Eukaryotes cell cycle

Fig. 2.2 Landmark events in the cell cycle of Saccharomyces cerevisiae. Gl, S, G2 and M are the classical phases of the eukaryotic cell cycle.

Figure 1. The cell cycle as a Cdc2 cycle. Progression through the eukaryotic cell cycle is sensitive to the phosphorylation state of Cdc2. A block to DNA synthesis (S) prevents dephosphorylation, and hence activation, of Cdc2. Impaired spindle function will prevent deactivation of Cdc2 and thus blocks exit from M phase (Hoyt et al., 1991 Li and Murray, 1991 reviewed in Nurse, 1991). Exit from M phase requires destruction of the regulatory subunit, Cyc B. Dephosphorylation of Cdc2 at thr-161 may act to destabilize the Cdc2/Cyc B complex and thus allow the ubiquitination of Cyc B followed by its destruction.

Each eukaryotic chromosome contains one linear molecule of DNA having multiple origins of replication. Bidirectional replication occurs by means of a pair of replication forks produced at each origin. Completion of the process results in the production of two identical linear molecules of DNA. DNA replication occurs in the nucleus during the S phase of the eukaryotic cell cycle. The two identical sister chromatids are separated om each other when the ceU divides during mitosis. 

Loss of purine or pyrimidine AP endonudease G2 phase of eukaryotic cell cycle ... 

J. J. Tyson and B. Novak, Regulation of the eukaryotic cell cycle Molecular antagonism, hysteresis, and irreversible transitions. J. Theor. Biol. 210, 249-263 (2001). 

FIGURE 12-41 Eukaryotic cell cycle. The durations (in hours) of the four stages vary, but those shown are typical. 

The eukaryotic cell cycle (see Fig. 12-41) produces remarkable changes in the structure of chromosomes (Fig. 24-25). In nondividing eukaryotic cells (in GO) and those in interphase (Gl, S, and G2), the chromosomal material, chromatin, is amorphous and appears to be randomly dispersed in certain parts of the nucleus. In the S phase of interphase the DNA in this amorphous state replicates, each chromosome producing two sister chromosomes (called sister chromatids) that remain associated with each other after replication is complete. The chromosomes become much more condensed during prophase of mitosis, taking the form of a species-specific number of well-defined pairs of sister chromatids (Fig. 24-5). 

Ubiquitin-dependent proteolysis is as important for the regulation of cellular processes as for the elimination of defective proteins. Many proteins required at only one stage of the eukaryotic cell cycle are rapidly degraded by the ubiquitin-dependent pathway after completing their function. The same pathway also processes and presents class I MHC antigens (see Fig. 5-22). Ubiquitin-dependent destruction of cyclinis critical to cell-cycle regulation (see Fig. 12-44). The E2 and E3 components of the ubiquitination cascade pathway... 

The effects of chromosome structure on gene regulation in eukaryotes have no clear parallel in prokaryotes. In the eukaryotic cell cycle, interphase chromosomes appear, at first viewing, to be dispersed and amorphous (see Figs 12-41, 24-25). Nevertheless, several forms of chromatin can be found along these chromosomes. About 10% of the chromatin in a typical eukaryotic cell is in a more condensed form than the rest of the chromatin. This form, heterochromatin, is transcriptionally inactive. Heterochromatin is generally associated... 

McKinney, J. D., and N. Heintz, Transcriptional regulation in the eukaryotic cell cycle. Trends Biochem. Sci. 16 430-434, 1991. 

Nigg, E. A., 1995, Cyclin-dependent protein kinases key regulators of the eukaryotic cell cycle. 

Fig. 1. The eukaryotic cell cycle. The S phase is typically 6-8 h long, G2 is a phase in which the cell prepares for mitosis and lasts for 2-6 h, mitosis itself (M) is short and takes only about 1 h. The length of G, is very variable and depends on the cell type. Cells can enter G0, a quiescent phase, instead of continuing with the cell cycle.

S The part of interphase of the eukaryotic cell cycle when DNA is replicated. 

Chassagnole, C., Jackson, R.C., Hussain, N., Bashir, L., Derow, C., Savin, J., Fell, D.A. Using a mammalian cell cyde simulation to interpret differential kinase inhibition in anti-tumour pharmaceutical development. BioSystems 2006, 83 91-97. Csikasz-Nagy, A., Battogtokh, D., Chen, K.C., Novak, B., Tyson, J.J. Analysis of a generic model of eukaryotic cell-cycle regulation. Biophys J. 2006,90 4361-4379. Smith, J.A., Martin, L. Do cells cycle ... 

Know the stages in the eukaryotic cell cycle and the more important biochemical events in each stage. 

A typical eukaryotic cell cycle is shown in Figure 13.3. Following mitosis and cytokinesis, the daughter cells begin the interphase of a new cycle with the Gj (gap 1) phase in which biosynthetic activities markedly increase. The G phase is... 

Figure 13.3 Typical eukaryotic cell cycle. M, mitotic phase Gx, gap phase S, synthesis phase G2, gap phase 2. The percentage of times shown for each phase are ranges for cells with cell cycle times of approximately 24 h.

Fig. 16-4 The eukaryotic cell cycle. The durations of the four phases as shown are typical of higher eukaryotic cells growing in tissue culture.

Csikasz-Nagy A, Battogtokh D, Chen KC, Novak B, Tyson JJ. Analysis of a generic model of eukaryotic cell-cycle regulation. Biophys. J. 2006 90 4361-4379. 

Figure 27.34. Eukaryotic Cell Cycle. DNA replication and cell division must take place in a highly coordinated fashion in eukaryotes. Mitosis (M) takes place only after DNA synthesis (S). Two gaps (Gj and G2) in time separate the two processes.

Analyses of in situ DNA synthesis of Euglena gracilis identify zinc-dependent steps in the eukaryotic cell cycle and show that the derangements in RNA metabolism are critical determinants of the growth arrest associated with zinc deficiency. Combined use of microwave-induced emission spectrometry and micro gel emulsion chromatography shows the presence of stoichiometric amounts of zinc essential to the function of E. gracilis and yeast RNA polymerases, the reverse transcriptases" from avian myeloblastosis, murine leukemic and woolly type C viruses, and E. coli methionyl tRNA synthetase. These results stress the importance of zinc to both nucleic acid and protein metabolism. Transient-state kinetic studies of carboxypeptidase A show that zinc functions in the catalytic step of peptide hydrolysis and in the binding step of ester hydrolysis. 

The eukaryote cell cycle is composed of the following four phases M phase, mitosis phase (gap 1), between mitosis and initiation of DNA synthesis S phase, DNA synthesis and phase (gap 2), cell growth and macromolecule synthesis. 

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