Higher Biology

1. Higher Biology Cellular Defence Mr G Davidson

2. Cellular Response • Both animals and plants have mechanisms to defend themselves against disease. • Some operate at the level of the whole organism i.e. a tough outer skin or epidermis. • Others operate at a cellular level. G Davidson

3. Viruses • Viruses are micro-organisms which can only be seen with the aid of an electron microscope. • They consist of a protein coat surrounding a core of nucleic acid. G Davidson

4. Viruses • Viruses are incapable of independent respiration but can reproduce within a living host cell. • They form one of the important groups of disease causing agents. • Since they can only survive in a host they are said to be obligate parasites, and the host cell is usually destroyed. G Davidson

5. Viruses • Viruses can be transmitted in a number of ways, e.g.: • by blood and sexual fluids e.g. HIV • from faeces and passed to food by insects e.g. polio • by coughing and sneezing e.g. flu and pneumonia. • by contact e.ge.g. cold sores flu and pneumonia. • by contact e.g . • Plant viruses are spread by contact or insects. G Davidson

6. Viruses • Viruses invade cells by injecting their nucleic acid (either DNA or RNA) through their hollow tail into the cell. • The virus then takes control of the host cell’s biochemical activities, and, using the host’s nucleotides is able to replicate many copies of its own nucleic acids and protein shells. G Davidson

7. Viruses • This produces a host cell full of viruses all identical to each other which can then be released. • Some viruses attack bacteria and are called bacteriophages. G Davidson

8. Viruses • Some viruses can lie dormant inside cells for a long time before they reproduce. • Two American scientists Alfred Hersay and Martha Chase carried out experiments concerning the viral infection of a bacterium. G Davidson

9. Viruses • The experiments involved the use of the radioisotopes sulphur (35S) and phosphorous (32P). • The sulphur attaches itself to the protein coat of the bacteriophage and the phosphorous to the nucleic acid (this is because the coat contains sulphur but not phosphorous and vice versa). G Davidson

10. Experiment 1 Bacteriophages were labelled with 35S by growing them in a suspension of bacteria containing 35S. Experiment 2 Bacteriophages were labelled with 32P by growing them in a suspension of bacteria containing 32P. 32P 35S Hersey and Chase’s Experiments G Davidson

11. The radioactive bacteriophages were now incubated with non-radioactive bacteria. The radioactive bacteriophages were now incubated with non-radioactive bacteria. 32P now inside bacterium 35S Hersey and Chase’s Experiments G Davidson

12. Hersey and Chase’s Experiments The viral coats were separated from the bacterial cells in a blender. The resulting suspension was centrifuged. G Davidson

13. High concentration of 35S Low concentration of 32P Viral coats Low concentration of 35S High concentration of 32P Bacterial Cells Hersey and Chase’s Experiments G Davidson

14. Hersey and Chase’s Experiments High concentration of 35S Low concentration of 32P Viral coats Low concentration of 35S High concentration of 32P Bacterial Cells G Davidson

15. Defence (Vertebrates) • Once a micro-organism or virus has successfully bridged the first line of defences, various defence mechanisms are triggered. • To do this it must get through the skin into the body. G Davidson

16. Defence (Vertebrates) • The skin itself is a tough barrier, but if broken, blood clotting prevents microbe invasion. • We have other entry points which are also protected e.g. breathing system by cilia and mucus, wax in ears, lysozyme in eyes, etc. G Davidson

17. Defence (Vertebrates) • However, microbes can sometime get through these defences into our bodies where there is an excellent food supply and ideal temperatures for reproduction. • If microbes do get through, there are second line defences. G Davidson

18. Defence (phagocytes) • The blood contains white cells called phagocytes which are capable of engulfing bacteria by phagocytosis. • The phagocytes move towards the microbe by detecting chemicals released from it, and then ingest the microbe and destroy it using digestive enzymes in the lysosomes. G Davidson

19. Defence (Cellular) • Individual cells produce one of the interferons (protein family), if they are invaded by a virus. G Davidson

20. Defence (Cellular) • Thiscellular response is in responsea wide range of viruses and acts as a containment until the specific immune response takes over. G Davidson

21. Specific Immune Response • The types ofresponsesabove are examples of non-specific immunity, i.e. they give a wide protection. • Immunity is the ability to resist microbes. • The body also has a specific immune response system which is capable of fighting specific diseases or organisms. G Davidson

22. Specific Immune Response • Antigens are complex protein or carbohydrate molecules which the body cells are capable of recognising as foreign and dangerous. • Lymphocytes in the blood can recognise these antigens and produce antibodies specific to them in order to disable them. G Davidson

23. Specific Immune Response • Viruses have antigen sites on their protein coats which the antibodies lock onto in order to disable them. • An antibody is Y-shaped with receptor sites on each point of the Y, into which the antigen molecule fits. G Davidson

24. Specific Immune Response • One type of lymphocyte called B cells releases free antibodies into the • Other lymphocytes called NK (natural killer) cells have receptors on their surface which can identify invading cells and then destroy the infected cells with cytotoxic chemicals . G Davidson

25. Specific Immune Response • Once the virus or microbe has been destroyed, some of these cells remain in the system as memory cells and this allows the immune system to react faster the next time that particular antigen enters the system. G Davidson

26. Antibodies G Davidson

27. Antibody-Antigen Complex G Davidson

28. Bacteria breach the first line of defence and enter the animal’s body Foreign molecules on their surface act as ANTIGENS These are recognised as foreign by a certain type of host white blood cell called a LYMPHOCYTE. Immune Response (summary 1) G Davidson

29. These cells now respond by producing proteins of their own called ANTIBODIES These proteins may be released or may bind to the cell. In either case they attach themselves to several of the bacteria causing them to stick together in groups or agglutinate. Immune Response (summary 2) G Davidson

30. Now another form of the host’s white blood cell is attracted to the agglutinated bacteria. This type of cell is called a PHAGOCYTE. Immune Response (summary 3) This host cell now engulfs and destroys the bacteria in a process of PHAGOCYTOSIS. N.B. Not all invading bacteria are dealt with in this way. In some cases the antibodies lead to their death directly. G Davidson

31. Types of Specific Immunity and Rejection of Transplanted Tissue • There are two types of specific immunity: • Active Immunity • Passive Immunity G Davidson

32. Active Immunity • Active immunity is conferred on an individual when it produces its own antibodies in one of two ways • Naturally acquired immunity – the individual obtains immunity through contracting the disease e.g. measles. • Artificially acquired immunity – the individual obtains immunity through contact with a vaccine e.g. an injection of measles vaccine . G Davidson

33. Passive Immunity • Passive immunity is conferred on an individual when antibodies are given to them e.g.: • an injection of antibodies • antibodies from a mother’s milk • from blood across the placenta from the mother to the foetus . G Davidson

34. Blood Groups • The blood groups A, B, AB and O are determined by antigens of the surface of the red blood cells. • The plasma contains antibodies. G Davidson

35. Blood Groups • These are ‘ready made’ before birth • This is unusual as most antibodies are produced after the body has recognised a foreign antigen. G Davidson

36. Blood Groups • The antibodies in the plasma don’t match the antigens on the red blood cells. If they did then an antibody-antigen would occur and the blood would agglutinate. • This immune response would cause clots which could block arteries and veins. • The following table shows which antigens (Capital letters) and antibodies (lower case letters) are present in people with the various blood groups: G Davidson

37. Blood Group Antigen on Red Cell Antibody in Plasma A A b B B a AB A + B nil O nil a + b Blood Groups G Davidson

38. Blood Groups • This means that group O can donate blood to any group as it has no antigens to be agglutinated and is therefore said to be the universal donor. • Blood group AB is the universal recipient because it has no antibodies to agglutinate the donor’s antigens. G Davidson

39. Blood Groups • We can now see why it is important that the blood transfusion service and hospitals carry out tissue typing by identifying blood groups before transfusion: • Without this there would be a risk of tissue rejection. • In blood transfusions the problems of rejection are avoided by careful blood typing . G Davidson

40. Blood Groups • Without this there would be a risk of tissue rejection. • In blood transfusions the problems of rejection are avoided by careful tissue typing. • When organs are transplanted it is difficult to obtain an exact match unless genetically identical twins are used. G Davidson

41. Blood Groups • When organs are transplanted it is difficult to obtain an exact match unless genetically identical twins are used. • To overcome this problem the donor and the recipient are chosen to be as genetically similar as possible and then by using immunosuppressor drugs. G Davidson

42. Blood Groups • However, these reduce the efficiency of the recipient’s entire immune system and leave the patient open to serious diseases, e.g. pneumonia. • Scientists are now developing drugs which can overcome this problem. G Davidson

43. Cellular Defence in Plants • Like animals, plants respond at the whole plant level and the cellular level. G Davidson

44. Cellular Defence (Plants) Whole Plant barriers Cuticle Bark Physical barriers to infection Natural cell barrier Cell wall Plant Defence Barriers produced in response to infection Galls Extra lignin Chemical barriers produced in response to infection Next slide G Davidson

45. Antifungal chemical Phytoalexins Hydrogen peroxide Destroys chemicals produced by fungi Chemical barriers produced in response to infection Callose Prevents spread of microbes by blocking phloem seive tubes Accelerates the cutting and shedding of infected leaves to prevent spread Ethylene Affects protein therefore adversely affects viruses Tannins Cellular Defence (Plants) G Davidson