are adapted to the defense chemicals of their host plant, in that they accumulate these compounds and exploit them for their own defense. Alkaloids obviously function as defense molecules against insect predators in the examples studied, and this is further support for the hypothesis that the same compound also serves for chemical defense in the host plant. 

Ausili A, Cobucci-Ponzano B, Di Lauro B, D Avino R, Perugino G, Bertoli E, Scire A, Rossi M, Tanfani F, Moracci M. A comparative infrared spectroscopic study of glycoside hydrolases from extremophilic archaea revealed different molecular mechanisms of adaptation to high temperatures. Proteins 2007 67 991-1001. 

Stratford, M. and Lambert, R.J.W. 1999. Weak-acid preservatives Mechanisms of adaptation and resistance by yeasts. Food Australia 51 26-29. 

Until now, we have dealt solely with changes to the enzyme molecule as the mechanism of adaptation, but enzyme function and stability can also be strongly influenced by the composition of the intracellular milieu in which the enzyme... 

Figure 1. Patterns of substrate disappearance related to mechanism of adaptation. Genetic changes such as mutation, plasmid exchange, or recombination (A). Growth of a small population of bacteria able to degrade the test chemical immediately (B). Delayed induction of enzymes or activation of specific organisms (C).

A combination of intra- and extrathyroidal mechanisms of adaptation leads to the preferential synthesis and secretion of T3 over T4, as a consequence of which circulating T3 levels are normal, or even increased, at the expense of decreasing circulating T4 concentrations. Circulating T3 only decreases in simations of very severe ID. 

One of the first steps in revealing the mechanism of adaptation was the finding that CheR-mediated MCP methylation (Section 7.3) and CheB-mediated demethylation (Section 7.2) are involved in adaptation (for a review, see reference [685]). The basis for the linkage between the... 

A common denominator for the methylation-dependent adaptation and the CheZ-dependent termination or adaptation is that both processes are triggered by changes in the phosphorylation level of CheY. It appears that the complete mechanism of adaptation, methylation-dependent and independent, is still not fully resolved. Methylation-independent adaptation was also demonstrated in B. subtilis, where it was found to be very effective [366]. 

In some cases, the animals simply sequester the toxic compounds in certain regions of their body without adverse effects. In others, sophisticated mechanisms of adaptation have evolved. 

Like other mammals, men had to develop mechanisms of adaptation and defenses against the environment. When these adaptation and defense mechanisms are overwhelmed, humans lose their health. 

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