Cell division

• What are three phases of cell cycle

  interphase

  mitosis

  cytokinesis
• interphase fact sheet 


  during interphase cell increases in mass and size

  has three phases G1 s phase and G2 phase

  in G1 cell gets signal to divide .

  S phase synthesis of new DNA to pro Duce inter chromatids and organelles double

  G2 further cell growth and checking of new synthesised DNA
• what is cytokinesis 


  follow mitosis . whole cell divides and nucleus movs into each cell to creat two genetically identical daughter cells as cytoplasm divides into two.

  in animal cells a cleavage furrow forms and separates daughter cells

  in plants a cell plate(before new cell wall )forms at site of metaphase plate ad once place reaches cell wall of parent cell . New cell walls produced forming new daughter cells
• importance of mitosis 


  growth of multicellular organisms as daughter cells produced genetically identical to parent cell . enables unicellular zygotes to grow into multicellular organisms .

  Replacement of cells and repair of tissue: as cells constantly dying so genetically identical cells produced

  Asexual reproduction of organisms
• Stages of mitosis 


  Prophase

  metaphase

  anaphase

  telophase
• what happens during prophase

  chromosomes condense and become visible

  Sister chromatids joined together at centromere

  centrosomes move to opposite poles and spindle fibres emerge

  nuclear envelope begins to break down
• process of metaphase 


  centrosomes at opposite poles

  chromosomes line up on equator of spindle in middle of cell

  spindle fibres attach to centromeres

  each sister chromatic attach to spindle fibre originating from opposite pole
• process of anaphase 


  sister chromatids separate at centromere as spindle fibres begin to shorten

  separated chromatids pulled to opposite poles by spindle fibres
• process of telophase 


  chromosomes arrive at opposite poles and de condense

  nuclear envelope begins to reform round each set of chromosomes

  spindle fibres break dow
• How to calculate mitotic index 


  mitotic index = number of cells with visible chromosomes/ total number of cells
• cancer fact sheet 


  mutation occurs in genes that control cell division

  cell starts to divide uncontrollably and forms a tumour

  carcinogen are agents that can cause cancer e.g uv light , smoking , X rays

  benign tumours do not spread so don’t cause cancer

  malignant tumours sprea around body destroying other tissues . Cause cancer . Tumour cells can break off and travel via blood or lymph system causing secondary growth (metastasis)

  treatment works by controlling rate of mitosis ,

  methotrexate inhibits DNA nucleotide synthesis

  vincristine and taxol prevent formation of mitosis spindle
• process of binary fission

  single circular DNA molecule undergoes replication

  plasmids undergo replication

  parent cell divides into two cells and cytoplasm halves between two daughter cells

  daughter cell contain single DNA loop and variable number of plasmids

  if daughter cell does not receiveDNA loop or at least one plasmid they die
• how do viruses replicate

  virus attachment protein attaches to cell surface via complimentary receptor proteins

  virus injects DNA or RNA into host cell

  hosT cell then uses nucleic acid and ribosomes to produce new viral particles

  host cell burst and releases new viral particles to repeat cycle