1.6: Cell division
Mitosis Defined as: division of a nucleus into two genetically identical daughter nuclei. When does mitosis occur? Growth (incl. embryonic development) Repair Asexual reproduction
I P M A T C interphase prophase metaphase anaphase telophase cytokenesis
Before… DNA is replicated, cell makes a complete copy of it’s genetic material (Interphase). Each chromatid has an identical copy (sister chromatid) Sister chromatids are attached at the centromere
Prophase Chromosome become visible – shorter & coil Homologous chromosomes (homologues) pair up – maternal & paternal chromosomes are side by side (their formation is known as synapsis) Spindle fibers made from microtubules form.
Metaphase Bivalents (paired homologous chromosomes) line up along equator Nuclear membrane disappears Spindle attaches to centromere
Anaphase Spindle fibers from poles attach to chromosomes Spindle fibers pull chromosomes to the poles of the cell Sister chromatids separate.
Telophase Spindles & spindle fibers disintegrate Chromosomes uncoil Nuclear membrane forms Two genetically identical daughter cells are formed.
Task: Make a mitosis ‘flip book’ detailing the stages of mitotic division. Notes available on pg. 53/54.
Mitotic index = number of cells in mitosis The mitotic index Using a micrograph to estimate the ration between the number of cells in mitosis and the total number of observed cells. Mitotic index = number of cells in mitosis total number of cells
Cytokinesis Is different in plants and animals. Plants Animals Vesicles move to the equator, fusing together forming a double plasma membrane layer across the cell. Pectin & other substances are moved between this new layer, combining with cellulose to eventually form a new cell wall. Plasma membrane pulled inwards Proteins actin & myosin contract the plasma membrane, pinching the cell into two.
The Cell Cycle Regulated by cyclins (proteins). Cyclins bind to enzymes called cyclin- dependent kinases Active kinase attach phosphate groups to other proteins which triggers more proteins to become active. In humans there are four types of cyclin. See fig. 6, pg. 56
Tumours & cancer Read detail on pg. 57, including the correlation between smoking and cancer. Data based qu. Pg. 59.