o Reproduction growth and development and tissue renewal CHAPTER 12 13 Cell cycle and division Somatic cells Gametes o Have 2 sets of chromosomes diploid o Nonreproductive o Reproductive cells o One set of chromosomes haploid All the DNA in a cell constitutes the cells genome o DNA packaged into molecules called chromosomes o Chromatin a complex of DNA and protein PROKARYOTES o Divide by binary fission splitting into two Duplication of the chromosome cell elongation Movement of origin of replication to opposite ends of the cell actin like proteins may help chromosome move The cell membrane turns inward dividing the cell and new cell wall added in the middle forms septum by FtsZ a tubulin like protein to create two genetically identical cells EUKARYOTES o More DNA complicates cell division o Linear DNA o Chromosome duplicates attached to each other by centromere identical chromosomes called sister chromatids attached by cohesins separation of sister chromatids by separases o Centrosome region that organizes the centrioles and other microtubules MTOC o Kinetochore proteins at centromere that interact with spindle microtubules o Mitotic spindle a structure made of microtubules that controls chromosome movement during mitosis includes centrosome MTs asters Interphase cell growth and copying of chromosomes in preparation for cell division o 90 of cell cycle o G1 phase cell grows o S phase DNA synthesis DNA copied and cell continues to grow o G2 phase cell grows more makes more protiens Mitotic M phase mitosis nucleus division and cytokinesis cytoplasm division o Cytokinesis Animal cell cleavage furrow SEM Contractile ring of microfilaments actin forming a cleavage furrow process called cleavage Plant cell cell plate formation TEM Vesicles derived from Golgi apparatus move to the center coalesce and form cell plate Cytokinesis in plants starts from the inside out G0 phase not dividing Frequency of cell division varies with the type of cell these differences result from regulation at the molecular level Regulation of the cell cycle o Driven by specific chemical signals present in the cytoplasm o Checkpoints border crossing Two types of regulatory proteins Cyclins and Cyclin dependent kinases Cdks Checkpoints also regulated by other internal and external signals Cell fusion experiments indicated that cytoplasmic factors controlled the transitions from one phase to another G1 checkpoint MAJOR CHECKPOINT G2 checkpoint M checkpoint must have full chromosome attachment
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