Unit 3 - Infection and Response

• Are viruses living or non-living?

  Non-living
• How do viruses infect the body?

  1. Viruses reproduce rapidly by inserting their genetic material into host cells and creating new protein capsules to build new particles
  2. Once many copies have been made, the host cell may burst open, releasing the viral particles
  3. The viral particles go on to infect other cells
• How can you prevent the spread of tobacco mosaic virus?

  • Separate diseased and healthy plants
  • Good field hygiene and pest control
• Pre-clinical trials

  Pre-clinical trials of the new drug on cells, tissues and live animals to test toxicity, dosage and efficacy
• Clinical trials

  1. Test on healthy volunteers in very low doses to monitor for side effects and safety
  2. Test on infected patients
  3. Optimum dosage trials and test for efficacy
  4. Double blind trial and use of placebo which do not contain the drug
  5. Random allocation of infected patients to groups so no one knows who has the drug
  6. Peer review of data to help prevent false claims
• Making monoclonal antibodies

  1. Take pathogens of disease and inject into mouse
  2. The mouse's immune system is stimulated to recognise the disease and lymphocytes make antibodies
  3. Extract mouse lymphocytes and fuse together with a tumour cell to create a hybridoma
  4. Hybridoma cell divides to form a clone of identical hybridoma cells.
  5. Hybridoma divides rapidly and produces the antibody
  6. A large amount of monoclonal antibodies can be collected and purified
• How does the skin stop pathogens from entering?

  • Tough dry outer layer
  • Skin acts as a barrier
  • Sebum / oil on surface of skin
  • Platelets are involved in forming scabs
• How does the stomach stop pathogens from entering?

  • Contains hydrochloric acid to kill bacteria in food
• How do eyes stop pathogens from entering?

  • Produce tears which contain enzymes to kill bacteria
  • Tears are antiseptic
• How does the breathing system stop pathogens from entering?

  • Trachea and bronchi produce sticky mucus which traps bacteria
  • Mucus carried away by cilia
• Immune system against pathogens

  • White blood cells engulf pathogens
  • White blood cells produce antitoxins which neutralise toxins
  • White blood cells produce antibodies which help destroy pathogens
  • Memory cells are formed, giving a more rapid response if pathogen re-enters
• How do plants defend against microorganisms?

  • CELL WALL, WAXY CUTICLE - tough and difficult to penetrate
  • DEAD CELLS AND DEAD BARK - fall off, taking pathogens with them
  • PRODUCTION OF ANTIBACTERIAL CHEMICALS - kill bacteria
• Measles is a virus spread in droplets when a person coughs or sneezes
• Measles can lead to damage to the breathing system and the brain
• Measles symptoms include a fever and a red skin rash
• HIV

  • The first symptom of HIV is often a flu-like illness.
  • Over time the immune system can become severely damaged, and at some point the patient's immune system becomes so severely damaged that it cannot fight off any other infections that other people could easily deal with.
  • The damaged immune system is unable to fight off cancer cells, and may develop cancer (late stage HIV, AIDS)
• Antiretroviral drugs stop the virus from multiplying inside the patient so the virus does not damage the patient's immune system. Patients who take these drugs do not go on to develop AIDS, so can lead a normal life expectancy, but they must take it for the rest of their lives.
• Gonorrhoea is a sexually transmitted disease caused by bacteria. Symptoms include a thick yellow / green discharge from the penis or vagina as well as pain when urinating.
• People with malaria experience repeated bouts of fever, and it can be fatal.
• Malaria Life Cycle

  1. Infected person is bitten by mosquito
  2. Malaria pathogen passes into mosquito
  3. Mosquito now bites a different person and passes the malaria pathogen to them.
• Ways to prevent spread of malaria

  1. Stop mosquito from breeding - find areas of still water and drain them, or spray areas of still water with insecticides
  2. Prevent mosquitos from biting humans - sleep with mosquito nets, and spray mosquito nets with insecticide
• Antibodies

  • Protein molecules produced by white blood cells
  • Antibodies stick to specific antigens on pathogens, triggering the pathogens to be destroyed
  • Antibodies can remain in the blood for a long time
• Antitoxins are chemicals that stick to toxin molecules and prevent them from damaging cells.
• Rose black spot treatment

  • Fungicides
  • Removing infected leaves and destroy them
• Monoclonal antibodies

  • Are produced from a single clone of hybridoma cells
  • Therefore monoclonal antibodies are specific to one binding site on one protein antigen
  • Therefore monoclonal antibodies can target a specific chemical or specific cells in the body - leads to large number of uses
• A lack of the nitrate ion causes stunted growth as it is required for protein synthesis and therefore growth
• Physical defence systems

  • Cellulose cell walls are difficult for microorganisms to penetrate
  • Waxy cuticle makes it difficult for microorganisms to penetrate
  • Layers of dead cells around stems (bark) act as barriers to entry
• Chemical defence systems

  • Antibacterial chemicals
  • poisons deter herbivores from grazing on plant
• Mechanical defence system

  • Horns or hairs
  • Drooping or curling leaves to scare herbivores
  • Mimicry - white dead nettle looks very similar to stinging nettle but it has no sting
• Monoclonal antibodies for treating cancer

  • Make antibodies specific to cancer cells
  • Attach radioactive substance to antibody
  • When antibody is injected into blood, it attaches to antigens on cancer cells
  • Radioactive substance stops the tumour from dividing, without harming other cells in the body