SNAB TOPIC 6- INFECTION, IMMUNITY AND FORENSICS
- Created by: CiaraRedmond
- Created on: 11-11-13 09:32
INFECTION, IMMUNITY AND FORENSICS
6.1 Forensic investigations and analysis of DNA
Investigating time of death
ð Harder after 48 hours
ð Forensic evidence combined with witness and circumstantial evidence
ð At death, metabolic reactions slow and then stop
o Lowering body temperature
§ drops straight after death, plateaus and then drops to room temperature
§ outside the body cools fastest
§ body fat acts as insulation
Rigor mortis
ð Muscle calls have large stores of ATP and glycogen, so respire anaerobically for a time
o As they run out of ATP the fibres become contracted ad solid
ð Starts 2-4 hours after death, needs between 6-8 hours for full effect
ð Begins in the face and neck, progressing down the body
ð Depends on levels of ATP at the time of death and level of activity before death
ð Not permanent
o Lasts between 36 and 48 hours after death, but can be considerably longer
ð Muscles soften as enzymes break down tissue
ð As cells die and gut movement stops, catabolic enzymes break down walls of the gut then surrounding cells
ð As cells die from lack of oxygen, lysosomes rupture, releasing enzymes to break down cells
Stages of succession
ð Colonisers
o Anaerobic bacteria in the gut breed freely
ð Joined by flies
o Blowflies
§ Arrive in minutes
§ Attracted to moisture
§ Lay eggs, maggots hatch
§ Feed on tissues and turn into flies
ð Beetles lay eggs on the carcass
ð Parasitic wasps lay eggs
ð Body dries out so cheese flies and coffin flies move in
ð Strong chewing beetles eat away at muscles and connective tissues
ð Mites and moths feed on hair until dry bones are left
ð Speed varies
o Temperature
§ Warmer bodies have faster decay rates
o Exposure
Forensic entomology
ð Blowflies
o Lay eggs in corpses
§ In natural openings
o eggs, maggots and pupae are collects
§ species identified
· each species have different life cycle lengths
DNA and the genetic code
ð DNA
o Double helix structure
§ Nucleotide bases
· Adenine, thymine, cytosine and guanine
o Unique to every organism
ð Proteins are formed of amino acids
o Only 20 naturally occurring
o Joined together on the ribosomes
ð Triplet code
o 64 possible combinations
ð Non-overlapping
ð Degenerate
Transcription of the DNA molecule
ð DNA is copied to form mRNA
ð The breakdown of the hydrogen bonds between bases is catalysed by enzymes called DNA-directed RNA polymerase
ð Template strand provides the order of sequence of nucleotides in an RNA transcript
ð RNA polymerase joins many small nucleotide units together to form mRNA
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