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Chapter 15 - Coggle Diagram

- - - - Cell growth occurs during G1 phase
      - Signaling molecules can cause cell to accumulate molecular changes during G1 that promote progression through the cell cycle
      - If the cell passes the restriction point, or G1 checkpoint, the cell becomes committed to enter S phase and replicate DNA
    - - Chromosomes replicate
      - After replication, two copies stay joined to each other and are called sister chromatids
      - Human cell in G1 has 46 chromosomes
      - Same cell in G2 has 46 pairs of sister chromatids or 92 chromatids total
    - - Cell synthesizes proteins needed during mitosis and cytokinesis
  - - - advancing a cell through the phases of the cell cycle
      - Amount of cyclins varies through cycle
      - Must bind to a cyclin to be active
  - - - DNA replicated
      - Chromatids tightly associated at centromere
      - Serves as attachment site for kinetochore
    - - Ensures that each daughter cell will obtain the correct number and types of chromosomes
      - Mitotic spindle apparatus (or mitotic spindle) is responsible for organizing and sorting the chromosomes during mitosis
      - Composed of microtubules
      - Centrosomes
        
        Microtubule organizing center
        
        Duplicates at the beginning of M phase
        
        Each defines a pole
        
        Only Animal cells have centrioles
      - Spindle microtubules
        
        Astral microtubules – position spindle in cell
        
        Polar microtubules – separate two poles
        
        Kinetochore microtubules – attached to kinetochore bound to centromeres
  - - - Pairs of sister chromatids are aligned along a plane halfway between the poles called the metaphase plate
      - Organized into a single row
    - - Connections broken between sister chromatids
      - Each individual chromatid is linked to only one pole by kinetochore microtubules
      - Kinetochore microtubules shorten, pulling chromosomes toward the pole to which they are attached
      - The two poles move away from each other as overlapping polar microtubules lengthen and push against each other
    - - Nuclear envelope completely fragments
      - Mitotic spindle is fully formed during this phase
      - Centrosomes move apart and demarcate the two poles
      - Spindle fibers interact with sister chromatids
      - Two kinetochores on each pair of sister chromatids are attached to kinetochore microtubules from opposite poles
    - - Chromosomes have reached their respective poles and decondense
      - Nuclear membranes now re-form to produce two separate nuclei
    - - Chromosomes have already replicated and are joined as pairs of sister chromatids
      - Nuclear membrane dissociates into small vesicles
      - Chromatids condense into highly compacted structures that are readily visible by light microscopy
  - - - cleavage furrow
    - - cell plate forms
  - - - Prophase I
        
        chromosomes condense, bivalents form and the nuclear membrane breaks down
      - Prometaphase I
        
        spindle apparatus complete, chromatids attach to kinetochore microtubules
      - Metaphase I
        
        bivalents organized along metaphase plate as double row
      - Anaphase I
        
        segregation of homologues occurs
      - Telophase I
        
        sister chromatids have reached their respective poles and decondense and nuclear membranes reform
      - Cytokinesis
        
        End of meiosis I – two haploid cells
    - - No S phase between meiosis I and meiosis II
      - Sorting events of meiosis II are similar to those of mitosis
      - Sister chromatids separated in anaphase II, unlike anaphase I