Eukaryotic cell cycle

See also Molecular Control of the Cell Cycle, The Cell Cycle, Eukaryotic DNA Polymerases (from Chapter 24)... 

Cell cycle Eukaryotic cell r cle (Tyson and Novak, 2001)... 

The eukaryotic somatic cell cycle is defined by a sequential order of tasks a dividing cell has to complete it must replicate its DNA, segregate its chromosomes, grow, and divide. The cell cycle can be divided into four discrete phases. DNA replication is restricted to S phase (DNA synthesis phase), which is preceded by a gap phase called G1 and followed by a gap phase called G2. During mitosis (M phase) the sister chromatids are segregated into two new daughter nuclei and mitosis is completed by the division of the cytoplasm termed cytokinesis (Fig. 1). 

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.

The size of egg cells demonstrates that higher eukaryotes have evolved ways to uncouple cell growth and cell cycle progression. The Drosophila egg is about 10 000-fold larger than the stem cells in the ovary. Much of the egg content is... 

The DNA is not reproduced exactly as the telomeres of later eukaryotes decrease in length with the cell cycle. Telomere reduction is environment dependent and does not happen in cancer cells. 

Murray and Hunt, 1993). Cyclins, kinases, and phosphatases that regulate the passage of the cell through the G] — S phase transition are all present in mammals, invertebrates, and plants (Solomon, 1993 Doonan and Fobart, 1997 Zavitz and Zipursky, 1997). However, multicellular eukaryotes contain multiple orthologs of yeast cell cycle proteins they initiate proliferation via growth factors, rather than, for example, yeast mating factors, and they possess additional checkpoint controls and repair pathways. 

The concept of the cell cycle (Figure 1-1-2) can be used to describe the timing of some of these events in a eukaryotic cell. The M phase (mitosis) is the time in which the cell divides to form two daughter cells. Interphase is the term used to describe the time between two cell divisions or mitoses. Gene expression occurs throughout all stages of interphase. Interphase is subdivided as follows ... 

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 ... 

---