Equilibrium cell division

X-ray interference patterns, cell division in sea urchins, equilibrium positions in crystals, Romanesque cathedrals, snowflakes, music, the theory of relativity.f... 

In addition to being an essential component of the mitotic spindle, and being required for the maintenance of cell shape, microtubules are involved in a wide variety of cellular activities, such as cell motility and communication between organelles within the cell. Any disruption of the equilibrium within the microtubule system would be expected to disrupt cell division and normal cellular activities in which microtubules are involved. 

Symmetry establishes a ridiculous and wonderful cousinship between objects, phenomena, and theories outwardly unrelated terrestrial magnetism, women s veils, polarized light, natural selection, the theory of groups, invariants and transformations, the work habits of bees in the hive, the structure of space, vase designs, quantum physics, scarabs, flower petals, X-ray interference patterns, cell division in sea urchins, equilibrium positions in crystals, Romanesque cathedrals, snowflakes, music, the theory of relativity. 

Paclitaxel acts by enhancing microtubule assembly and stabilizing microtubules (1,2). Microtubules consist of polymers of tubulin in dynamic equilibrium with tubulin heterodimers. Their principal function is the formation of the mitotic spindle during cell division, but they are also active in many interphase functions, such as cellular motility, intracellular transport, and signal transmission. Paclitaxel inhibits the depolymerization of tubulin, and the microtubules formed in the presence of paclitaxel are extremely stable and dysfunctional. This stabilization impairs the essential assembly and disassembly required for dynamic cellular processes, and death of the cell results through disruption of the normal microtubular dynamics required for interphase processes and cell division. In tumor cells, cytotoxicity is represented by the appearance of abnormal microtubular bundles, which accumulate during G2 and mitosis, blocking the cell cycle (3). 

The second view did not rely on the existence of an oscillator independent from mitosis and stated that the latter is an integral part of the mechanism underlying the cell division rhythm (Tyson Sachsenmaier, 1978, 1984). The rhythm would thus have a simpler origin, due to the discontinuity of cell division. Tyson Sachsenmaier (1978) compared such a rhythm to the effect of a thin stream of sand constantly falling on a pan on one side of a balance when a critical weight is reached, the pan tips over and, once emptied, recovers its equilibrium position. The sand then accumulates again until the next flip. In this phenomenon, the phase of abrupt decrease that precedes the replenishment phase consists of the discontinuous reversal of the position of the pan. This image could apply to the case of the mitotic cycle the latter could result from the accumulation of a mitotic factor up to a threshold beyond which the discontinuity of cell division would occur. No oscillation should take place in the absence of mitosis. 

Table V shows that some activity is observed for metal salts in lethality studies. These metal ions are not as active as the inert complexes in the lethality assay, and none of these ions has been found to be active in reversion studies. Perhaps the difference is that the metal ions rapidly come to equilibrium in the cell and form kinetically labile and non-toxic complexes with DNA. As strand separation occurs, the labile ions that are on the DNA can be rapidly displaced and thus are not able to interfere with replication. On the other hand, the inert ions undergo substitution at rates which are slow compared to cell division. When they undergo ligand substitutions and become attached to DNA, they remain fixed to the DNA long enough to cause errors during replication.

Table 1.1 Thermodynamic data, electrodes, electrolyte, cell reaction, equilibrium cell voltage, and specific energy of some customary primary-and secondary-battery systems. The theoretical specific energy, listed in Column 8 results from division of AG by the weight of the reacting components. The difference between these values and those observed in practice (Column 9) is caused by kinetic parameters.

The axisymmetric mode 1=2 shows new possibilities of oscillatory instabilities. It is interesting from the point of view of cell division and non-equilibrium stability of emulsions. 

The tubulin system plays a key role during mitosis and disturbing its dynamic equilibrium can prevent cell division and induce apoptosis. Microtubules, dynamic protein polymers composed of a-tubulin and P-tubulin heterodimers, are major components of the cytoskeleton with an important role in variety of cellular functions. They have become well-established cellular targets for... 

The reaction of X with S must be fast and reversible, close to if not at equilibrium with concentration of S. It can be that there is an intermediate step in which X binds to a protein kinase (a protein which phosphorylates other proteins mostly at histidine residues in bacteria) using phosphate transferred from ATP. It then gives XP which is the transcription factor, where concentration of S still decides the extent of phosphorylation. No change occurs in DNA itself. Here equilibrium is avoided as dephosphorylation involves a phosphatase, though changes must be relatively quick since, for example, cell cycling and division depend on these steps, which must be completed in minutes. We have noted that such mechanical trigger-proteins as transcription factors are usually based on a-helical backbones common to all manner of such adaptive conformational responses (Section 4.11). 

Division by 4.184joules/cal permits conversion to cal/°C. The voltages and across a standard resistor (Rg) and the heater R connected in series are the measiue-ments of interest, since i Rt, = VaVJRa- The heater can be used to advantage in hastening the cell to a thermal equilibrium with the thermostat bath and titrant by heating the cell and its contents to a temperature very close to that at which the thermostat is set. 

With no current through the electrolytic cell, it does not matter whether the electrodes are large or small the equilibrium potentials are the same. But with current flow, the current density and therefore the voltage drop and the polarization, will he much higher at the small electrode. An increased potential drop will occur in the constrictional current path near the small electrode, and in general the properties of the small electrode will dominate the results. The small electrode will be the electrode studied, often called the working electrode. It is a monopolar system, meaning that the effect is determined hy one electrode. The other electrode becomes the indifferent or neutral electrode. Note that this division is not true in potentiometry, electrode area is unimportant under no-current conditions. 

Motor molecules play a key role in muscular contraction, ceU division, and cell transport. Molecular motors are microscopic systems that move along one-dimensional periodic structures. They undergo several states, within each of which operates at local equilibrium on timescales small compared to the exchange rates between these states. For example, for the transient response of muscles, the fastest characteristic times of the motors are in the range of miliseconds. Thermal equilibrium occurs on length scales of around 10 nm after around 10 to 100 nanoseconds. The states of the proteins during muscular contraction therefore had to be in local equilibrium. Up to five or six different states could be involved (Julicher et al., 1997). 

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