Cell Cycle: Mitosis

Cell Cycle: Mitosis

1. need to reproduce: grow, replicate, segregate chroms to daughter cell

2. Don't replicate while seg.= then wrong # of chroms

   • Don't seg while replicating=trying to seg 2 copies that arent there yet

3. WHY USE Fission Yeast: cells can replicate quickly, small, cheap, easy to tell what stage it is, they can be hapliod

   • Haploid: they only have single copy of each gene; introduce random mutation into genome & its more straight forward to see effects

4. Inhibit transition to division; find mutant that gets to big b4 it divides, by adding random variables to genome

   • Genetic screen (for bio Qs)use a model system like yeast and introduce random genes into the genome, ask what mutants you can find
     • Found cells that were too small (Wee Mutants)
       • He isolated 6 mutants w/ wee mutants; 5 were mutants of the same gene called Wee 1
         • Is there an equalivalent mutant in human cell like Cdc2
           • Human gene can restore the function (?)

5. Xenopus (Frog) oocytes goes through meiosis to make an egg

   • arrested in G2 phase and need a signal to transition
     • take cyoplasm from cells that are arrested in mitoic phase, and adds it to the other one, the other one divides
       • MPF (Maturation-Promoting Factor): stimulates division
         • inject it into oogocyte
           • any cell in dividing stage has high MPF in cytoplasm: you could take it and induce division in other cells

6. Look for patterens of protein sythensis

   • Hunt anzlyed protein sythesis
     • as cells divide levels of cyclin go down
       • Cyclyin-dep kinase (CDK) when u have cyclin CDK is active
         • Ubiquiitin mediates protein degridation
           • attaches to protein & brings sit to proteasome
             • uiquitalation is irreversible

7. Chromosomes& tansiton

   • Checkpoints control transition: finish one thing bc you can't go back
     • G2/M: influenced by cell size and DNA damage & replication
       • NEED: ubiquitin mediated regulation of cyclin: degredation of cyclin
     • Regulate Cyclin protein: Cyclin levels high
     • Restriction Point: turn on CDC 25
       • Regulation by phopsphorlation
   • After cells replicate in S phase they are held together by cohesion protein: it forms a bond on the chromosome

8. Prophase: condense chromosome,centrosomes have replicated from interphase (like the DNA) and they move

   • Centromere: special reason, to build the kinetichore
     • Kinetichore allows us to bind microtubles
   • The arms of the chromosome contain the genetic info but dont do anything
   • Prometaphase: nuclear envelope broken up: typical of animal cells
     • Centrosome on opp sides, Mitotic Spindle (pull chromosomes apart)
       • Microtubles grab chromosomes kinetichores
         • All chromosomes need to be attached to microtuble or else they wont divide properly in anaphase and get daughter cells with wrong chromosomes or wrong number of chrosomes
     • Metaphase
       • Anaphase: seperation
         • Remove the cohesin protein and then they are pulled off
           • Anaphase is the irreversible point of the dividion bc the cohesin can't be put back on
             • As the microtubles shorten they pull, part of dynamic nature
               • Source of energy that moves chromosome= GTP bc when monomer r incorporated into polymer the GTP is hydrolyzed , storing energy in the conformation
               • Depolymerization of the + end pulls the chrosomes
         • Telophase: Contractile Ring uses actin to make a ring around the middle
           • Cytokenisis the cell is cleaved
         • Anaphase promoting complex: ubiquitin ligase= enzye that leads to ubiquitlzation of cyclin which turns off CDK degrades securin
         • Is irreversible because (key proteins) cyclin and securin r degraded by complex
       • EVery pair of chromosomes one attaches to a micrutubles through
         • Need to get a correct alignment of chromosomes HERE
       • Seperase= Protease (cleaves off proteins (spec. cohesin); cuts off cohesin ring
       • Turn of CDK: Cyclin gets deraded by ubiqilatin, lose CDK
       • Securin: keeps seperase inactive; it is also ubiquitlated by anaphase promoting complex and degraded allowing seperase to be
       • Every chromosome is attached to a microtuble, where one is pulling in one direction

9. ALL chromosome NEED to be captured by microtubles, or else it can't be segrated in anaphase bc it wont get pulled; this messed up segration

   • Dynamic microtobles (+ ends are dynamic): grow and shrink to search whole cyoplasm to capture a kinetochore and then the dynamics stop (thats what kinetochore does)

10. As cells leave mitosis

    • 1. separation of chromo: remove cohesion& turn off cyclin dep kinase
      • Dephosphorlation turns of mitosis
    • Increase activity ishow cells go into M phase