Molecular mechanics, type selection

The literature contains a wide choice of functions and parameters for including hydrogen bonding in molecular mechanics. A selection is given in Box 4.4. All distinguish between different types of hydrogen bonds, and some are developed for particular classes of molecules. 

The calculations described here have been called strain calculations, molecular mechanics, or force field calculations. We prefer the latter term. For a discussion of historical developments and a literature survey of earlier work, which are not given here, the reader is referred to a number of other reviews (1-3). The present paper deals with the description of force field types, techniques of energy minimisation, and procedures for the determination of force field parameters, and with some applications, preferentially taken from our own field of interest. In accordance with the experiences of the author, the work of Lifson and coworkers is given special attention other authors are nevertheless well represented in the context of critical comparisons. We hope that this selection, although inevitably biased, will help to improve the consistency of the presentation of the subject. 

Fig. 5. A multipathway mechanism of action for insulin. Insulin exerts a plethora of actions on target tissues and it is extremely difficult to visualize a single second message acting to achieve all such effects. Here it is suggested that a number of signals emanate from the plasma membrane as a consequence of insulin binding to its receptor. This may also offer a molecular explanation for selective insulin-resistant states noted in type-1 and type-II human diabetes as well as experimentally in animals. In such circumstances lesions could occur at particular points on this multipathway .

As we begin to unravel the molecular mechanisms of the regulation of anthocyanin biosynthesis, we must remember that evolution and selection had significant opportunities to explore new ways to color plants, flowers, and seeds. Model plant systems such as maize, petunia, and Arabidopsis will continue to provide the framework to understand how pigment accumulation is controlled. However, it is important to investigate how nature has exploited variations in these central prototypes to provide the amazing diversity found today in the type and distribution of anthocyanin pigments. 

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