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Cell Division (Meiotic Cell Division (Meiosis I (Prophase I (Chromosomes…

- - - - chromosomes become visible
      - homologous chromosomes undergo synapsis
      - pair of homo chromosomes forms bivalent
      - Chromosomes continue to shorten and thicken --> chiasma become apparent
        
        visible manifestation of crossing-over
        
        hold bivalents together during metaphase
      - nuclear envelope begins to break down
    - - spindles attach to both kinetochores in chromosomes
    - - bivalents oriented randomly with respect to each other (independent assortment)
    - - homologous chromosomes separate
      - sister chromatids do not separate
    - - chromosomes do not completely decondense
  - - - cytoplasm divides unequally in both meiotic divisions
      - large cell: oocyte
      - other smaller cells: polar bodies
    - - cytoplasm divides equally
      - functional sperms
  - - - fungi = haploid
      - plants = have both multicellular haploid and diploid phases
- - - - uncontrolled cell division
      - divide on own in absence of growth signals
      - resistance to signals that inhibit cell division or promote cell death
      - metastasis
      - production of signals to promote new blood vessel growth for nutrients to support cell division
- - - - certain sequence of DNA
      - kinetochores attached to region
  - - - Prophase
        
        chromosomes condense --> visible
        
        cells assemble mitotic spindle
        
        centrosome: compact structure
        
        structure from which spindles radiate
        
        During S phase: centrosome duplicates and moves to opposite ends of poles
        
        tubulin dimers assemble around them --> forming microtubules --> mitotic spindle
      - Prometaphase
        
        nuclear envelope breaks down
        
        microtubules of mitotic spindle attach to chromosome
        
        2 protein complexes kinetochores (one located on each side of constriction)
      - Metaphase
        
        chromosomes align in middle of dividing cell
      - Anaphase
        
        centromere holding pair of sister chromatids together splits
        
        spindle microtubules gradually shorten
      - Telophase
        
        microtubules of mitotic spindles break down and disappear
        
        nuclear envelope reforms around each set of chromosomes
        
        chromosomes decondense
    - - contractile ring
        
        ring of actin filaments
        
        ring contracts, pinches cytoplasm
      - Plant cells: phragmoplast
        
        microtubules guide vesicles containing cell wall components to middle of cell
        
        vesicles fuse to create cell plate
  - - - cells pause in cycle
      - Cells still active (carry out metabolism)
    - - specific regulatory proteins made and activated --> promote activity of enzymes that synthesize DNA
    - - size and protein content of cell increase
    - - synthesis of DNA (replication_
- - - - protein assembles and forms a ring at site of constriction
  - - - dinoflagellates (DNA attached to nuclear envelope)
      - mitosis evolved from binary fission
- - - - G1/S cyclin
        
        end of G1 phase
        
        activates protein that promotes expression of histone proteins needed for packaging newly replicated DNA strands
      - S cyclin-CDK complex
        
        necessary for cell to initiate DNA synthesis
        
        prevents synthesizing same sequence
      - M cyclin-CDK complex
        
        phosphorylates structural proteins in nucleus
        
        phosphorylates proteins that regulate assembly of tubulin into microtubules (mitotic spindle)
  - - - DNA damage checkpoint: end of G2 (Is DNA damaged?)
      - DNA replication checkpoint: after G1 (is all DNA replicated?)
      - Spindle assembly checkpoint: before anaphase (are all chromosomes attached to spindle?)