Cellular Division:Cellular Division:

MitosisMitosis

((Text Ch. 10, pp. 240-248Text Ch. 10, pp. 240-248))

Reasons for Cell divisionReasons for Cell division

Basis of reproduction for all cellular organismsBasis of reproduction for all cellular organisms Enables multicellular organisms to growEnables multicellular organisms to grow Replaces worn-out or damaged cells and Replaces worn-out or damaged cells and

tissuetissue

““Analysing Data”, p. 249Analysing Data”, p. 249

Life Span of Human CellsLife Span of Human Cells– 1. White blood cells: function vs lifespan1. White blood cells: function vs lifespan– 2. Consequences of injury to heart + spinal cord? Smooth 2. Consequences of injury to heart + spinal cord? Smooth

muscle?muscle?– 3. Hypothesis for data 3. Hypothesis for data – 4. Cancer: predict data table4. Cancer: predict data table

Summary of Cell divisionSummary of Cell division

Prior to division, cell replicates all of Prior to division, cell replicates all of its DNAits DNA– One complete copy will go to each One complete copy will go to each

“daughter” cell“daughter” cell

Recall:Recall:

genetic info for eukaryotic cells is genetic info for eukaryotic cells is contained in a contained in a membrane-bound membrane-bound nucleusnucleus

Before the cell can divide, the Before the cell can divide, the nucleus must also dividenucleus must also divide

Recall:Recall:

Two types of cell division:Two types of cell division:– 1. Mitotic1. Mitotic

46 46 doubledouble 46 46 singlesingle chromosomes chromosomesAsexual, body cellsAsexual, body cells

– 2. 2. Meiotic Meiotic 46 double46 double 23 single23 single chromosomes chromosomesSexual cellsSexual cells

Two Main Stages of Cell DivisionTwo Main Stages of Cell Division

1. Mitosis1. Mitosis::– division of the nucleus division of the nucleus – formsforms 2 daughter nuclei 2 daughter nuclei – each has aeach has a full, identical chromosome full, identical chromosome

set set 2. Cytokinesis2. Cytokinesis: :

– division of the cytoplasmdivision of the cytoplasm b/w 2 daughter b/w 2 daughter cellscells

Cell CycleCell Cycle

Interphase ~ Interphase ~ 90% of time90% of time

Mitotic phase Mitotic phase ~10% of time~10% of time

Nucleus contains DNA and proteinsNucleus contains DNA and proteins DNA packed tightly into DNA packed tightly into chromatinchromatin fibres fibres

Chromatin:Chromatin:– DNA coiled around DNA coiled around histone moleculeshistone molecules (protein) (protein)– Coils are then coiled into long fibres Coils are then coiled into long fibres

Fibres dispersed throughout nucleusFibres dispersed throughout nucleus

Chromosome StructureChromosome Structure

Fig. 12-10, p. 297

Chromosome Formation during Chromosome Formation during MitosisMitosis

Chromatin fibres gather + coilChromatin fibres gather + coil Bunched into compact Bunched into compact chromosomeschromosomes Set # of chromosomes per sp.Set # of chromosomes per sp.

InterphaseInterphase Cell growth (G1)Cell growth (G1)

DNA synthesis (S)DNA synthesis (S)– Chromosomes Chromosomes

duplicate, still loosely duplicate, still loosely packedpacked

Produces proteins + Produces proteins + organelles for div. organelles for div. (G2)(G2)

ProphaseProphase

Chromatin fibres Chromatin fibres condense into condense into chromosomeschromosomes– two “sister” two “sister”

chromatidschromatids– attached at a attached at a

narrow waist narrow waist ((centromerecentromere))

Spindles formSpindles form

Prophase, cont’dProphase, cont’d

Centrioles at polesCentrioles at poles

Spindles grow, reach Spindles grow, reach chromosomeschromosomes

Nuclear envelope Nuclear envelope breaks down & breaks down & disappearsdisappears

MetaphaseMetaphase

Chromosomes line Chromosomes line up along metaphase up along metaphase plate at centreplate at centre

Each Each chromatidchromatid connected at connected at centromere to a centromere to a spindle fibre from spindle fibre from each poleeach pole

AnaphaseAnaphase

Centromeres split Centromeres split as spindle fibres as spindle fibres pull chromatids pull chromatids apartapart

Form group of Form group of single single chromosomes chromosomes at at each poleeach pole

Cell elongation Cell elongation beginsbegins

TelophaseTelophase

Cells elongateCells elongate

Daughter nuclei Daughter nuclei appear at each pole appear at each pole as envelope re-formsas envelope re-forms

Chromatin fibres Chromatin fibres uncoiluncoil

Telophase and CytokinesisTelophase and Cytokinesis

Cleavage furrow (animal)Cleavage furrow (animal)– Cell plate (plant)Cell plate (plant)

Cells contain ½ the cytoplasm, but same Cells contain ½ the cytoplasm, but same # chromosomes as parent cell# chromosomes as parent cell

Mitosis in action:Mitosis in action:

http://www.teachersdomain.org/resohttp://www.teachersdomain.org/resource/tdc02.sci.life.stru.dnadivide/ urce/tdc02.sci.life.stru.dnadivide/

““Go Online” (p. 245 text)Go Online” (p. 245 text)

Controls on Cell DivisionControls on Cell Division

Cell activity controlled by proteins Cell activity controlled by proteins (e.g. cyclins) and other regulators (e.g. cyclins) and other regulators – E.g. healing a cutE.g. healing a cut

What might happen without controls?What might happen without controls?– E.g. Cancer – how does it work?E.g. Cancer – how does it work?– http://http://www.youtube.com/watch?vwww.youtube.com/watch?v

=dK9UcjSPkLs&feature=related=dK9UcjSPkLs&feature=related