Topic 6

• Forensic scientists are involved in the collection and analysis of evidence during an investigation of criminal activities
• Determining the time of death

  Circumstances surrounding the death of a person can be revealed by determining the time of death of a body
• Changes that occur to the body after death


  • Physical and chemical changes
• Measurements forensic scientists take

  • Core body temperature
  • Degree of rigor mortis
  • State of decomposition
  • Forensic entomology
  • Succession on corpses
• Core body temperature


  36.2 – 37.6 degrees Celsius is the normal range for a human's body temperature
• Cooling (algor mortis)


  Rapid drop in body temperature to the ambient temperature due to radiation, conduction, convection, and evaporation of water
• Measuring core body temperature

  Long thermometer with greater range used, rather than usual clinical/digital thermometer
• Factors affecting post-mortem cooling

  • Size of body
  • Ambient temperature
  • Position of body
  • Presence of clothing
  • Humidity
  • Air movement
  • Water
• Rigor mortis


  Muscles stiffen after death due to lack of oxygen, meaning that muscle cells will respire anaerobically, producing lactic acid
• Rigor mortis


  • Joints are fixed in whatever position at death, then relax
  • Begins in small muscles in the head and ends in larger muscles in the body
  • Affected by level of muscle development and the temperature
• Decomposition


  Decomposition begins soon after death and is carried out by decomposers (e.g. bacteria and fungi)
• Decomposition


  • Autolysis - tissues start to break down due to enzymes produced by the body
  • Green skin on abdominal skin
  • Gas released by bacterial metabolism causes bloating
  • Skin will blister and fall off
  • Soft tissues will turn to liquid
  • Process continues until only a skeleton remains
• Forensic entomology


  Samples of insects near and on the body are collected to help determine time of death
• Forensic entomology


  • Different insects colonise the body at different times after death
  • The life cycle of the insect can also help to determine time of death
  • Air, ground, body temperature and maggot mass can determine the rate of development
• Succession on corpses


  The change in the type of organism found in a dead body over time
• Succession on corpses


  • Stages of succession above ground
  • Succession stages will differ depending on the location of the body and exposure to environmental factors
• Decay/decomposition is when waste products or dead organisms are broken down and the materials they contain (e.g. carbon and mineral ions) are returned to the environment
• Decomposers


  Bacteria and fungi that break down large organic molecules into smaller ones
• How decomposers break down dead matter


  • Secreting enzymes on the surface
  • Absorbing the small soluble food molecules
  • Releasing CO2 and methane into the atmosphere
• CO2 can be absorbed by green plants, which will fix carbon into carbohydrates in photosynthesis
• DNA profiling


  Every person has a unique DNA sequence that can create a DNA profile, which can be used to identify individuals in forensic science and genetic relationships
• Creating a DNA profile

  1. Isolating a sample of DNA

  2. Using PCR to produce more copies of DNA fragments

  3. Carrying out gel electrophoresis

  4. Analysing the pattern
• Polymerase chain reaction (PCR)


  An in vitro method of DNA replication that amplifies DNA by producing many copies of a section of DNA
• PCR


  • Requires DNA polymerase, free nucleotides, DNA/RNA sample, DNA primers, and buffer solution
  • Stages include denaturation, annealing, and elongation/extension
• Gel electrophoresis


  Allows analysis of DNA, RNA and proteins by separating them based on their size/mass as they move through the agar gel
• Gel electrophoresis


  • DNA molecules move from cathode to anode due to negative charge
  • Smaller fragments move faster through the pores
  • Probes are added to create a pattern of bands
• DNA profiling


  Can determine genetic relationships between people by comparing DNA fragment lengths
• Uses of DNA profiling

  • Paternity tests
  • Selective/captive breeding programmes
• Bacteria


  Single-celled prokaryotes that lack membrane-bound organelles and have a circular chromosome
• Structures found in bacteria

  • Cell wall
  • Cell surface membrane
  • Cytoplasm
  • Circular DNA
  • Ribosomes
  • Flagellum
  • Capsule
  • Infolding of cell surface membrane
  • Plasmid
  • Pili
• Viruses


  Non-cellular infectious particles with a nucleic acid core and a capsid, some have an envelope
• Viruses don't have plasma membranes, cytoplasm, or ribosomes
• Viruses

  • Some contain proteins inside the capsid that perform a variety of functions
  • Viruses contain attachment proteins that enable them to bind to host cells
• Flagella


  • Tail-like structure that rotate for movement
• Pili


  • On surface of bacteria that allows them to attach to other cells or surfaces
  • Involved in gene transfer during sexual reproduction
• Components always present in bacteria

  • Cell wall
  • Cell surface membrane
  • Cytoplasm
  • Circular DNA
  • Ribosomes
• Components sometimes present in bacteria

  • Flagellum
  • Capsule
  • Infolding of cell surface membrane
  • Plasmid
  • Pili
• Viruses


  • Non-cellular infectious particles
  • Simple in structure and smaller than prokaryotic cells
  • Have a nucleic acid core (single/double RNA/DNA) and a capsid
  • Don't have plasma membranes, cytoplasm, or ribosomes
  • Some have an envelope formed from the membrane-phospholipids of the cell they were made in
  • Some contain proteins inside the capsid that perform a variety of functions (e.g. HIV contains reverse transcriptase)
  • Contain attachment proteins that protrudes from the capsid/envelope, which enables the virus to attach itself to a host cell
• Disease


  • Illness/disorder of the body/mind that leads to poor health
  • Each disease is associated with a set of symptoms
• Infectious diseases


  Caused by pathogens and are transmissible (they can spread between individuals within a population)