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Bio Topic 6 - Forensics (Time of Death (Extent of Decomposition …

- - - - due to lack of O2, muscles now have to respire anaerobically leading to a build up of lactic acid
        
        the lactic acid decreases the pH of the cells, creating a hostile environment for enzymes which produce ATP, inhibiting their function.
        
        No ATP makes the Actin-myosin cross-bridge bonds in muscle cells to become fixed (muscle contraction) and the body becomes stiff.
        
        small muscles stiffen first (e.g. in the head/ jaw cheeks), then the larger muscles in the lower body stiffen (e.g. leg).
        
        Affected by muscle development and temperature - e.g. high temp increases metabolic rate and so rigor mortis occurs quicker as more lactic acid is produced in a shorter time.
  - - - scientists establish TOD according to what stage of succession the body is in
        
        Stage 4 - as a dead body dries out, conditions become less favourable for flies - they leave the body. Beetles remain as they decompose dry tissue.
        
        Stage 3 - When fly larvae feed on a dead body. they make conditions favourable for beetles, so beetles move in.
        
        Stage 2 - as bacteria decompose tissues, conditions in a dead body become more favourable for flies and their larvae.
        
        Stage 5 - When no tissue remains, conditions are no longer favourable for most organisms.
        
        Stage 1 - Immediately after the TOD, conditions in a dead body are most favourable for bacteria
  - - - Human bodies cool at a rate of 1.5-2 degrees per hour so forensic scientists can work out the TOD
  - - - TOD estimated by identifying the type of insect present on the body and what stage of its lifecycle its currently in
        
        conditions such as drugs, humidity, temp and oxygen availability will have a effect on an insects life cycle
      - e.g. blowfly larvae hatches 24 hours after they're laid. If blowfly eggs are found on a body it is likely that the individual has been dead less than 24 hours.
  - - - immediately after death cells/ tissues are decomposed by the body's own enzymes and bacteria
      - Skin on the body turns a greenish colour
    - - Microbes decompose tissues and organs producing gases, such as methane, causing the body to bloat
      - Skin starts to blister and fall off
    - - Tissues begin to liquify and seep out into the area around the body
    - - Only a skeleton remains
    - - the skeleton begins to disintegrate until there's nothing left of the body
- - - - Used to make millions of copies of specific regions of DNA in a matter of hours
        
        A reaction mixture of the DNA sample, free nucleotides, primers and taq polymerase
        
        Primers are short pieces of DNA complementary to the bases at the start of the fragment you want
      - The DNA mixture is heated to 95 degrees C to break the hydrogen bonds between 2 strands of ds DNA.
        
        a fluorescent tag is added v - added to DNA fragments so they can be viewed under UV light
        
        Gel Electrophoresis is used to separate the DNA fragments according to their length.
        
        An electrical current is passed through the gel - negatively charged DNA fragments (all fragments) move toward the anode (positive electrode) at the end of the gel
        
        The gel is viewed under UV light
        
        Fragments appear as bands under UV light - the DNA profile
        
        Two DNA profiles can be compared to see how similar the pattern of bands on the gel - a match could help identify an individual or determine a genetic relationship
        
        Short DNA fragments travel further through the gel as they are less dense and so fragments separate according to length.
        
        DNA is placed in a well in a slab of gel, covered in a buffer solution that conducts electricity
      - Mixture is then cooled to 50 degrees C so primers can anneal (attach) to the strands
      - The reaction mixture is then heated to 72 degrees C so the taq polymerase can blind to DNA strands,
      - Taq polymerase lines free nucleotides alongside each template strand, making complementary strands of DNA
      - Two new copies of the desired sequence of DNA are formed and one cycle of PCR is complete
      - cycle starts again
      - Each PCR cycles, doubles the amount of the desired sequence of DNA
  - - - DNA is isolated
        
        Amplified using PCR
        
        PCR products are run on an electrophoresis gel and profiles produced are compared to suspects
    - - the more bands that match, the more closely related (genetically similar) the two people are.
        
        used in paternity tests
- - - - Cell Wall
      - Capsule
        
        made up of secreted 'slime', protecting the bacterium from attack by cells of the immune system
      - Flagellum
      - Plasmids (DNA)
        
        not present in all bacteria - small loops of DNA not part of the chromosome
      - Ribosomes
      - Circular DNA
      - Pili
      - Cytoplasm
      - Difference in structure is that virus' do not have a plasma membrane, cytoplasm or ribosomes
      - Plasma Membrane
        
        may contain folds called mesosome
  - - - Core of Nucleic acid
        
        Could be either DNA or RNA - HIV has RNA
      - Proteins inside their capsid
        
        HIV has reverse transcriptase
      - Attachment Proteins
        
        stick out from the edge of the capsized/ envelope, letting the virus cling onto a suitable host cell.
      - Envelope
        
        not all virus' have this stolen extra outer layer from the cell membrane of a previous host cell.
      - Capsid
        
        Protein Coat around the core