Metaphase state

FIGURE 24-5 Eukaryotic chromosomes, (a) A pair of linked and condensed sister chromatids from a human chromosome. Eukaryotic chromosomes are in this state after replication and at metaphase during mitosis, (b) A complete set of chromosomes from a leukocyte from one of the authors. There are 46 chromosomes in every normal human somatic cell. 

As it follows from the infrared spectra, only cyclic dimers are present in the crystal state on cooling to 100 K. In this state, the bond energy of the hydrogen bond has been determined to be 36 1 kJ/mol at 100 K and 34 1 kJ/mol at 300 K. The crystals, on being heated, exhibit the appearance of a new band (920-925 cm-1) well before the transition to a metaphase. The intensity of the band increases with T, and the maximum of the band slightly moves to low... 

As we mentioned in Section V, near the temperature of phase transition to the metaphase the solid state of alkyl- and alkoxybenzoic acids is unstable in relation to the formation of hydrogen-bonded open associates. The associates merge in polymer chains, which can include over 10 acid molecules. Let us treat how the statistical model described above can account for such a behavior of the associates. 

At metaphase, the spindle Is In a state of tension with forces pulling the two kinetochores toward the opposite spindle poles balanced by forces pushing the spindle poles apart. Sister chromatids do not separate because they are... 

Richmond and Phillips (1975) found in the case of Botrytis cinerea that the conidia of the fungi produced distorted germ tubes in the presence of benomyl. In most of the fungi, cell division differed from classical mitosis, the normal states of which were not seen clearly in any of the treated material. Chromosomes became visible at the prophase-metaphase, but they did not completely separate. Finally, the chromatin became stretched into long threads, daughter nuclei did not separate completely and chromatin was often present as irregular shaped masses. 

As discussed in section 10.6, the increase in Ca at fertilization appears to induce some phosphorylation event(s) via calmodulin-activated protein kinase (Lorca et al., 1993). One result of this is the activation of the cyclin degradation pathway, which releases the oocyte from metaphase arrest. A recent study in rabbit oocytes (Collas et at, 1995) was aimed at measuring MPF-associated kinase activity as a function of the number of Ca pulses applied to the oocytes. The results suggest that, whereas a single Ca pulse elicits only a transient decrease in MPF activity, a prolonged series of Ca spikes is needed to sustain the MPF inactivation associated with exit from the metaphase arrested state. 

The techniques for using the stamen-hair system have been developed over the past several years specifically for radiobiological studies. However, preliminary experiments indicate that these techniques are applicable to chemical mutagen studies in either a gaseous or liquid state. Several years ago. Smith and Lotfy ) showed that certain gaseous chemicals, specifically ethylene oxide, ketene, and methyl chloride, produced chromosome aberrations in pollen tubes of Tradescantia paludosa cultured to metaphase. More recent experiments have also employed microspores. 

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