Topic 6 - Immunity, Infection, and Forensics

• There are 4 ways to determine time of death:

  • Body temperature
  • Rigor mortis
  • Decomposition
  • Forensics entomology
• After death, metabollic reactions will stop and the body will eventually cool until it reaches ambient temperature. The surroundings, position of the body, and clothing can affect this
• A dead body cools at usually 1.5C an hour
• Rigor mortis means stiffness of death
• Rigor mortis passes when muscles begin to break down
• The process of rigor mortis:

  1. Oxygen dependant reactions stop
  2. Anaerobic reactions produce lactic acid
  3. pH falls, enzymes are inhibited, anaerobic respiration is inhibited
  4. ATP is no longer produced, bonds between muscle proteins become fixed
• Signs of decomposition:

  • Putrefication (Green colouration of the skin)
  • Gas/liquid blisters on the skin
  • Unpleasant odour
  • Body bloating
• Autolysis is the process of the body's own enzymes breaking down cells
• The process of autolysis:

  1. The body's own enzymes from the digestive tract and lysosomes break down cells
  2. Bacteria from the gut and gas exchange system rapidly invade tissues
  3. The bacteria release enzymes that result in decomposition, the loss of oxygen in tissues favours anaerobic bacteria
  4. Organic carbohydrates, proteins, fats, and nucleic acids act as a food source for bacteria and fungi
• Forensic entomology is the use of the insects and their arthropod relatives that inhabit decomposing matter to aid legal investigation
• Life cycle of a blowfly:

  • Lay 150-200 eggs within 24 hours
  • 24 hours after laid, first stage larvae hatch
  • After another 24 hours, second stage maggots form
  • 24 hours later third stage maggots form
  • In 2-3 days third stage maggots turn into puparium
  • After 10 days puparium metmorphasise into flies
• Life cycle diagrams can be used to estimate time of death by checking what stage larvae are in or possibly other species and comparing to body farms
• Body farms put bodies in different conditions to use as a comparison standard
• Bacteria are present immediately after death, as bacteria decompose and digest body tissues they make favourable conditions for flies
• A DNA primer is a specific base sequence that anneals to the beginning of STR sequences, providing a place for DNA polymerase to bind
• Temperature increases rate of decomposition as it increases enzyme activity due to collision theory
• DNA primer, free nucleotides, DNA polymerase, and then DNA sample is needed for PCR
• PCR stands for polymerase chain reaction
• PCR amplifies the amount of DNA collected
• PCR

  1. All components are added to the reaction tube and heated to 95C to break hydrogen bonds in DNA
  2. Cooled to 50C and primers anneal to the start of STR sequences
  3. Heated to 70C so DNA polymerase can bind to primers and free complimentary nucleotides line up with STRs, making a replica of the original STR sample
• DNA molecules are negatively charged, if you apply an electrical current to a medium, they will move towards the positive electrode
• Gel electrophoresis:

  1. DNA fragments are loaded into agarose gel and submerged in buffer solution
  2. An electrical current is applied across the gel
  3. DNA fragments will move towards the positive electrode, the smaller the fragment, the further it will move
  4. Fluorescent probes are attached and bands are visualised underneath a UV light
• The lytic cycle is where the virus attaches itself onto a host cell and injects it's DNA into it. The cell then makes copies of the virus DNA, allowing it to replicate
• Lysogenic cycle:

  • Starts off the same as the lytic cycle
  • Genetic material stays hidden within the cell, whenever the cell replicates it also replicates the virus DNA
  • The lytic cycle is then triggered
• Genetic material in bacteria can be RNA or DNA, it is not histone bound and loose
• A pathogen is a microorganism that causes disease
• A local infection is limited to a specific part of the body
• A systematic infection is where pathogens have spread to the systems of the body
• Bacteriacemia is where is when a person's culture of blood reveals bacteria
• Septicemia is when bacteriacemia becomes systematic
• Skin flora are microorganisms that live on the skin which outcompete pathogens for space and water
• Skin is a waterproof protective layer that produces lipids with antimicrobial properties
• Histamines dilate capillaries which causes local heat that reduces pathogen reproduction
• Histamines cause the walls of capillaries to be leaky which forces plasma, white blood cells, and antibodies out
• When a pathogen invades, the hypothalamus sets a higher body temperature which reduces pathogen reproduction rate
• In viral infections temperature spikes when viruses burst out of cells
• Inflammation is localised to the damaged tissue and is caused by mast cells and damaged white blood cells releasing histamine
• More wide-spread inflammation results in a rash
• Lysozymes are enzymes found in tears, saliva, and nasal secretions that kill bacteria by breaking down their cell walls
• Interferon is a virus specific defense