bio topic 6

• Polymerase Chain Reaction


  1. DNA polymerase sets up a reaction

  2. The mixture is heated to 95 degrees to separate the two strands for around 30 seconds

  3. The mixture is then cooled to a temperature that allows the primers to bind
• Temperature is increased for the Polymerase Chain Reaction to work
• Forensics and Time of Death


  • Extent of decomposition
  • Forensic entomology
  • Stage of succession
  • Body temperature
  • Degree of muscle contraction
• Extent of 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
• Degree of muscle contraction


  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. This is called rigor mortis, and the extent of rigor mortis can be used to determine time of death
• Microorganisms such as 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, releasing carbon dioxide and methane
• Introns


  Non-coding regions of DNA
• Exons


  Coding regions of DNA
• Short-tandem repeats


  Repeating base sequences in the introns
• The introns consist of many repeating base sequences known as short-tandem repeats in sections known as satellites
• DNA profiling


  1. Sample amplification using Polymerase Chain Reaction

  2. Reaction mixture set up

  3. Mixture heated to 95 degrees

  4. Mixture cooled to 50-65 degrees

  5. Temperature increased to 70 degrees
• DNA profiling


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


  1. DNA fragments cut with restriction endonuclease enzymes

  2. Fragments placed in wells in agarose gels and dyed

  3. Current applied to gel

  4. DNA moves towards anode

  5. Bands appear
• DNA blotting


  1. Nylon or nitrocellulose filter placed on gel

  2. DNA fragments drawn to filter

  3. Gene probes added and bind to DNA

  4. Blots compared and satellites visualised
• Mini/microsatellites


  Repeated sequences of DNA in introns
• Viruses


  Non-living structures consisting of nucleic acid (DNA or RNA) enclosed in a protective protein coat
• Bacteria


  • Prokaryotes with genetic material in the form of a circular strand of DNA
  • Have a cell membrane, cell wall and cytoplasm, as well as other organelles
• Viruses


  • Consist of just nucleic acid (DNA or RNA) enclosed in a protein coat
  • Do not carry out the processes that define a living organism, entirely dependent on hosts
• Bacterial disease


  • Tuberculosis (TB)
• Tuberculosis


  1. First infection may be symptomless

  2. Infected phagocytes sealed in tubercles

  3. Bacteria lie dormant in tubercles

  4. Bacteria become active when immune system weakened

  5. Destroy lung tissue leading to symptoms
• Viral infection


  • Human Immunodeficiency Virus (HIV)
• HIV infection


  1. First symptoms are flu-like

  2. HIV antibodies appear after several weeks

  3. Symptoms disappear until immune system weakened, leading to AIDS
• Physical barriers to infection


  • Skin
  • Stomach acid and enzymes
  • Gut and skin flora
• Non-specific immune response


  Body responds to pathogens without recognition of their antigens
• Non-specific immune response


  1. Inflammation

  2. Fever

  3. Lysozyme action

  4. Phagocytosis
• Specific immune response


  1. Relies on lymphocytes produced in bone marrow

  2. B cells mature in bone marrow

  3. T cells mature in thymus gland
• Humoral immune response


  1. Macrophage presents antigens to T helper cell

  2. T helper cell activates and divides

  3. B cell binds to antigens and is activated by T helper cell

  4. B cells differentiate into plasma cells that produce antibodies

  5. Antibodies destroy pathogens
• Cell-mediated immune response


  1. Host cell displays antigens and becomes APC

  2. Killer T cell binds to APC and secretes chemicals to lyse infected cell
• Active immunity


  Immune system produces antibodies in response to antigen
• Passive immunity


  Antibodies introduced from another person or animal
• Natural active immunity


  Arises from exposure to an antigen/getting the disease
• Natural passive immunity


  Mother's antibodies cross the placenta and are present in breast milk
• Active artificial immunity


  Acquired through vaccinations that stimulate the immune system
• Passive artificial immunity


  Antibodies are injected into the body
• Herd immunity


  Enough people vaccinated to make disease transmission very unlikely
• Immunisation


  Protecting people from infection with passive or active artificial immunity via vaccination