1 Deadlines/Homework 12C Complete the remainder of the homework booklet to hand in on Friday 5th February. Revise for a test on Section 3.2 (Cells) on Friday 12th February. 12D Complete the remainder of the homework booklet to hand in on Thursday 4th February. Revise for a test on Section 3.2 (Cells) on Thursday 11th February.
2 HIV, Monoclonal Antibodies and the ELISA test
3 Boardworks AS Biology Infectious DiseasesTeacher notes In ‘Slide Show’ mode, click the name of a section to jump straight to that slide.
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5 Boardworks AS Biology Infectious DiseasesWhat are HIV and AIDS? In 2007, 33.2 million people were estimated to be living with the human immunodeficiency virus (HIV). HIV is a retrovirus that causes acquired immune deficiency syndrome (AIDS) – a deterioration of the immune system. Photo credit: C Goldsmith / CDC Scanning electron micrograph of HIV-1 budding from cultured lymphocyte. Multiple round bumps on cell surface represent sites of assembly and budding of virions. Data from AVERT (www.avert.org) There is currently no cure for infection with HIV; however, antiretroviral drugs have been developed to help delay the onset of AIDS.
6 Boardworks AS Biology Infectious DiseasesHIV replication
7 Effect of HIV on the immune systemBoardworks AS Biology Infectious Diseases Effect of HIV on the immune system Teacher notes The course of the disease and the life expectancy of an individual will vary with: the patient’s health before infection the patient’s genetic resistance to the disease the quality of the immune response to the initial infection the availability of drug treatment (currently expensive and complicated). A small proportion of people infected with the virus develop AIDS and die within months following primary infection, while approximately 5% of HIV-infected individuals exhibit no signs of disease progression even after 12 or more years. See the ‘Immunology’ presentation for more information about lymphocytes and the immune system.
8 AIDS – Acquired Immune Deficiency syndromeThe decrease in the number of helper T-cells eventually means the patient is unable to defend themselves against other pathogens. Patients die from common diseases, tumours and opportunistic infections, e.g. TB or pneumonia.
10 Stages of HIV infectionBoardworks AS Biology Infectious Diseases Stages of HIV infection Replace circles with outline of HIV taken from animation
11 HIV diagnosis and transmissionBoardworks AS Biology Infectious Diseases HIV diagnosis and transmission Teacher notes This graph could be used as a starter for discussion, such as: What control programmes could be put in place to decrease the transmission within each group? Education, clean needles, etc. Why might the numbers not be representative of the transmission each year? (Year reported isn’t necessarily year contracted, some people may not be diagnosed) Which group should be a priority for a control campaign and why? Does this data surprise you? Why do you think transmission rates have increased?
12 Boardworks AS Biology Infectious DiseasesAntiretroviral drugs Modern antiretroviral drugs are designed to reduce the production of HIV by targeting different stages of its lifecycle. reverse transcriptase inhibitors prevent viral RNA being copied into DNA for protein synthesis. protease inhibitors inhibit proteases used in the synthesis of viral proteins. Photo credit: Wellcome Library, London Retrovir is an antiretroviral drug - the first approved for treatment of HIV. Teacher notes The photo shows azidothymidine (AZT), the first approved antiretroviral drug for treatment of HIV. It acts as a reverse transcriptase inhibitor. A combination of several (typically three or four) antiretroviral drugs is known as Highly Active Anti-Retroviral Therapy (HAART). HIV can develop resistance to these drugs so they are often taken in combination.
13 Why not use antibiotics?Boardworks AS Biology Infectious Diseases Why not use antibiotics? Antibiotics are a group of drugs used to treat bacterial infections. There are two different types of antibiotics: bactericidal – kill bacterial cells bacteriostatic – slow the growth or reproduction of bacteria. Some antibiotics prevent the formation of bacterial cell walls, resulting in osmotic lysis. Photo credit: P Ferguson, ISM / Science Photo Library Coloured transmission electron micrograph (TEM) of a section through bacteria (red) being killed (yellow remnants) by the use of the antibiotic drug ceftazidine. These bacteria are Staphylococcus aureus bacteria that can cause endocarditis (internal heart inflammation). This can be treated with ceftazidine. Magnification unknown. Teacher notes Antibiotics were originally obtained directly from organisms such as the Penicillum fungus, but many can now be produced by chemical synthesis. See the ‘Transport Across Membranes’ presentation for more information about osmosis and lysis. Antibiotics do not destroy viruses – suggest why.
14 Why don’t antibiotics destroy viruses?Viruses are found inside host cells so are difficult to target Many antibiotics target the production of the cell wall (murein – a peptide). Viruses have a protein coat so are unaffected.
15 DNA replication and HIV treatment Answer the questions
16 DNA replication and HIV treatment 1 a W = cytosine (1 mark) X = deoxyribose (1 mark) Y = phosphate (1 mark) Z = thymine (1 mark)
17 b Any two of: the base uracil is substituted for thymine; (1 mark) DNA contains deoxyribose, RNA contains ribose sugar; (1 mark) DNA is double stranded, RNA is single stranded. (1 mark)
18 2 a S phase (1 mark) b DNA polymerase (1 mark) free (DNA) nucleotides. (1 mark) c Bases combine in complementary base pairing; (1 mark) A with T, C with G (1 mark) d The new DNA molecule is made of two strands; (1 mark) one original parent strand, one new strand. (1 mark)
19 3 a AZT has no phosphate group; (1 mark) AZT has substituted the OH (on the sugar) with N3 (1 mark) b AZT will combine with adenine; (1 mark) as it is a similar shape to thymine/or complementary shape to adenine. (1 mark)
20 c It would be unable to make a sugar phosphate backbone/won’t combine with the phosphate on the neighbouring nucleotide. (1 mark) d The virus is unable to make DNA so can’t reproduce. (1 mark)
21 Boardworks AS Biology Infectious DiseasesHIV and AIDS
22 Monoclonal Antibodies and the ELISA test
23 What are monoclonal antibodies?Boardworks AS Biology Immunology What are monoclonal antibodies? Polyclonal antibodies are naturally produced in an immune response. Different plasma cells secrete antibodies, resulting in a variety of different antibodies against a specific antigen. Monoclonal antibodies (mAbs) are antibodies produced from clones of a single plasma cell and are therefore all identical. They have many important uses, such as: the treatment of cancer and other diseases drug screening home pregnancy kits scientific research. Photo credit: Jupiterimages Corporation Teacher notes The different types of polyclonal antibodies produced in an immune response will bind to a different epitope (part of the antigen). The method of obtaining monoclonal antibodies was developed by Georges Kohler and Cesar Milstein in In 1984 they were awarded a Nobel prize for their work. Monoclonal antibodies can be very useful in scientific research. For example, they have been used to pinpoint and identify antigens on the surface of a parasite, helping researchers develop a vaccine. There are over 20 approved mAb therapies, most of which treat either: cancer (e.g. colorectal and breast cancer, B cell leukaemia, non-Hodgkin’s lymphoma) auto-immune inflammatory diseases (e.g. rheumatoid arthritis, Crohn’s disease, ankylosing spondylitis, psoriasis)
24 Production of monoclonal antibodiesBoardworks AS Biology Immunology Production of monoclonal antibodies Large quantities of mAbs can be produced using mice or rabbits. A specific antigen is injected into the animal, stimulating the production of plasma cells. The plasma cells are removed from the animal and fused with cancerous myeloma cells from normal mice. These form immortal hybridoma cells, which can produce a single type of antibody indefinitely. Photo credit: Steve Gschmeissner / Science Photo Library Coloured transmission electron micrograph (TEM) of mouse leukaemia particles (green) outside a hybridoma cell. This is a man-made hybrid cell used in the production of monoclonal antibodies. Hybridomas are produced after injecting a mouse with a foreign substance (antigen), harvesting its antibody-producing white blood cells (plasma cells) and fusing them with myeloma cells (cancerous plasma cells). Fusing plasma and myeloma cells allows hybridomas to grow indefinitely in culture. The hybridoma cells are cloned and tested for the desired antibody. The desired clones are grown in culture and their antibodies harvested. Magnification: x12,000 when printed 10 centimetres wide. Teacher notes Plasma cells alone are not suitable for mass production of monoclonal antibodies as they only function for a few days in culture.
25 Production of monoclonal antibodiesBoardworks AS Biology Immunology Production of monoclonal antibodies The problem with using mouse-derived (murine) mAbs in humans is that they may be recognized as foreign. This will trigger an immune response, which quickly inactivates the mAbs. murine The immune response can be minimized by using genetic engineering to create humanized mAbs. These consist of mainly human polypeptide chains, with only the amino acids at the antigen-binding site derived from mice. Teacher notes Other developments to create mAbs that won’t trigger an immune response include creating transgenic mice that will naturally produce fully human antibodies when injected with an antigen. Students could discuss the ethics relating to producing monoclonal antibodies in humans. humanized
26 Exam question – monoclonal antibodiesRemember: Antigen injected into animal Plasma cells produced Plasma cell fused with myeloma (cancer) cell Hybridoma cell formed – multiplies quickly and indefinitely to produce many identical antibodies (for the original antigen).
27 ELISA Enzyme-linked immunosorbent assay Tests for the presence of particular antigens or antibodies in a sample.
28 ELISA Direct ELISA – uses monoclonal antibodies to test for an antigenELISA Direct ELISA – uses monoclonal antibodies to test for an antigen. Indirect ELISA – uses an antigen to test for an antibody. In both cases, a positive result is seen as a change in colour. An enzyme bound to an antibody is added to the plate. If it binds, the enzyme changes the colour of a substrate.