BIOMG 1350 1st Edition Lecture 14Outline of Last Lecture I. Cell Division CycleOutline of Current Lecture II. Enter S PhaseIII.Overview of events in M PhaseIV. Mitotic Spindle V. MitosisVI. Bi-orientation of ChromosomesVII. Metaphase AnaphaseVIII. CytokinesisCurrent Lecture- S Phase:o Chromosomal DNA is duplicated; mechanism exist to ensure that it is not over-duplicated each called a chromatid held together at the centromereo Cohesins rings hold the duplicated chromatids togethero Additional: single centrosome is duplicated in preparation for M phaseo If everything is ok, it goes right to M phase- M Phase:o Two distinct overlapping parts: The equal segregation of the duplicated chromosomes by the microtubule-based mitotic spindle MITOSIS The division of the cytoplasm in two halves to generate two cells by contraction of the microfilament based contractile ring  CYTOKINESIS Different in plantso Interphase (not part of M phase)o Prophase centrosome move to opposite ends, Prometaphase nuclear envelope breaks, capture of chromosomes by microtubules Metaphase: chromosome lined up and attached checkpoint: are they attached?  Anaphase: pull apart Telophase  Cytokinesis- Mitotic Spindle:o Review microtubules:o Kinetochore links microtubules to centrosomeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Cohesins hold chromatids togethero 1 chromosome= 2 chromatidso Three distinct classes of microtubules: Aster come out of spindle pole and go to cell (+) end Kinetochore connect to centrosome Interpolar interconnected- Mitosis:o Interphase: Chromosomes duplicated, held together by centrosome Centromere duplicatedo Prophase: breakdown of interphase microtubules and its replacement by aster Mitotic aster separation Chromosome condensation  Kinetochore assembled on chromosome (where poles of microtubules attach)o Prometaphase: Nuclear envelope breakdown give m.t. access to chromosomes Chromosomes captured and bi-oriented and brought to spindle equatoro Metaphase: Chromosomes line at metaphase plate- Bi-orientation of Chromosomes:o Microtubules captured by kinetochoreso Unattached chromosome at prometaphase unipolar attachment; m.t is called kinetochore m.t chromosome orientated so m.t from opposite spindle pole to convert unipolar to bipolaro Tension creates a stable bi-polar attachmento Aurora B kinase: phosphorylation/ dephosphorylation of kinetochore components tension causes stable m.t attachment kinetochore components dephosphorylatedo Checkpoint is satisfied activates APC degradation of m-cyclingo APC: normally inactive When checkpoint is satisfied it is activated Put ubiquitin and degradation of M-cyclin inactive m-CDK Cleavage of cohesion Securin (inhibitory protein) ubiquitlated by APC and degrades leads to active separase and dissociates cohesins- Metaphase Anaphase:o Anaphase A: chromosomes are pulled poleward, kinetochores m.t become shorter Forces are generated at kinetochores to move chromosomes towards their spindle poles M.T is stimulated to disassemble on its plus end Forces washer to go down M.T (pulling force) (MT depolymerization)o Anaphase B: at same time, poles are pushed and pulled apart Interpolar M/T from opposite poles to push the poles apart; pulling force Acts directly on the pole to move them apart On aster m.t., dyenin (towards - end) pulls on aster M.T> and elongates the spindle- Cytokinesis:o Telophase: Nuclear envelope reassembleso Cytokinesis: contractile ring of actin and myosin forms 2 cells and forms cleavage furrow In plant cells: don’t contract, they lay down plate and lay down a cell