Topic 5 ~ Health, Disease and the Development of Medicines

• Health


  A state of complete physical, mental and social well-being and not merely the absence of disease or infirmity
• Aspects of health


  • Physical
  • Mental
  • Social
• Communicable disease


  Diseases that can be transferred between individuals
• Non-communicable disease


  Diseases that cannot be transferred between individuals
• Presence of one disease can lead to increased susceptibility to other diseases
• Pathogen


  An organism which causes disease
• Types of pathogens


  • Viruses
  • Bacteria
  • Fungi
  • Protists
• Viruses


  • Very small
  • Move into cells and use the biochemistry to make many copies of itself
  • This leads to the cell bursting and releasing all the copies into the bloodstream
  • The damage and destruction of the cells makes the individual feel ill
• Bacteria


  • Small
  • Multiply very quickly through dividing by binary fission
  • Produce toxins that can damage cells
• Fungi


  • Can be single celled or have a body made of hyphae (thread-like structures)
  • Can produce spores which can be spread to other organisms
• Protists


  • Some are parasitic, meaning they use humans and animals as their hosts (live on and inside, causing damage)
• Common infections and their pathogens

  • Cholera (Vibrio cholerae)
  • Tuberculosis (Mycobacterium tuberculosis)
  • Chalara ash dieback (Hymenoscyphus fraxineus)
  • Malaria (Plasmodium falciparum)
  • HIV (Human Immunodeficiency Virus)
  • Helicobacter (Helicobacter pylori)
  • Ebola (B. ebolavirus)
• Methods of pathogen spread

  • Direct contact
  • By water
  • By air
• Damage from disease can be reduced by limiting the spread of pathogens
• Ways to limit pathogen spread

  • Improving hygiene
  • Reducing contact with infected individuals
  • Removing vectors
  • Vaccination
• Lytic pathway of virus lifecycle

  1. Virus replicates its DNA using host cell machinery

  2. Virus particles are assembled

  3. Host cell bursts in lysis

  4. Process repeats with nearby cells
• Lysogenic pathway of virus lifecycle

  1. Virus inserts its DNA into host cell DNA or inserts plasmids into cytoplasm

  2. Host cell replicates, viral DNA is also copied

  3. Lytic cycle begins, starting with assembly of new viral particles
• Sexually transmitted infections (STIs)


  Infections which can be spread through sexual contact
• Examples of STIs


  • Chlamydia
  • HIV
• Spread of STIs can be reduced by using barrier methods of contraception or abstaining from sexual activity
• Plant barriers against disease

  • Physical barriers: Thick cellulose cell wall, Thick waxy cuticle, Layer of bark, Closing of stomata
  • Chemical barriers: Antimicrobial chemicals, proteins and enzymes, Compounds that attract larger insects to feed on pests
• Identifying plant disease in the lab

  1. Take cuttings from diseased plant

  2. Grow pathogen on culture medium/agar plate

  3. Test and identify pathogen using monoclonal antibody testing kit (ELISA)
• Human physical barriers against disease

  • Mucus
  • Cilia
  • Skin
• Human chemical barriers against disease

  • Lysozymes
  • Hydrochloric acid
• Phagocytosis


  White blood cells engulfing and consuming pathogens, destroying them
• Phagocytosis protects by destroying pathogens so they can no longer make you feel ill
• Mucus


  Produced by goblet cells in the airway, traps bacteria and other pathogens before they reach the lungs and cause infection
• Goblet cells in the airway

  • Produce mucus
• Cilia


  • Wafts away mucus that has trapped pathogens, to be killed by stomach acid
• Ciliated epithelial cells


  • Have cilia on their surface
• Chemical barriers


  Provide protection against pathogens
• Skin


  • Provides a physical barrier against pathogens, protecting the tissues and cells beneath it from infection
• Skin cells


  • Provide a physical barrier
• Lysozymes


  Used by white blood cells to kill and digest bacteria
• Hydrochloric acid


  Used to kill bacteria in food reaching the stomach - to prevent infection
• Phagocytosis


  White blood cells engulfing and consuming pathogens
• Producing antibodies


  Each pathogen has an antigen on their surface, which is a structure which a specific complementary antibody can bind to. Once antibodies begin to bind to the pathogen, the pathogens start to clump together, resulting in it being easier for white blood cells to find them and engulf them in phagocytosis.
• Producing antitoxins


  They neutralise the toxins released by the pathogen by binding to them
• Vaccinations


  Involve making an individual immune to a certain disease- they are protected against it before they have been infected
• Herd immunity


  By immunising a large proportion of the population, the spread of the pathogen is reduced as there are less people to catch the disease from