cell cycle and cancer

• Chromosomes

  • long thread-like structure found within the nucleus
  • made up of DNA which carries hereditary information
  • condense into thick, rod-shaped structures when the cell is dividing
• Nucleur envelope:

  separates the contents of the nucleus from the rest of the cytoplasm
• Role of nucleus

  Information is contained within chromosomes which uniquely:

  • control cell activities
  • are copied from cell to cell when cells divide
  • are passed into new individuals when gametes fuse together in sexual reproduction

  The nucleus contains the chromosomes of the cell, and the chromosomes contain the coded instructutions for the organisation and activties of cells and for the whole organism
• structure of chromosomes

  • in non-dividng cells, DNA coils around histone porteins to form long, thin, uncolied threads called chromatin
  • when a cell is preparing to divide (mitosis), the DNA becomes compact, coiled structures called as a crhomosome which i sthe condense state
  • chromosomes hold genes
• features of chromosomes

  1. the shape of a chromosome is charecteristic; they are of fixed length and with a centromere somewhere along their length (which is always in the same position on nay given chromosome)
  2. The number of chromosomes per species is fixed
  3. chromosomes occur in pairs called a homologous pair; one of each pair came originally from each parent
  4. chromosomes are copied (during S-phase), forming 2 identical sister chromatids attached at the centromere till separation
• cancer

  • arises when the cell cycle operates without the normal controls - a molecular control system controlled by sspecific genes
  • rate of cell multiplication is much faster than rate of cell death, and a tumor (ireggular mass of cells) is formed
• Carcinogen

  • any agent that may cause cancer
  • highly likely to cause damage to the DNA molecules, resulting in mutation (a change in the amount of chemical structure of DNA
  • mutations of different types build up in DNA of body cells over time
  • a single mutation is unlikely to be reponsible for triggering cancer
• Ionising radiation

  • includes X-rays and radiation (gamma rays, alpha particals, beta particals)
  • trigger the formation of damaging ions inside the nulceus - leading to the break-up of the DNA
• Non-ionising radiation

  • such as UV light
  • less penetrating than ionising radiation, but if it is absorbed by the the nitrogenous bases of DNA, they may become modified - causing adjecant bases on the DNA strands to bind to each other, instead of binding to their partner on the opposite strand
• Chemicals

  • present in tobacco smoke
  • prolonged exposure to asbestos fibres may trigger cancer in the lining of the thorax cavity (harm only becoms apparent many years later)
• Stages of cancer

  I: A tumor grows from a single cancer cell

  II: Cancer cell invades neighbouring cells

  III: cancer spreads through lymph and blood vessels to other parts of the body

  IV: A small percentage of cancer cells may survive and establish a new tumour in another part of the body
• stages of the cell cycle

  1. Interphase (G1, S, and G2)
  2. Nuclear divison (M)
  3. cell diviosn (cytokinesis)
• G1: the first 'gap' phase


  cell grows by producing proteins and cell organelles, including mitrochondria and endoplasmic reticulum
• Synthesis - phase


  growth of the cell countinues as replication occurs

  protein molecules called histones are synthesized and attached to DNA

  each chromosome becomes 2 sister chromatids
• G2

  cell growth continues by protein and organelle synthesis

  mitochondria and chloroplasts divide

  spindle begins to form