All Cells Arise From Other Cells

• What happens in interphase?

  • S phase: DNA replicates semi-conservatively
  • leading to 2 chromatids joined at the centromere
  • G1/G2 number of organelles and the volume of cytoplasm increases, protein synthesis
• G1 Phase: Cell grows, proteins are synthesised
• G0 Phase: Cell is not dividing but can enter G1 again if stimulated by growth factors.
• What happens in mitosis?

  nucleus divides to produce 2 nuclei with identical copies of DNA produced by parent cell
• What happens in cytokinesis?

  cytoplasm and cell membrane divide to form 2 new genetically identical daughter cells
• What happens in prophase?

  Chromosomes condense, becoming shorter and thicker (visible), appear as 2 sister chromatids joined by a centromere; nuclear envelope breaks down; centrioles move to opposite poles forming spindle networks

  
• What happens in metaphase?

  spindle fibres attach to chromosomes by their centromeres; chromosomes align along equator

  
• What happens in anaphase?

  spindle fibres shorten and contract; centromere divides, pulling chromatids from each pair to opposite poles of the cell

  
• What happens in telophase?

  Chromosomes uncoil, becoming longer/thinner; nuclear envelopes reform (2 distinct nuclei); spindle fibres/centrioles break down

  
• Why do some eukaryotic cells not undergo the cell cycle?

  not all cells retain the ability to divide (e.g neurons)
• Explain the importance of mitosis in the life of an organism


  parent cell divides to produce 2 genetically identical daughter cells for growth of multicellular organisms by increasing cell number, replacing cells to repair damaged tissues, asexual reproduction
• Describe how tumours and cancers form

  mutations in DNA controlling mitosis can lead to uncontrolled cell division, tumour formed if this results in mass of abnormal cells
• Suggest how cancer treatments control rate of cell division

  some disrupt spindle fibre activity (so anaphase can't happen); some prevent DNA replication during interphase
• Describe how prokaryotic cells replicate

  replication of circular DNA, replication of plasmids, division of cytoplasm to produce 2 daughter cells (single copy of circular DNA, variable number of plasmids)
• Describe how prokaryotic cells replicate


  replication of circular DNA, replication of plasmids, division of cytoplasm to produce 2 daughter cells (single copy of circular DNA, variable number of plasmids)
• Describe how prokaryotic cells replicate

  replication of circular DNA, replication of plasmids, division of cytoplasm to produce 2 daughter cells (single copy of circular DNA, variable number of plasmids)
• Describe how viruses replicate

  Attachment proteins attach to complementary receptors on the host cell, inject viral nucleic acid into the host cell, Infected host cell replicates virus particles (nucleic acid replicated, cell produces viral protein/capsid/enzymes, virus assembled and released)