Wobbly charges

With the exception of methionine, isoleucine, tryptophan and the unassigned triplet UGA, the charges + and — can be assigned to A, G, and U, C, respectively. For those bases where only one aminoacid appears one can adopt the alternate assignment given in the wobble theory. 

Fortunately, the imino forms of A and C and the enol forms of G and T occur rarely. Most A C and G T mispairs observed to date in high-resolution crystal structures (e.g., References 22 and 23) associate through a wobble configuration (14), with the bases sheared past one another relative to the Watson-Crick configuration (Table 1 and Fig. 1). These structural perturbations (Table 1 and Table 2) alter the patterns of atomic charges and accessibihty that are presumably required for protein recognition and enzymatic action (see discussion below). 

As is shown in Fig. 54 the electrons emitted from a hidden hot filament and accelerated in the electrical field are deflected by, say, 270° magnetically with this type of gun and thus focused to the evaporation material. Small amounts of evaporated material from the hot filament cannot contaminate the films. A high voltage in the range between 6 - 10 kV accelerates the electrons in the direction to the anode that is the crucible. The size of the focal spot can be varied by variation of the Wehnelt potential and in addition there is an electromagnetic X-Y sweep. The first is particularly important when metals and dielectric materials have to be evaporated in the same charge. Since the power densities of some 10 kW cm 2 required for metals would destroy most of the dielectrics, a wobble modulation of the focused beam is inadequate, and dielectric materials must be evaporated by a soft evidently defocused electron beam. The required power density is about 1 - 2 kW cm 2. 

This effect may be explained in terms of the quantum theory of electrodynamics. According to this theory each mode of the quantized radiation field possesses a zero-point energy of hu)/2. This implies that, even in the absence of external radiation, the mean square value of the time-depen-dent electric field is finite and that a hydrogen atom will experience a perturbation produced by the fluctuations in this field. These zero-point fluctuations cause the electron to wobble randomly in its orbit and so smear the charge over a greater volume of space. Since the electron is bound to the nucleus by a non-uniform electric field, the reduction in electron density causes a shift in the atomic energy levels. This Lamb shift, as it is now called, is greatest for those states in which iK0) is finite, i.e. the n states. 

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