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• Chromosome


  • DNA
  • Histone protein
  • Sister chromatids
  • Centromere
  • Telomeres
• Mitosis


  • Produces two genetically identical daughter cells for: Growth
  • Cell replacement / tissue repair
  • Asexual reproduction
• Cell cycle


  Regulated cycle of division with intermediate periods of growth
• Stages of the cell cycle

  1. Interphase

  2. Mitosis or meiosis (nuclear division)

  3. Cytokinesis (cytoplasmic division)
• Interphase


  1. G1 - Cell synthesises proteins for replication, cell size doubles

  2. S - DNA replicates, chromosomes consist of two sister chromatids joined at a centromere

  3. G2 - Organelles divide
• Stages of mitosis


  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Prophase


  1. Chromosomes condense and becoming visible, X-shaped, two sister chromatids joined at centromere

  2. Centrioles move to opposite poles of cell (animal cells) and mitotic spindle fibres form

  3. Nuclear envelope and nucleolus break down, chromosomes free in cytoplasm
• Metaphase


  Sister chromatids line up at cell equator attached to the mitotic spindle by their centromeres
• Anaphase


  1. Spindle fibres contract, centromeres divide

  2. Sister chromatids separate into two distinct chromosomes and pulled to opposite poles of the cell (appear as 'V' shapes facing each other)

  3. Spindle fibres break down
• Telophase


  1. Chromosomes decondense and can no longer be observed

  2. New nuclear envelopes form around each set of chromosomes - two new nuclei, each with one copy of each chromosome
• Cytokinesis


  1. Cell membrane cleavage furrow forms

  2. Contractile division of cytoplasm
• Telomeres


  Multiple repeat units of short sequence DNA that cap chromosome tips. The DNA that makes up telomeres is rich in guanine and cytosine.
• Role of telomeres


  • Prevent the progressive loss of DNA in replication
  • The enzyme responsible for replication cannot replicate the full length of the chain
  • Telomeres provide protection against any loss of coding DNA
• Stem cells


  Cells that are unspecialised and retain the ability to differentiate into a range of cell types
• Types of stem cells

  • Totipotent - can develop into any cell type including the placenta and embryo
  • Pluripotent - can develop into any cell type excluding the placenta and embryo
  • Multipotent - can only develop into a few different cell types
  • Unipotent - can only develop into one type of cell
• Where stem cells are found in adult humans

  • Bone marrow
  • Skin
  • Gut
  • Heart
  • Brain
• Uses of stem cells


  • Repair of damaged tissue e.g. cardiomyocytes after myocardial infarction
  • Drug testing on artificially grown tissues
  • Treating neurological diseases e.g. Alzheimer's & Parkinson's
  • Researching developmental biology e.g. formation of organs, embryos
• Specialised cells in blood

  • Erythrocytes (red blood cells) - biconcave and no nucleus to maximise SA for oxygen uptake. Lots of haemoglobin to carry oxygen.
  • Leucocytes (white blood cells) - lymphocytes, eosinophils, neutrophils to engulf foreign material, monocytes.
• How specialised blood cells form

  1. Multipotent stem cells in the bone marrow differentiate into:

  2. Erythrocytes - short lifespan, cannot undergo mitosis as they have no nucleus

  3. Leucocytes, including neutrophils
• Relationship between a system and specialised cells

  Specialised cells → tissues that perform specific function → organs made of several tissue types → organ systems
• Importance of regulating the cell cycle

  Irregular growth of cells where growth or repair is not required can result in the formation of cell masses (tumors). This may lead to cancer.
• Appearance of plant cells at each stage of mitosis


  • Interphase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase