16.2 mitosis and cytokinesis

mitosis and cytokenesis

occur in somatic cells

prophase (1 phase of mitosis)

cell has 92 chromatids. chromatin condenses to chromosomes nucleus disappears. centrioles move towards poles of the cell. spindle fibres from spindle apparatus between centrioles

metaphase (2 phase of mitosis)

spindle fibres attach to centromeres (where chromatids connect). sister chromatids are lined along the metaphase plate at the microtubules of the cell. chromatids attach to each centriole by spindle fibres.

anaphase (3 phase of mitosis)

centromeres split. sister chromatids are separate and one moves towards each pole to the cell. microtubules shorten when they attach chromatids to centrioles. other polar microtubules extend. one complete diploid set of 46 chromosomes total is found near each pole

telophase (4 phase of mitosis)

chromatids reach the poles and chromosomes disappear. spindle fibres breakdown, nuclear membrane and nucleus reform. this is the end of mitosis

cytokensis

cytoplasm divides into 2 daughter cells. animal cells: cleavage at the middle of the cell pinches in until cell splits. plant cells: cell membrane forms in middle of cell and eventually divides in 2

regulation of cell cycle

proteins signal when cell division should stop and start. influenced by hormones, nutrients and contact with other cells. cancer is uncontrolled cell growth. cells spend less time in interphase and divide faster results in tumors