Topic 6 Flashcards
How does body temperature determine time of death?
Body Temperature (algor mortis)
- Mammals produce heat from metabolic reactions
- From TOD metabolic reactions slow down and eventually stop
- Body temp falls to temp. of surroundings = algor mortis
- Human bodies cool at a rate of 1.5-2C per hour
- Air temp, clothing and body weight affects cooling rate
How does Muscle Contraction determine time of death?
Muscle contraction (rigor mortis)
- After 4-6 hours muscles in the dead body start to contract and become stiff
- Occurs when muscle cells become deprived of O2
- Anaerobic respiration occurs = build up of lactic acid
- pH of cells ↓ = ATP-producing enzymes inhibited
- No ATP = bonds b/w myosin and actin can’t detach
- Smaller muscles in the head contract first
- Occurs quicker at higher temperatures
How does Forensic Entomology determine time of death?
Forensic Entomology
- Body is colonised by dif. insects
- TOD estimated by the type/s of insects on the body
- Flies are first (a few hours after)
- TOD estimated by the stage of life cycle the insect is in
- Blowfly larvae hatch 24 hours after being laid
- Drugs, humidity, O2 and temp. affects life cycles
What is decomposition?
Decomposition = Immediately, bacteria and enzymes begin to decompose the body
Extent of decomposition - Hours→few days
Cells and tissues broken down by the body’s enzymes and bacteria. Skin begins to turn green.
Extent of decomposition - Few days→few weeks
Microorganisms decompose tissues and organs = gases = bloated body. Skin begins to blister and fall off.
Extent of decomposition - Few weeks
Tissues begin to liquefy and seep into the surrounding area.
Extent of decomposition - Few months→few years
Only a skeleton remains
Extent of decomposition - Decades→centuries
Skeleton begins to disintegrate into nothing
What is decomposition affected by?
- Affected by temp. and O2 availability
Stage of succession
- Type of organism in a dead body changes over time = succession
- TOD estimates from the stage of succession
- Immediately conditions ideal for bacteria, which decompose tissues
- Conditions then ideal for flies and larvae, which feed on the body
- Conditions then ideal for beetles
- Body dries out, flies leave, beetles stay to decompose dry tissue
- When no tissue remains, conditions ideal for almost nothing
- Similar to plant succession but pioneer species generally remain
- Affected by location, and lots of other things
What is the role of microorganisms?
They decompose organic matter
- Inc. organisms such as bacteria and fungi
- Important to C cycle
When on/ in a dead organism
- They secrete enzymes to decompose dead organic matter
- Turns it into small molecules they can respire
- CH4 (methane) and CO2 are released
- Recycles C back into the atmosphere
What is a DNA profile?
DNA profile = genetic fingerprint
- Everyone’s is diff. except for identical twins
- Fingers are coated in oil from sebaceous glands = prints
- Can find prints using aluminium or magnetic powder, or a Ninhydrin spray
How do you conduct a DNA profile?
- Obtain DNA sample
- PCR amplifies the DNA
- Fluorescent Tag is added
- To view the DNA under UV light - Gel Electrophoresis
- Gel is viewed under UV light
- DNA fragments appear as bands under the light = DNA profile
- Profiles can be compared by looking for similar patterns
How are DNA profiles conducted in Forensic Science?
Can be used in Forensic Science
- DNA collected from crime scenes and then suspects
1. DNA is isolated from all collected samples
Each sample is amplified
2. PCR products run on an electrophoresis gel
3. DNA is compared to look for matches
4. Matching samples link the person to the crime scene
How are DNA profiles used in determining genetic relationships?
In humans
- Inherit ~50% of DNA from each parent
∴ more matching bands = more closely related
In plants and animals
- Prevents inbreeding avoiding health, productivity and reproductive problems
- Inbreeding = ↓ gene pool (no. of dif. alleles)
- ↑ risk of genetic disorders and then health problems
- More similar DNA profiles = more closely related
What is DNA amplification?
Done using Polymerase Chain Reaction (PCR)
- Makes millions of copies of specific regions of DNA
- Used to make sure there’s enough to make a DNA profile
How is PCR conducted?
- Reaction mixture is set up
- DNA sample, free nucleotides, primers and Taq polymerase
- Primers = short pieces of DNA complementary to bases at start of wanted fragment
- DNA polymerase = enzyme that creates new strands - Heat mixture
- Heat to 95°C
- Break H bonds b/w the two strands of DNA (DNA helicase) - Cool mixture
- Cool to b/w 50 and 65°C
- Primers can bind/ anneal to the strands - Heat mixture
- Heat to 72°C
- Taq polymerase can then work - Taq polymerase gets to work
- Lines up free DNA nucleotides alongside template strand
- Complementary base pairing = complementary strand formed - Cycle complete
- 2 new copies of DNA have been made
- The cycle starts again from stage 2
- Both strands act as template strands
- Each cycle doubles the amount of DNA
How to conduct Gel Electrophoresis?
- Gel Tray set up
- Solidified Agarose gel in a gel tray w/ a row of wells at one end - Gel Box set up
- End w/ the wells closest to the cathode (-ve electrode) (cats are always -ve)
- Add buffer solution to reservoirs at side of gel tray so surface of gel is covered - Add dye
- Add the same vol. of loading dye into each fragmented DNA sample
- Helps DNA sink to the bottom of the wells and easier to see - Add DNA
- Add set vol. of a DNA sample into a well
- Make sure tip of micropipette is in buffer solution but above the opening of the well
- Don’t pierce the bottom of the well
- Repeat for each DNA sample into each well w/ clean micropipettes - Power Supply set up
- Place lid on gel box
- Connect leads from gel box to power supply
- Turn the power on and set to the required voltage
- Causes an electrical current to pass through the gel
∴ DNA fragments will separate according to length
- Leave for ~30 mins or till dye is ~2cm from end of gel - Staining the DNA
- Remove gel tray from the gel box
- Tip off any excess buffer solution
- Cover surface of the gel w/ staining solution to stain the gel
- Rinse the gel w/ water and DNA fragments will be visible
- DNA = southern blotting
- Protein = western blotting
- RNA = northern blotting
What are bacteria?
Bacteria
- Single-celled, prokaryotic microorganisms (no nucleus)
- Generally only a few micrometers long
What are viruses?
- Micro-organisms but aren’t cells
- Are just nucleic acids surrounded by protein
- Smaller than bacteria so less than 1 micrometre long
What is HIV?
Human Immunodeficiency Virus = HIV
- Spread through infected bodily fluids touching mucosal surfaces or damaged tissues
- Most common transfer is sexual intercourse
- HIV can only reproduce inside infected cells, T helper cells
- It doesn’t have its own equipment, eg. enzymes or ribosomes
- Initial infection period = fast replication = severe flu-like symptoms
- Then HIV replication ↓ = latency period = no symptoms
How to replicate HIV?
- Attachment proteins attach to receptor molecules on cell membrane of T helper cells
- The capsid is released into the cell
- It uncoats and releases the genetic material
(RNA) into the cell cytoplasm
- It uncoats and releases the genetic material
- Reverse transcriptase makes a complementary strand of DNA from the viral RNA template
- Then double-stranded DNA can be made and inserted into the human DNA
- Host cell enzymes used to make viral proteins from the viral DNA in the human DNA
- Viral proteins are assembled into new viruses
- The new viruses bud from the cell and infect other cells
How does HIV turn to AIDS?
- Initial symptoms = minor infections of mucous membranes and recurring respiratory infections
E.g nose, ears and genitals
2. T helper cell no.s continue to ↓ = more susceptible to more serious infections
E.g chronic diarrhoea, severe bacterial infections and TB
3. Late stages = v. low no. of T helper cells = range of serious infections
E.g toxoplasmosis of the brain (parasite), candidiasis of respiratory systems (fungal)
Patient will die from these serious infections not AIDS
How to treat HIV?
Antiretroviral therapy = combination of drugs everyday
- Doesn’t cure HIV but ↑ life expectancy
- ↓ viral load = ↓ risk of transmission
- Prevents HIV from multiplying
- Reverse transcriptase inhibitors = prevent viral RNA from making DNA
- Protease inhibitors = inhibits proteases
- Proteases cut larger proteins into smaller polypeptides
