2.8 bio- Disease, Defense and Treatment

• Micro-organisms


  Microscopic organisms that can only be seen under a microscope
• Types of micro-organisms


  • Bacteria
  • Fungi
  • Viruses
  • Protists
• Beneficial micro-organisms


  • Gut bacteria aid in the digestion of food
  • Skin flora compete with pathogens for resources, reducing infection
• Bacteria


  Single-celled organisms that do not have a nucleus or membrane-bound organelles
• Components of bacterial structure

  • Chromosomal DNA
  • Plasmid DNA
  • Cytoplasm
  • Cell wall (made of murein)
  • Cell membrane
• Viruses


  Smaller than bacteria, consisting of a central core of genetic material surrounded by a protein coat, without cytoplasm or cell membrane
• Pathogen


  Disease-causing organism, often a micro-organism such as bacteria, viruses and fungi
• Ways communicable diseases can be transmitted

  • Direct skin-to-skin contact
  • Body fluids (saliva, semen, blood etc.)
  • Drinking contaminated water
  • Eating contaminated food
  • Animal vectors
  • Aerosol infection - airborne pathogens spread by inhaling infected droplets
• Communicable diseases


  • HIV/AIDS
  • Chlamydia
  • Malaria
• Non-specific defence system


  The first line of defence, preventing pathogens from entering the body
• Immune system


  The body's defence against pathogens once they have entered the body, specific to each type of pathogen and aims to prevent or minimise disease
• Types of white blood cells

  • Phagocytes - engulf and digest pathogens
  • Lymphocytes - secrete antibodies and antitoxins
• Antigens


  Molecules on the surface of all cells that are recognised by the immune system, pathogens have unique antigens on their surface
• Antibodies


  Proteins produced by lymphocytes in response to a foreign antigen, each antibody is specific to an antigen and binds to it
• Memory cells


  Lymphocytes that remain in the body after a pathogen has been destroyed, providing immunity if the body is re-infected
• How vaccination works


  1. Dead, weakened or inactivated pathogens are given to the patient

  2. The antigens initiate an immune response resulting in the production of antibodies

  3. Memory cells are produced which remain in the body, providing long-term immunity
• Reasons some parents may choose not to vaccinate their children

  • Concerns about potential side effects/adverse reactions
  • Religious or cultural objections
  • Not guaranteed to work
  • May cause upset to children
  • May believe that vaccines are linked to other diseases such as autism, asthma etc.
• Potential risks and costs associated with not having children vaccinated

  • Risk to the individual child of contracting a potentially life threatening infection (e.g. meningitis)
  • Decrease in 'herd immunity' for that disease in the population, allowing diseases to spread more easily
  • Not all sources of information available are accurate or based on validated, up-to-date science
• Antibiotics


  Substances produced by living organisms that kill or inhibit the growth of bacteria
• Penicillin was the first antibiotic, discovered by Alexander Fleming in 1928
• Due to overprescription and antibiotic misuse, bacteria are becoming increasingly resistant to antibiotics
• Control measures to prevent infection by MRSA

  • New patients screened for MRSA
  • Stringent hygiene measures in hospitals (hospital staff, patients and visitors)
• Control measures to prevent the development of new resistant strains

  • Prescribe antibiotics only when necessary
  • Ensure patients complete their antibiotic courses
  • Variation in the types of antibiotics prescribed
• Drug


  A substance that affects chemical processes within the body
• Preclinical trials for new drugs

  1. Drug tested on cultured human cells and using computer models to determine its toxicity (potential to cause damage) and efficiency

  2. Drug then tested on live animals to establish a safe dose for humans and observe any side effects
• Clinical trials for new drugs

  1. Drug first tested on healthy human volunteers to ensure that it is safe to use and has no other unwanted effects on the body

  2. Drug then tested on patients with the disease to determine its efficacy, dosage is slowly increased until an upper limit is established
• There are risks, benefits and ethical issues associated with the development of new drugs
• Monoclonal antibodies


  Identical antibody clones cultured from one parent lymphocyte cell
• How monoclonal antibodies are produced

  1. Specific antigen injected into an animal e.g. mouse

  2. Lymphocytes producing complementary antibodies extracted

  3. Lymphocytes are fused with myeloma cells to form hybridoma cells, capable of replicating rapidly and producing antibodies

  4. Hybridoma cells cultured

  5. Monoclonal antibodies collected and purified
• Medical uses of monoclonal antibodies

  • Diagnostic tests e.g. for HIV and Chlamydia
  • Tissue typing for transplants
  • Monitoring malaria
  • Cancer treatments