Mitosis & Cancer

• MITOSIS CELL DIVISION:

  • THE CELL CYCLE: Cells go through a series of times and regulated stages of growth, DNA replication, and division (the cell cycle)
  • PURPOSE OF THE CELL CYCLE: New cells are needed to replace worn out/ damaged ones. To help organisms grow. 
  • PHASES OF THE CELL CYCLE: 2 major phases: interphase (the cell grows and DNA is replicated) & the mitotic phase (the replicated DNA and cytoplasmic contents are separated & the cell divides). 2 types of division in eukaryotes: mitosis and meiosis.
• MITOSIS CELL DIVISION:

  -INTERPHASE: is subdivided into growth stages G1, S and G2 stage. G1= the cell grows. S= DNA synthesis happens. G2= cell grows more before the mitotic phase.

  -THE MITOTIC PHASE: mitosis is part of the cell cycle where a eukaryotic cell divides to produce 2 daughter cells, each with identical copies of DNA (produced from the parent cell during replication). Multicellular organisms go through mitosis to grow & repair damaged tissues
• STAGES OF MITOSIS:

  1)INTERPHASE: The cell prepares to divide by replicating DNA by semi-conservative replication (there are 2 copies of every chromosome). The organelles are also replicated, and more ATP is produced to be used in cell division.
• STAGES OF MITOSIS:

  2) PROPHASE: The nuclear envelope breaks down and the nucleolus disappears so chromosomes are left floating in the cytoplasm. The chromosomes coil more tightly and become shorter & fatter. They can be seen under a light microscope. Centrioles (small protein bundles) move to opposite poles of the cell. Microtubules form the mitotic spindle between the centrioles
• STAGES OF MITOSIS:

  3) METAPHASE: The chromosomes line up along the middle of the cell. In metaphase the chromosomes are maximally condensed. They are attached to the spindle by the centromere
• STAGES OF MITOSIS:

  4) ANAPHASE: The chromosomes break into 2 chromatids and the sister chromatids separate at the centromere. The spindles contract and pull the chromatids to each pole of the cell
• STAGES OF MITOSIS:

  5) TELOPHASE: The chromatids reach opposite poles and begin to decondense & unravel, becoming chromosomes again. Nuclear envelopes form around the chromosomes so there are now 2 nuclei. The cytoplasm splits and 2 daughter cells are formed that are identical to the parent cell and each other. The cell cycle repeats.
• ACRONYM FOR MITOSIS:

  • I: (interphase)
  • PICKED: (prophase)
  • MY: (metaphase)
  • APPLES: (anaphase)
  • TODAY: (telophase)
• STAINED SQUASHES OF CELLS (FROM ROOT TIPS)

  1. PREPARATION: Root tips (actively growing) put into 5M hydrochloric acid, after 5 mins, rinsed in cold water
  2. CUT THE TIPS: to 2mm long. Place a tip on a clean microscope slide, to reduce artefacts.
  3. STAINING: Add 2-3 drops of stain, leave for 2 mins. Spread the tips into a thin layer and place a coverslip over it.
  4. SQUASHING: by applying force to the cover slip, vertical or the cover slip might break & cause injury.
  5. VIEWING: Cells closer to the tip will be ones more actively dividing. Chromosomes should be able to be seen
• THE MITOTIC INDEX:

  • EQUATION: Mitotic Index= Number of cells in mitosis/ total number of cells
• BINARY FISSION:

  1. The circular DNA molecule replicates and both copies attach to the cell membrane
  2. The plasmids also replicate
  3. The cell membrane begins to grow between the 2 DNA molecules and begin to pinch inward, dividing the cytoplasm in 2
  4. A new cell wall forms between the 2 molecules of DNA, dividing the original cell into 2 identical daughter cells, each with a single copy of the circular DNA and a variable number of copies of the plasmids
• CELL SIZE:

  • CALCULATING CELL SIZE: Eyepiece graticule= glass disc in eyepiece of a microscope. Cells can be seen through a microscope and a micrometre used to calculate the actual size of them.
  • CALIBRATING EYEPIECE GRATICULE: The eyepiece graticule must be calibrated to calculate cell size and its calibrated by comparing the length of each division to that of a micrometre.
  • CALCULATING ACTUAL CELL SIZE: Actual size= image size/ magnification
• CANCER:

  • GENE MUTATIONS: The cell cycle is tightly controlled by genes, however errors can still occur. Changes to the DNA nucleotide sequence -> (can cause) a gene mutation -> (may cause) a faulty protein. A change in the cell resulting from the malformed protein -> (may allow) mistakes to happen more often
  • UNCONTROLLED CELL DIVISION: Small uncorrected errors are passed from the parent to the daughter cells . As each generation produces more non - functional proteins, mutations can accumulate -> (can lead to) uncontrolled growth of mutated cells -> a tumour is formed
• CANCER TREATMENT:

  • G1: A phase in interphase that produces new organelles & causes the cell to grow. If the genes that encode new enzymes are mutated -> cell cycle can be altered. Drugs can inhibit G1 & treat cancerous cells (the drugs halt the cell cycle and kill the cells)
  • S PHASE: A stage in interphase that causes DNA to replicate. Errors in DNA replication -> (could lead to) tumours. Drugs can be used to target the DNA and kill the cells (to prevent the spread of a tumour)