All cells arise from other cells

• State what the cell cycle is and outline its stages

  ~Cycle of division with intermediate growth periods

  ~Interphase

  ~Mitosis or meiosis

  ~Cytokinesis
• Explain why the cell cycle does not occur in some cells

  After differentiation, some types of cell in multicellular organisms no longer have the ability to divide
• What is the difference between the cell cycle and mitosis

  ~Cell cycle includes growth period between divisions

  ~Mitosis is only 10% of the cycle and refers only to nuclear division
• Outline what happens during interphase

  G1: Cell synthesises proteins for replication e.g. tubulin for spindle fibres and cell size doubles

  S: DNA replicates = chromosomes consist of two sister chromatids joined at a centromere

  G2: Organelles divide
• State the purpose of mitosis

  ~Produces two genetically identical daughter cells

  ~Growth

  ~Cell replacement/ tissue repair

  ~Asexual reproduction
• Name the stages of mitosis

  ~Prophase

  ~Metaphase

  ~Anaphase

  ~Telophase
• Outline what happens during prophase

  ~Chromosomes condense, becoming visible.

  ~Centrioles move to opposite poles of cell and mitotic spindle fibres form

  ~Nuclear envelope and nucleolus break down = chromosomes free in cytoplasm
• Outline what happens during metaphase

  Sister chromatids line up at cell equator, attached to the mitotic spindle by their centromeres
• Outline what happens during anaphase

  ~Spindle fibres contract = centromeres divide

  ~Sister chromatids separate into two distinct chromosomes and are pulled to opposite poles of cell

  ~Spindle fibres break down
• Outline what happens during telophase

  ~Chromosomes decondense, becoming invisible again

  ~New nuclear envelopes form around each set of chromosomes = two new nuclei, each with one copy of each chromosome
• Explain the procedure for a root tip squash experiment

  ~Prepare a temporary mount of root tissue

  ~Focus an optical microscope on the slide. Count total number of cells in the field of view and number of cells in a stage of mitosis

  ~Calculate mitotic index
• Explain how to prepare a temporary root tip mount

  ~Place root in hydrochloric acid to halt cell division and hydrolyse middle lamella

  ~Stain root tip with a dye that binds to chromosomes

  ~Macerate tissue in water using mounted needle

  ~Use mounted needle at 45° to press down coverslip and obtain a single layer of cells. Avoid trapping air bubbles
• Name two dyes that bind to chromosomes

  ~Toluidine blue (blue)

  ~Acetic orcein (purple-red)
• Why is only the root tip used when calculating a mitotic index

  ~Meristematic cells at root tip are actively undergoing mitosis

  ~Cells further from root tip are elongating rather than dividing
• What are tumour suppressor genes


  Genes that code for proteins to trigger apoptosis
• What are proto-oncogenes


  Genes that code for proteins to stimulate cell cycle to progress from one stage to the next
• How can mutation to tumour suppressor genes and proto-oncogenes cause cancer

  ~Tumour suppressor: no production of a protein needed to slow the cell cycle

  ~Proto-oncogenes: form permanently activated oncogenes

  ~Disruption to cell cycle - uncontrolled cell division - tumour
• Suggest how cancer treatments control the rate of cell division

  ~Disrupt cell cycle

  ~Prevent DNA replication

  ~Disrupt spindle formation = inhibit metaphase/anaphase

  ~Can also damage healthy cells
• How do prokaryotic cells replicate

  ~DNA loop replicates. Both copies stay attached to cell membrane. Plasmids replicate in cytoplasm

  ~Cell elongates, separating the two DNA loops

  ~Cell membrane contracts and septum forms

  ~Cell splits into two identical progeny cells, each with one copy of the DNA loop but a variable number of plasmids
• Why are viruses classified as non-living

  ~They are acellular

  ~No cytoplasm

  ~Cannot self-replicate
• Outline how viruses replicate

  ~Attachment proteins attach to receptors on host cell membrane

  ~Enveloped viruses fuse with cell membrane or move via endocytosis and release DNA/RNA into cytoplasm or viruses inject DNA/RNA

  ~Host cell uses viral genetic information to synthesise new viral proteins/nucleic acid

  ~Components of new viral particle assemble
• How do new viral particles leave the host cell

  ~Bud off and use cell membrane to form envelope

  ~Cause lysis of host cell
• Why is it so difficult to develop effective treatments against viruses

  Replicate inside living cells = difficult to kill them without killing host cells