Transition review

The cell cycle contains critical events where the cell switches from one state of biochemical activity to another state, in an irreversible maimer. These events are called cell cycle transitions. Often, activating and inhibitory signals are received and transmitted at these cell cycle transitions (review Nurse, 1994 Heichman, 1994 Elledge, 1996) (Fig. 13.3). 

Of the various CKls, plh has a central role in regulation of the phosphorylation status of pRb and in the Gl/S transition (review Sherr, 1996). Investigations in tumor cells indicate that proteins coded by the pl6 gene locus fimction as tumor suppressors and are of great importance for tumor development (review Chin et al., 1998). 

An important decision for the entry into mitosis is taken at the G2/M transition (review Smits and Medema, 2001). At this point, the cell cycle can be arrested if the DNA is not properly replicated or is damaged. Therefore, the G2/M transition functions as an important checkpoint for progression through M phase. 

Involved in transitional reviews in year 9 for statemented pupils. 

Imada, M., Fujimori, A., Tokura, Y. (1998). Metal-insulator transitions. Reviews of Modem Physics, 70, 1039-1263. 

A catalyst may play an active role in a different sense. There are interesting temporal oscillations in the rate of the Pt-catalyzed oxidation of CO. Ertl and coworkers have related the effect to back-and-forth transitions between Pt surface structures [220] (note Fig. XVI-8). See also Ref. 221 and citations therein. More recently Ertl and co-workers have produced spiral as well as plane waves of surface reconstruction in this system [222] as well as reconstruction waves on the Pt tip of a field emission microscope as the reaction of H2 with O2 to form water occurred [223]. Theoretical simulations of these types of effects have been reviewed [224]. 

The liquid-crystal transition between smectic-A and nematic for some systems is an AT transition. Depending on the value of the MacMillan ratio, the ratio of the temperature of the smectic-A-nematic transition to that of the nematic-isotropic transition (which is Ising), the behaviour of such systems varies continuously from a k-type transition to a tricritical one (see section A2.5.91. Garland and Nounesis [34] reviewed these systems in 1994. 

Section BT1.2 provides a brief summary of experimental methods and instmmentation, including definitions of some of the standard measured spectroscopic quantities. Section BT1.3 reviews some of the theory of spectroscopic transitions, especially the relationships between transition moments calculated from wavefiinctions and integrated absorption intensities or radiative rate constants. Because units can be so confusing, numerical factors with their units are included in some of the equations to make them easier to use. Vibrational effects, die Franck-Condon principle and selection mles are also discussed briefly. In the final section, BT1.4. a few applications are mentioned to particular aspects of electronic spectroscopy. 

Often it is possible to resolve vibrational structure of electronic transitions. In this section we will briefly review the symmetry selection rules and other factors controlling the intensity of individual vibronic bands. 

Accurate enthalpies of solid-solid transitions and solid-liquid transitions (fiision) are usually detennined in an adiabatic heat capacity calorimeter. Measurements of lower precision can be made with a differential scaiming calorimeter (see later). Enthalpies of vaporization are usually detennined by the measurement of the amount of energy required to vaporize a known mass of sample. The various measurement methods have been critically reviewed by Majer and Svoboda [9]. The actual teclmique used depends on the vapour pressure of the material. Methods based on... 

Williams 1 H 1993. Interplay of Theory and Experiment in the Determination of Transition-State Structures. Chemical Society Reviews 1 277-283. 

Reviews of transition state theory and variational transition state theory are... 

Review artieles pertinent to transition metal modeling are... 

Molecular meclianics techniques for transition metals are reviewed in... 

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