topic 6

• extent of decomposition


  bodies usually follow the same pattern of decay and composition, starting with the enzymes from the digestive system breaking down the surrounding tissues. Therefore a stage of decomposition can be used to determine how long a body has been dead.
• forensic entomology


  is 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 time of death to be determined
• stage of succession


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


  temperature of the body begins to drop after death as heat-producing metabolic reactions stop. Temperature can only be used to determined time of death in the first 24 hours, until the body reaches the temperature of its surroundings. This also depends on size of body and weather conditions
• degree of muscle contraction


  rigor mortis: after death muscles begin to stiffen as ATP is used up, calcium ions build up in muscle cells and they become fixed in a state of contraction

  extent of rigor mortis can be used to determine time of death. stiffness begins 2-4 hrs after death and only lasts around 36 hrs so limited use.
• what role do microorganisms play in the decomposition of organic matter and recycling of carbon?


  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 the process
• what are exons and introns?


  exons are sections of genetic material that code for proteins.

  introns are sections of genetic material which do not code for proteins. the introns consist of many repeating base sequences known as short tandem repeats in satellites
• how can DNA fragments be amplified in vitro


  polymerase chain reaction (PCR)
• Step 1 of PCR


  set up a reaction mixture containing DNA sample, primers, free nucleotides and DNA polymerase
• Step 2 of PCR


  heat the mixture to 95 degrees to break the hydrogen bonds and separate the two strands
• Step 3 of PCR


  cool the mixture to 50-65 degrees depending on the type of primers used, so the primers can. bind to the strands
• Step 4 of PCR


  increase temperature to around 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 cycle is then repeated to give rise to a sufficient amount of DNA
• what is DNA profiling


  a forensic technique used for identification and determining specific relationships between organisms.
• Step 1 gel electrophoresis


  fragments of DNA are cut with restriction endonuclease enzymes (either side of satellites)
• step 2 gel electrophoresis


  fragments are then loaded into wells in agarose gels and dyed with ethidium bromide. a current is then applied to the gel. DNA is negative so moves towards the anode, different sizes move at different speeds according to mass so bands appear
• Step 3 of gel electrophoresis


  a nylon or nitrocellulose filter is placed on top of the plat- the material draws solution containing DNA fragments to the filter. the fragments appear as blots
• Step 4 of gel electrophoresis


  gene probes (complementary sequences labeled with fluorescent or radioactive markers) are added and bind with the DNA in a process known as hybridisation
• Step 5 of Gel Electrophoresis


  'blots' compared and number of satellites visualised. repeated sequences of DNA in introns are referred to as mini satellites depending on their size. the more closely related people are, the more similar the repeats are.
• what are viruses?


  non-living structures which consist of a nucleic acid (DNA/RNA) enclosed in a protective protein coat called the capsid
• bacteria are prokaryotes ...


  meaning they have no membrane-bound organelles and their genetic material is found int he form of a circular strand of DNA. viruses consist of just nucleic acid in the protein coat
• bacteria do not require a host to survive ...


  whereas viruses not carry out the processes that define a living organism, they are dependant on their hosts and can't survive without them
• tuberculosis


  a bacterial disease called mycobacterium tuberculosis which infects phagocytes in the lungs
• step 1 of TB


  first infection may be symptomless. infected phagocytes are sealed in the lungs as a result of an inflammatory response.
• step 2 of TB


  bacteria lie dormant inside the tubercles. they are not destroyed by the immune system, as tubercles are covered with a thick waxy coat
• step 3 of TB


  when the immune system become weakened, the decateri become active again and slowly destroy the lung tissue. this leads to breathing problems, coughing, weight loss and fever
• step 4 of TB


  TB can then spread to other areas of the body at which stage it can be fatal
• human immunodeficiency virus (HIV)


  destroys T-helper cells in the immune system leading to AIDS
• step 1 of HIV


  the first symptoms of HIV are flu-like including fevers, tiredness and headaches
• step 2 of HIV


  after several weeks HIV antibodies appearing blood, making a person HIV positive
• step 3 of HIV


  after this period, the symptoms disappear until the immune system becomes weakened again leading to AIDS
• symptoms of AIDS


  weight loss, diarrhoea, dementia, cancers and opportunistic infections such as TB
• physical barriers to skin infection


  skin: a tough physical consisting of keratin

  stomach acid: kill bacteria

  gut and skin flora: natural bacterial flora competes with pathogens for food and space
• non specific response


  the body can respond to pathogens without recognition of their antigens
• inflammation


  histamines released by damage white vessels cause vasodilation, which increases the flow of blood to the infected are and increases permeability of blood vessels. because of this, 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 the speed of pathogen reproduction and increases the rate of specific immune response.
• lysozyme action


  lysozyme is an enzyme found in secretions such as tears and mucus which kills bacterial cells by damaging their cell wall, causing lysis
• phagocytosis


  a process in which white blood cells engulf pathogens; destroying them by enclosing a pathogen and denaturing enzymes in the body
• specific immune response


  antigen specific and produces responses specific to one type of pathogen only
• this type of immune response relies on lymphocytes produced in the bone marrow


  B cells mature in the bone marrow and are involved in the humoral response.

  T cells move rom the bone marrow and to the thymus gland where they mature, the are involved in both humeral and cell-mediated response
• T helper activation


  1. bacterium is engulfed by a macrophage and antigens are displayed on the surface of the macrophage on MHC's. the macrophage acts as an antigen-presenting cell

  2. macrophage APC binds to T helper cell with complementary receptor proteins

  3. the T helper cell is 'activated' and divides by mitosis to form T memory cells and active T helper cells