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Mitosis + Meiosis (Cell Cycle (Nuclear Division Mitosis (Significance,…

- - - - Intensive cell growth + activity
        Produces may cell organelles
        Much protein synthesis
      - Ends with Restriction Point
        Many cells never pass this point
        Cells that pass complete cycle + divide
    - - DNA replicated by semi-conservative method
        Form identical Chromatids joined at Centromere
        Centrioles replicated
    - - Cellular synthesis
        Cell division proteins produced (Eg. Spindle)
        DNA checked + repaired
        Chromosomal material present as Chromatin mass
  - - - Chromosomes condense around histone proteins by spiralisation
        Visible as chromatids joined at the centromere
        Nucleolus disappears
        Centrioles migrate to opposite ends of the cell
        Mitotic spindle forms
        Nuclear membrane disintegrates + disappears
    - - Centromeres attach to equator of spindle
    - - Centromeres split
        Chromatids pulled to opposite poles of the spindle
    - - Chromosomes decondense + uncoil
        Spindle fibres breakdown
        New nuclear membranes form around daughter nuclei
        Nucleolus reappears in each nuclei
    - - Genetic stability
        
        2 daughter cells have exactly the same number of identical chromosomes as parent cell (Genetically identical clones)
      - Growth
        
        New tissue cells carry out the same function as existing ones
      - Repair
        
        Must replace damaged cells with exact copies of original cells for the tissue to function properly
      - Asexual reproduction
        
        Produce offspring genetically identical to parent
      - Mitotic Index
        
        Indication of how much a tissue is actively dividing
        Number of cells in mitosis/total number of cells counted
  - - - Cell membrane begins to reform a cell equator
        Microfilaments pull membrane to form continuous furrow around cell which splits cell
    - - Spindle fibres at the equator persist + bulge outwards to form phragmoplast
        Many cell organelles accumulate
        Golgi produce vesicles which fuse to form cell plate: double membrane later which grows outwards to fuse with membrane
  - - - DNA copies itself by semi-conservative method
        Each copy attaches to cell surface membrane
        Cell elongates, separating copies
        (Same for plasmids)
        Cell membrane invaginates
        New cell wall material laid down forming cross wall
        Daughter cells separated
        Genetically identical cones of each other + parent
    - - Replicate by infecting host cell
        Use it's machinery to produce copy of viral nucleic acid + proteins
        New viral particles assembled
        Released from host cell by bursting cell or budding from host cell membrane
        Exact mechanism depends on type of virus + nucleic acid
      - Examples
        
        Phage + DNA
        
        Injects DNA into bacterial host cell
        Viral DNA copied, transcribed + translated to new viral proteins
        New virus particles assembled + host cell bursts
        
        HIV + RNA
        
        Virus attaches to specific receptor protein on surface of TH cells
        Protein capsid fuses with host cell membrane
        Viral RNA + reverse transcriptase enzyme released into host cell
        Reverse transcriptase makes DNA copy of viral RNA
        Integrated into TH cells own DNA in nucleus
        Transcribed to RNA
        Translated to viral proteins + genetic material of new particles
        Particles assembled + bud off from cell surface membrane
        Take some of membrane with them as lipid envelope
        Infected TH cells do not function normally = compromised immune system
- - - - Chromosomes shorten + condense
        Homologous chromosomes pair up + lie side-by-side to form Bivalent in the process of Synopsis
        Chiasmata exchange genetic material to form new combinations
        Nuclear membrane disappears
        Nucleolus disappears
        Centrioles migrate to opposite poles of the cell
        Spindle forms
    - - Bivalent arranged on equator of spindle
    - - 1 chromosome from each Bivalent pulled to each pole of spindle
        Bivalent act independently of each other so eat pole receives a random mixture of maternal + paternal (independent sortment)
    - - Haploid set of chromosomes at each pole
        Chromosomes decondense
        Nucleoli + nuclear membranes reappear
  - - - Chromosomes condense
        Nucleoli disappear
        Nuclear membranes disintegrate
        Centrioles migrate to opposite poles
        Spindle begins to form
    - - Chromosomes line up on equator of spindle
    - - Centromeres split
        Chromatids pulled to opposite poles of spindle
    - - Chromatids decondense
        Nuclear membranes reform
        Nucleolus reappears
        Spindle breaks down
        Centrioles disappear
  - - - Chiasmata
        
        Genetic material swapped between chromosomes in Bivalent
        Creates new combination of genes + recombinant chromosomes
      - Independent assortment
        
        In meiosis 1 eachbpair of homologous chromosomes acts independently of other pairs when they line up
        New nuclei have random mix of maternal+paternal chromosomes
      - Non-disjunction
        
        Meiosis 1 chromosomes fail to separate
        2 gametes do not have a copy of the chromosome
        2 gametes have an extra copy
        
        Meiosis 2 Chromatids fail to separate
        2 normal gametes
        1 gamete with 1 less chromosome
        1 gamete with 1 more chromosome
        
        Resulting zygote would have an abnormal number of chromosomes