All Cells Arise From Other Cells

• Outline the differences between mitosis and meiosis.

  • Mitosis results in 2 genetically identical diploid daughter cells
  • Meiosis results in 4 genetically different haploid daughter cells.
• List stages of mitosis

  • Interphase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Outline Interphase

  1. Cells not dividing
  2. replication of DNA - two copies on centromere
• Outline prophase

  1. Chromosome become more visible and thicken
  2. Centrioles move to opposite ends of the cell (poles)
  3. spindle fibres develop from each of the centrioles
  4. Nucleolus disappears and the nuclear envelope breaks down, leaving the chromosomes free in cell cytoplasm
• Outline metaphase

  1. Chromosomes seen to be made up of two chromatids
  2. chromosomes pulled to the cell equator where they line up
• Outline anaphase

  1.  Centromeres divide, separating each pair of sister chromatids
  2.  Chromatids pulled to their respective poles as spindles contract
• Outline telophase

  1. Chromosomes reach their respective poles and then uncoil, become long and thin again - chromosomes again
  2. Spindle fibres disintegrate; nuclear envelope and nucleolus reform
  3. Cytoplasm divides in cytokinesis
• Outline the process of Binary Fission

  1. Circular DNA molecule replicates, and both copies attach to the cell membrane
  2. Plasmids also replicate
  3. Cell membrane begins to grow between the two DNA molecules and begins to pinch inwards - dividing cytoplasm in two
  4. New cell wall forms between the DNA molecules, dividing the original cell into two identical daughter cells - each with a copy of the circular DNA and a variable number of copies of the plasmids
• Outline how viruses replicate

  1. HIV Attachment proteins attach to receptors on helper T lymphocytes
  2. HIV RNA enters the cell
  3. Reverse transcriptase converts RNA to DNA
  4. Viral capsid and enzymes produced
  5. Virus assembled and released
• Why is mitosis so important

  1. Growth - ensures that all cells growing from original cell of an organism are genetically identical.
  2. Repair - Important that replacement cells produced have an identical structure and function to lost cells
  3. Reproduction - Single-celled organisms divide by mitosis to give 2 new organisms - each new organism is genetically identical to the parent organism
• Mitotic Index - equation

  number of cells undergoing mitosis (cells with visible chromosomes) / total number of cells in field of view
• Outline the stages of the cell cycle

  1. G1 - cell grows, new organelles and proteins made
  2. S - synthesis - DNA replication
  3. G2 - cell keeps growing and proteins needed for cell division are made
  4. Mitosis
  5. Cytokinesis
• Difference between benign and malignant

  Malignant - grow rapidly, less compact, more likely to be life-threatening

  Benign - grow more slowly, more compact, less likely to be life-threatening.
• How can cancer be treated?

  • Involves killing dividing cells by blocking a part of the cell cycle - cell division and therefore cancer growth ceases.
  • Chemo disrupts cell cycle by preventing DNA replication or by inhibiting the metaphase stage of mitosis by interfering with spindle formation.