mitosis

• mitosis:

  a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth
• meiosis:

  a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores
• mitosis for growth of multicellular organisms and repair of damaged cells

  miosis part of cell cycle
• cell cycle: the series of events that occur in a cell to produce a new cell

  consists of:

  • cell growth
  • DNA replication- interphase
  • interphase separated into three stages:
  • gap phase 1: cell grows and new organelles and proteins are made
  • synthesis: cell replicates its DNA, ready to divide by mitosis
  • gap phase 2: cell keeps growing and proteins needed for cell division are made
  • mitosis
• mitosis has four stages:

  • prophase
  • metaphase
  • anaphase
  • telophase
• interphase:

  cell carries out normal functions, also prepares to divide

  DNA unravelled and replicated, doubles genetic content

  organelles are also replicated, has spare ones, ATP content increased (ATP provides energy for cell division)
• prophase:

  • chromosomes first become visible, they shorten and thicken
  • tiny bundles of proteins: centrioles start moving to opposite ends of cell, forms network of protein fibres: spindles
  • nucleolus disappear and nuclear envelope break down, releases chromosomes into cytoplasm of cell
  • chromosomes drawn towards equator of cell by spindle fibres attached to centromere
• metaphase:

  • chromosomes are seen to be made up of two chromatids
  • each chromatid has an identical copy of DNA from the parent cell
  • chromatids joined by centromere
  • spindle fibres attach to centromere and arrange on equator of cell
• anaphase:

  • centromere divides, separates sister chromatids
  • spindle fibres pull individual chromatids to opposite poles of spindle
  • moves rapidly and energy provided from mitochondria, which gather around spindle fibre
• telophase & cytokinesis:

  • chromatids reach opposite poles of spindle
  • uncoil, become long and thin, become chromosomes again
  • nuclear envelope form around each group of chromosomes so now two nuclei
  • cytokinesis(starts in anaphase and finishes in telophase) divides cytoplasm
  • forms two daughter cells, genetically identical to original cell and each other
  • mitosis finish and each daughter cell start interphase part of cell for next cycle
• Cancer:

  • mitosis and cell cycle controlled by genes
  • mutation to gene can lead to uncontrolled cell growth
  • uncontrolled cell growth forms group of abnormal cells called tumour
  • cancer is tumour invading surrounding tissue
• maliganant tumours:

  • grow rapidly, less compact and more life threatening
  • cancerous
• benign tumours:

  • grow more slowly, more compact less life threatening
  • non-cancerous
• treatment of cancer:

  • by killing dividing cells by blocking part of cell cycle
  • cell cycle disrupted and cell division, so cancer growth ceases
  • drugs to treat cancer (chemotherapy) disrupts cell cycle by:
  • prevent DNA from replicating
  • inhibit metaphase stage of mitosis interfere with spindle formation
• Investigating mitosis

  1. Cut 2cm from tip from growing root

  2. Prepare boiling tube containing 1M of HCl and put into water bath t 60 degrees

  3. Transfer root tip into boiling tube and incubate for 5 mins

  4. Use pipette to rinse root tip with cold water. Leave tip to dry on paper towel

  5. Place root tip on microscope slide and cut 2mm from very tip of it. Get rid of rest

  6. Use mounted needle break open tip and spread out cells thinly

  7. Add few drops of stain, leave to dry for few mins, stain will make chromosomes to be easily seen under microscope

  8. Place cover slip over cells and push down firmly to squash tissue, makes tissue thinner and allow light to pass

  9. Look at stains through optical microscope
• preparing optical microscope:

  1. clip slide onto prepared stage
  2. select lowest-powered objective lens
  3. use course adjustment knob bring stage to just below objective lens
  4. look down eyepiece, use course adjustment knob to move stage downwards away from objective lens until image roughly in focus
  5. adjust focus with fine adjustment knob, until clear image of slide
• mitotic index calculation:

  mitotic index= (number of cells with visible chromosomes)/ (total number of cell observed)
• measuring cells:

  • using eyepiece graticule and stage micrometer
  • eyepiece graticule: fitted onto eyepiece, transparent with numbers, no units
  • stage micrometer placed onto stage is like microscope slide, accurate scale with units, used to work out value of divisions on eyepiece graticule at particular magnification
• Artefacts:

  • things that can be seen in microscope that are not part of cell or specimen
  • can be dust, air bubbles, and fingerprint, inaccuracies by squashing and staining sample
  • artefacts made during preparation of slides, so need to be careful to not create any artefacts