Mitosis and Cytokinesis Ch 9 The Cell Cycle Mitosis and Cytokinesis

Cell Division In unicellular organisms, division of one cell reproduces the entire organism Multicellular organisms depend on cell division for: Development from a fertilized cell Growth Repair Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division Mitosis Meiosis Binary Fission

Genetic Material Chromosome – coiled DNA – Cell Division Chromatin – uncoiled DNA DNA that is being transcribed – converted to mRNA Chromatid – ½ duplicated chromosome Sister chromatids – same DNA (copies) Centromere – holds chromatids together

Mitosis vs. Meiosis

Mitosis vs. Meiosis Mitosis Meiosis 2 identical daughter cells Somatic cells – body cells Diploid (2n) – 46 chromosomes in humans No variation Copies DNA once – S phase Meiosis 4 non-identical cells Gametes – sex cells Sperm and egg Haploid (n) – 23 chromosomes in humans Variation Crossing over Independent assortment Random fusion of gametes Copies DNA once – S phase

The Cell Cycle Interphase Mitotic Phase: G1: first gap S: growth growth and normal metabolism S: growth metabolism AND chromosome replication G2: second gap growth and prep for mitosis Mitotic Phase: Mitosis: nuclear division Cytokinesis: cytoplasmic division Plant: Cell plate (vesicles from Golgi form new cell wall) Animal: Cleavage furrow (actin and myosin filaments)12_09Cytokinesis_A.swf http://www.biologycorner.com/resources/cell_cycle.jpg

Mitosis pgs. 178-179 Prophase Prometaphase Metaphase (longest) Nucleoli dissappear, mitotic spindle formed, sister chromatids Prometaphase Nuclear envel. Fragments, microtubules invade nuclear area, kinetichore microtubules move chromosomes Metaphase (longest) Centrosomes at opposite sides, chromosomes on metaphase Anaphase (shortest) 12_06Mitosis.mpg Cohesion proteins (holding sister chromatids) cleaved, kinetichore microtubules shorten and pull chromosomes toward opposite ends, cell elongates Telophase Daughter nuclei form, nucleoli reappear, chromosomes become less condensed http://royaleb.files.wordpress.com/2009/04/mitosis_phases1.jpg

Review the structure and function of the cytoskeleton on pgs. 84-86. Fig. 12-7 Aster Centrosome Sister chromatids Microtubules Chromosomes Metaphase plate Kineto- chores Centrosome 1 µm Figure 12.7 The mitotic spindle at metaphase Overlapping nonkinetochore microtubules Kinetochore microtubules Review the structure and function of the cytoskeleton on pgs. 84-86. 0.5 µm

Concept Check What role do motor proteins play in mitosis (pg 180)? What would happen to a cell if a microtubule could not interact properly with tubulin during anaphase?

Binary Fission Prokaryotes and Archea Circular DNA of cell begins to elongate 2 Origins of replication One origin moves to opposite end of cell Cell elongates When replication is complete, the cell divides Yields 2 identical daughter cells http://diverge.hunter.cuny.edu/~weigang/Images/06-11_binaryfission_1.jpg

Internal Regulation of the cell cycle Control system G2 checkpoint M checkpoint G1 checkpoint G1 S G2 M

Cell Cycle Regulation & Checkpoints Stop and go signals G1 “Restriction point” Seems to be most important, if a cell passes it, cell will go through all phases If a cell doesn’t pass G1, it will go to G0 a non-dividing stage. G2 Checkpoint Cdk’s initiates Mitosis M Checkpoint Chromosomes attached to spindle @ metaphase plate = anaphase happens G0 Phase Non dividing, most cells are in this stage

(b) Cell does not receive a go-ahead signal Fig. 12-15 G0 G1 checkpoint Figure 12.15 The G1 checkpoint G1 G1 Cell receives a go-ahead signal (b) Cell does not receive a go-ahead signal

Cyclin dependent kinases – Cdks Not in text Cyclin + Cdks = passage through the checkpoint A kinase that is activated by a cyclin, the Cdk will then phosphorylate an enzyme to cause mitosis to proceed. MPF – cyclin Cdk that promotes mitosis If present mitosis happens If absent mitosis does not happen

Protein kinase activity (– ) Fig. 12-16 RESULTS Notice how cell division follows protein kinase activity 5 30 4 20 3 % of dividing cells (– ) Protein kinase activity (– ) 2 10 1 Figure 12.16 How does the activity of a protein kinase essential for mitosis vary during the cell cycle? 100 200 300 400 500 Time (min)

External Signals that control Cell Cycle Density Dependent Cultured cells normally divide until they form a single layer on the inner surface of the culture container. If a gap is created, cell will fill the gap. Growth Factors proteins released by one group of cells that stimulate other cells to divide. At least 50 different growth factors can trigger specific cells to divide. Anchorage Dependent To divide, they must be anchored to a substratum, typically the extracellular matrix (ECM)of a tissue. Control appears to be mediated by pathways involving plasma membrane proteins and elements of the cytoskeleton linked to them.

Cancer Cells Do not respond to signals of the cell cycle, “trick” the immune system, and cause growth of blood vessels to cancer cells for nutrition. Transformation: a normal cells converts to a cancer cell Benign: abnormal cells remain in one location (rarely cause disease) Malignant: abnormal cells impair functions of one or more organs Metastasis: cancer cells spread to surrounding tissue or throughout body using circulatory system Abnormal Chromosome # http://www.targetedtherapy.info/img/img_cancer_cells.jpg