Topic 6

• Modern-day drug trials

  • Safer than William Withering's trials
  • More valid than William Withering's trials
  • More reliable than William Withering's trials
• Safer modern drug trials


  • Use pure drugs instead of crude extracts
  • Pre-testing on cells and animals occurs before human trials
  • Drug development is regulated by stringent legislation
• More valid modern drug trials


  • Placebos are used for comparison to ensure the effectiveness of the drug
  • Double-blind trials are conducted to eliminate bias
  • Factors such as age and lifestyle of participants are controlled
• More reliable modern drug trials


  • A larger number of participants are tested
  • Results are analyzed using statistical methods to ensure accuracy and reliability
• Determining time of death of a mammal

  1. Extent of decomposition

  2. Forensic entomology

  3. The stage of succession

  4. Body temperature

  5. Degree of muscle contraction
• Decomposition


  Bodies usually follow the same pattern of decay and decomposition, starting with the enzymes from the digestive system breaking down the surrounding tissues while cells begin to release enzymes as they are broken down
• Forensic entomology


  The study of insects to determine the time of death. Each species of insects has a specific life cycle. Determining the age of insects present enables the time of death to be determined
• Stage of succession


  As the body decays, the species colonising the body change. Therefore, analysis of the community of species present can be used to determine time of death
• Body temperature


  Temperature of the body begins to decrease after death as heat-producing metabolic reactions stop. However, temperature can only be used to determine time of death in the first 24 hours, until the body reaches the temperature of its surroundings
• Rigor mortis


  After death muscles begin to stiffen as ATP is used up, calcium ions build up in the muscle cells and they become fixed in a state of contraction. The extent of rigor mortis can be used to determine time of death
• Microorganisms


  Bacteria and fungi play an important role in the decomposition of organic matter and the recycling of carbon (releasing nutrients that were locked up in organic material)
• Bacteria and fungi


  Secrete enzymes that decompose dead organic matter into small molecules which they then use as respiratory substrates - carbon dioxide and methane are released in this process, thus recycling carbon
• Introns


  Non-coding regions of DNA
• Exons


  Coding regions of DNA
• Short-tandem repeats


  Repeating base sequences in introns
• Satellites


  Sections of DNA containing short-tandem repeats
• Polymerase Chain Reaction


  1. A reaction mixture is set up by mixing the DNA sample, primers, free nucleotides and DNA polymerase

  2. The mixture is then heated to 95 degrees to break the hydrogen bonds and to separate the two strands for around 30 seconds

  3. The mixture is then cooled to a temperature between 50-65 degrees so that the primers can bind to the strands, this takes around 20 seconds

  4. Temperature is increased to about 70 degrees as this is the temperature DNA polymerase works at. DNA polymerase creates a copy of the sample by complementary base pairing using the free nucleotides. The mixture is left for at least one minute for the sample to be amplified. The cycle can then be repeated many times and gives rise to an amount of DNA sufficient to create a DNA profile
• DNA profiling


  A forensic technique used for identification and determining genetic relationships between organisms
• Gel electrophoresis


  1. Fragments of DNA are cut with restriction endonuclease enzymes (either side of satellites)

  2. These fragments are placed in wells in agarose gels and dyed with ethidium bromide so they fluoresce under UV light. A current is then applied to the gel. DNA is negative hence moves towards the anode. Fragments of different sizes move at different speeds, according to mass so 'bands' appear

  3. A nylon or nitrocellulose filter is placed on top of the plate - the dry, absorbent material draws solution containing DNA fragments to the filter. The fragments appear as 'blots'

  4. Gene probes (complementary sequences labeled with fluorescent or radioactive markers) are added and bind with the DNA in a process known as hybridisation

  5. 'Blots' compared and number of satellites visualised
• Mini/microsatellites


  Repeated sequences of DNA in introns
• Viruses


  Non-living structures which consist of a nucleic acid (either DNA or RNA) enclosed in a protective protein coat called the capsid, sometimes covered with a lipid layer called the envelope
• Differences between bacteria and viruses


  • Bacteria are prokaryotes, meaning that they have no membrane-bound organelles - their genetic material is found in the form of a circular strand of DNA. Viruses consist of just nucleic acid (DNA or RNA) enclosed in the protein coat
  • Bacteria do not require a host to survive, whereas viruses do not carry out the processes that define a living organism, they are entirely dependent on their hosts and cannot survive without them; consequently they are not classified as living organisms
  • Viruses are significantly smaller than bacteria
  • Bacteria have a cell membrane, cell wall and cytoplasm, as well as other organelles such as ribosomes, plasmids, flagellum and pili. Viruses possess no such structures
• Tuberculosis (TB)


  A bacterial disease caused by Mycobacterium tuberculosis which infects phagocytes in the lungs. First infection may be symptomless. Infected phagocytes are sealed in tubercles in the lungs as a result of an inflammatory response. Bacteria lie dormant inside the tubercles. When the immune system becomes weakened, the bacteria become active again, and slowly destroy the lung tissue, thus leading to breathing problems, coughing, and weight loss, as well as fever. TB can then spread to other areas of the body, at which stage it can be fatal
• Human Immunodeficiency Virus (HIV)


  A viral infection that destroys T helper cells in the immune system leading to AIDS. The first symptoms of HIV are flu-like including fevers, tiredness and headaches. After several weeks HIV antibodies appear in blood, thus making a person HIV positive. After this period, the symptoms disappear until the immune system becomes weakened again, thus leading to AIDS. Symptoms of AIDS include weight loss, diarrhoea, dementia, cancers and opportunistic infections such as TB. These opportunistic infections can lead to death
• Physical barriers to infection

  • Skin - a tough physical barrier consisting of keratin
  • Stomach Acid (hydrochloric acid) and enzymes - which kills bacteria
  • Gut and skin flora - natural bacterial flora competes with pathogens for food and space
• Non-specific response


  • Inflammation
  • Fever
  • Lysozyme action
  • Phagocytosis
• Inflammation


  Histamines released by damaged white vessels cause vasodilation, which increases the flow of blood to the infected area and increases permeability of blood vessels. As a result, antibodies, white blood cells and plasma leak out into the infected tissue which can help to destroy the pathogen
• Fever


  The hypothalamus sets body temperature higher, increasing the rate of enzyme-controlled reactions. This decreases speed of pathogen reproduction and increases rate of specific immune response. A careful balance must be struck between harming the pathogen and denaturing enzymes in the body
• Lysozyme


  An enzyme found in secretions such as tears and mucus which kills bacteria
• Specific immune response


  Antigen-specific and produces responses specific to one type of pathogen only
• Lymphocytes involved in specific immune response

  • B cells
  • T cells
• Humoral response


  1. T helper activation

  2. Effector stage
• Cell-mediated response


  1. Pathogen invades host cell

  2. T killer cell binds to antigen-presenting cell

  3. T killer cell divides

  4. Active T killer cells lyse infected cell
• Active immunity


  Immunity resulting from the production of antibodies by the immune system in response to the presence of an antigen
• Passive immunity


  Immunity resulting from the introduction of antibodies from another person or animal
• Types of immunity


  • Natural active
  • Natural passive
  • Active artificial
  • Passive artificial
• Herd immunity


  Enough people have been vaccinated to make transmission of a disease very unlikely (requires 80-90% vaccination)
• Immunisation


  The process of protecting people from infection with passive or active artificial immunity via vaccination
• Vaccination


  The process by which immunisation is achieved, using live but weakened strains of a pathogen or inactivated/killed pathogens/toxins
• Vaccination


  1. Primary immune response produces memory cells

  2. Secondary immune response is faster and greater antibody production