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CELL DIVISION - Coggle Diagram

- - - - primary spermatocyte (2n)
        
        secondary spermatocyte x2 (n)
        
        spermatids x4 (n)
        
        mature sperm cells x4 (n)
  - - - half of chromosomes disposed of in polar bodies after metaphase I and II
      - oocyte meiosis arrests in metaphase II until ferlilisation
      - never completes if unfertilised
    - - maturing oocyte: first meiotic division
        
        secondary oocyte
        
        fertilization
        
        fertilized egg
        
        zygote
        
        second meiotic division
        
        second polar body
        
        first polar body
  - - - homologous chromosomes pair (maternal + paternal)
      - homologous recombination occurs
      - hours in yeast, days in mammals, weeks in plants (massive genomes)
  - - - process called synapsis
  - - - 2^n possible combinations
      - 23 pairs :arrow_right: 2^23 = 8,388,608 combinations
    - - swap large segments of homologous chromosomes
      - creates completely unique chromosomes
    - - non crossing over homologous recombination
      - no chiasmata
        
        method of repairing double stranded breaks
      - copy maternal sequence into paternal chromosome or vice versa
    - - Down syndrome - trisomy (very small chromosome)
      - Trisomy 18 or 13 - usually mosaic (complete trisomies nonviable)
      - Turner syndrome - one X, developmental problems
      - Klinefelter syndrome - XXY (infertility)
      - XYY - no severe symptoms
- - - - Chromosome condensation begins
        
        Cohesion holds sister chromatids together
        
        Condensins: similar ring structure to cohesion, further loop chromatin into tight bundles
        
        Assembly of condensing complexes onto DNA is triggered by the phosphorylation of condenisns by M-CDK
      - Centrosomes move apart, begin to form mitotic spindle
      - Nuclear envelope still intact
    - - condensed chromosomes attach to microtubules
      - nucleus envelope breaks down
        
        phosphorylation of lamina by cyclin B-CDK1 - tetromeres dissociate
        
        fragments form vesicles
        
        vesicles contain lamina B, buut not lammen A/C
        
        nuclear pore complexes (phosphorylated) disassemble
    - - sister chromatids line up on the metaphase plate
        
        equator between two poles
      - Dynamic instability
        
        MTs grow slowly, shrink rapidly
      - physical force from dynamic Mts orients the mitotic spindle
        
        Chromosomes assort in assembly of mitotic spindle - stabilise and organised
      - Kinetochore: protein complex linking chromatin and microtubules
        
        large multimeric complex of structural and signalling proteins
        
        CENP-B protein binds 17bp sequence in centromeric chromatin
        
        sensor proteins that monitor attachment to microtubules
        
        Force of microtubule dynamics pushes/pulls chromatids
        
        balance of forces when aligned on equator
        
        sensor proteins also sense tension
        
        Outer kinetochore
        
        microtubule binding
        
        microtubule motor activity
        
        signal transduction
        
        Inner kinetochore
        
        centromere replication
        
        chromatin interface
        
        kinetochore formation
        
        Inner centromere
        
        chromatid cohesion
        
        passenger proteins
        
        regulation
      - Spindle Assembly Checkpoint
        
        Mitotic Checkpoint Complex (MCC)
        
        inhibits APC when kinetochores are exposed
        
        when all kinetochores attached to spindle
        
        APC released and activated :arrow_right: targets securin (links sister chromatids) for degradation
        
        Separase free to cleave cohesion
        
        Negative feedback loop
        
        just one exposed kinetochore stops APC
        
        signal amplified through kinases
    - - Cohesion degraded
      - sister chromatids move to opposite poles
      - very fast (for cells)
    - - Nuclear envelope reforms
        
        assembles around individual chromosomes
      - microtubules bundle and push nuclei apart
      - contractile ring of actin and myosin begins to form on midline
        
        will become the cleavage furrow
    - - contractile ring cinches and pinches
        
        actin-myosin fibres slide against one another
        
        Starts to assemble just beneath plasma membrane towards end of mitosis
        
        Pulls membrane inwards
      - midbody forms at scission point
        
        can take a long time for cells to completely detach
      - Failure :arrow_right: binucleate cells
      - daughter cells separate
      - Mitotic spindle determines the planes of cytoplasmic cleavage - perpendicular to long axis of mitotic spindle to ensure equal split of chromosomes.
- - - - Replication is completed. Cell prepares to divide
        
        Nucleus breaks apart, and replicated chromosomes condense in preparation for mitosis
        
        Sister chromatids separate during mitosis, and two cells are formed during cytokinesis
        Two daughter cells form, each containing six chromosomes
        
        chromosomal checkpoints
      - lots of synthetic metabolic processes - block to replication
  - - - initiate DNA replication
      - Nuclear envelope breakdown
      - Chromosome separation
    - - Cyclin E - CDK 2 - expression peaks at the beginning of DNA replication (S phase)
      - Cyclin A - CDK 1/2 - expression peaks at boundary between S-phase and G2-phase
      - Cyclin B - CDK1 - expression peaks during mitosis (between prophase and metaphase)
      - Cyclin D - CDK4/6 - expression peaks in G1
    - - adding the small molecule ubiquitin to a protein is the signal for it to be destroyed by the proteosome
  - - - part of the DNA replication complex (sliding clamp)
      - speckled appearance during S phase due to many origins of replication
    - - polarisation of the microtubules into a bipolar spindle
      - process beings in S-phase with duplication of the centrosome - also called the MTOC (microtubule organising centre)
        
        CENTROSOMES
        
        Centrosome
        
        centrioles + mass of proteins called pericentriolar material
        
        Centrioles
        
        comprised of microtubule array
        
        'mother' and 'daughter'
        
        duplicated in S-phase
    - - origins of replication "fire" one per S-phase
        
        cyclin-cdk complexes destroyed by APC/C
      - remove a protein that activates the APC/C, Emi 1
        
        replication origins keep firing
        
        cells never enter M-phase
  - - - one maternal
      - one paternal
    - - 2 copies of replicated chromosome
      - two maternal, two paternal
    - - ESTABLISHMENT OF SISTER CHROMATID COHESION
        
        dsDNA loading (leading strand)
        
        second-ssDNA capture (lagging strand)
        
        stabilisation of second-DNA capture by lagging strand synthesis