Topic 6- Forensics and Microorganisms + Immunity Flashcards
1
Q
What are the 5 ways to determine TOD
A
- Core Body Temp
- Degree of Muscle Contraction/ Rigor Mortis
- Forensic Entomology
- Extent of Decomposition
- Stage of Succession
2
Q
Describe how to determine TOD from core body temp.
A
- all mammals produce heat from exothermic metabolic reactions (human body 3ºC)
- from TOD metabolic reactions slow down until stop = body temp. falls until reaches ambient temp. (ALGOR MORTIS)
- scientists know rate at which body cools so can find TOD by comparing body temp. w/ living body temp.
Factors: - air temp, body weight, clothing affects cooling rate
3
Q
Describe how to determine TOD from degree of muscle contraction
A
- 4-6 hrs after death, body begins contraction + becomes stiff = rigor mortis
1. begins when muscle cells are deprived of O2
2. anaerobic respiration takes place causing a build up of lactic acid in the muscle
3. the low pH of the cells due to the lactic acid, inhibits enzymes producing ATP
4. no ATP causes bonds between myosin and actin in muscle cells to become fixed = body stiffens
5. Complete stiffening takes around 12-18 hrs
Factors: - occurs more quickly at higher temperatures (chemical reactions are faster)
- smaller muscles contract first
4
Q
Describe how to determine TOD with forensic entomology
A
- study of the body being colonised by different insects
1. identify type of insect on body e.g flies appear a few hours after death and beetles colonise later
2. estimate using stage of life cycle insects are in e.g blowfly larvae hatch from eggs around a day after laid
- if eggs found, TOD was no more than 24hrs ago
Factors:
- drugs, humidity, O2 and temperature
- e.g higher temp = faster metabolic rate and shorter lifecycle
5
Q
Describe how to determine TOD using the Extent of Decomposition
A
- immediately after death microorganisms decompose the body (bacteria)
- microorganisms secrete enzymes that decompose dead organic matter into small molecules they can respire (respiration releases CO2)
1. hours to few days= cells + tissues broken down by bacteria present before death/ skin turns greenish
2. few days-few weeks= microorganisms decompose tissues + organs producing gases (methane) to cause bloating of body/ skin blisters and falls off
3. few weeks= tissues liquify and seep into area around body
4. few months- few years= only skeleton
5. decades-centuries= skeleton disintegrates until nothing left
Factors:
- rate affected by temperature and O2 availability as microorganisms are aerobic
6
Q
Describe how to determine TOD using Stage of Succession
A
- types of organisms on body change over time
If dead body above ground:
1. After TOD, bacteria decomposes tissues and conditions become more favourable for flies + larvae
2. fly larvae feed on dead body + make conditions favourable for beetles
3. dead body dries out so conditions are less favourable for flies and they leave/ beetles remain and decompose dry tissue
4. when no tissue, not favourable for any organism
** similar to plant succession but most of the earlier insects remain as other insects colonise
Affected by location (if sealed away, no colonisation)
7
Q
What are the steps in DNA profiling?
A
- obtain DNA sample from organism you are profiling (from blood, saliva etc)
- PCR (polymerase chain reaction) to amplify DNA
- Add fluorescent tag to be viewed under UV light
- Separate DNA wi/ gel electrophoresis
- View gel and fragments under UV light
- Compare samples of DNA from crime scenes to see what people are linked to the crime if the suspect’s DNA matches
8
Q
Describe PCR
A
- makes millions of copies of specific regions of the DNA as DNA must be amplified to make a DNA profile
1. reaction mixture contains:
- DNA sample
- primers= short sections of DNA complementary to bases at start of fragment (shows where DNA polymerase has to bind)
- free nucleotides= construct new DNA/RNA
- buffer solution= optimum pH for reaction
- DNA polymerase= builds new strands
2. Denaturation= mixture heated to 95ºc to break H bonds between 2 strands of DNA
3. Annealing= Mixture cooled to between 50-60ºc so primers can anneal to ends of single DNA strands
4. Elongation= temp. increased to 72ºc as it is optimum temp for DNA polymerase to build complementary strands of DNA
5. Cycle repeats again at 95ºc and DNA doubles per cycle
9
Q
How does electrophoresis work?
A
- amplified DNA is treated w/ restriction enzymes and fluoresent tag
- restriction enzyme breaks DNA into fragments of different length (cut between short tandem repeats)
- fluorescent tag allows fragments to be viewed under - fragments iserted into a well at end of piece of agar gel + current is passed through
- buffer solution conducts electricity and DNA fragments are negative so move toward anode at far end of gel - short DNA fragments move faster and travel further through gel (fragments separate by length)
- diff. individuals will have diff. DNA fragments and therefore, banding patterns
10
Q
Describe electrophoresis CP
A
- cut wells in agarose gel and add buffer solution
- pipette DNA samples into wells using micropipette with a standard of known results to compare
- -ve electrode to the end of the plate w/ the wells so fragments move to anode (max. 45V)
- let gel run for 30 minutes and turn off
- stain fragments w/ staining solution + rinse w/ water
- bands will be visible
- wear gloves
11
Q
How are DNA profiles used in paternity tests?
A
- we inherit DNA from our parents/ around half comes from each parent
- more band on the 2 DNA profiles match = more genetically similar/ closely related
12
Q
How can DNA profiling be used to prevent inbreeding?
A
- inbreeding decreases gene pool causing the increased risk of accumulation of harmful recessive alleles
- DNA profiling can identify how closely related individuals are and less related individuals will be bred together
13
Q
Describe the structure of viruses.
A
- microorganisms and not cells w/ no plasma membrane, cytoplasm or ribosome
- contain a core of nucleic acid that’s either DNA/RNA
- surrounded by a protein coat = capsid
- some have extra outer layer stolen from cell membrane of a previous host cell = envelope
- attachment proteins stick out from capsid/ envelope = so virus can cling to host cell
- some carry proteins inside capsid = like reverse transcriptase in HIV
14
Q
What is HIV and how is it spread?
A
- human immunodeficiency virus that infects + destroys T helper cells
- spread through bodily fluids (sharing of needles/ intercourse)
- it can only reproduce inside cells of the organism it infects as it doesn’t have enzymes and ribosomes to replicate on its own
15
Q
Describe how HIV replicates
A
- HIV infects T helper cell by attaching its gp120 attachment protein to CD4 receptors on the cell’s membrane
- virus envelope fuses w/ helper cell membrane + viral RNA enters
- inside host cell, HIV uses reverse transcriptase to manufacture DNA from its viral RNA template = HIV DNA strand produced
- DNA integrates w/ host’s DNA by integrase which is transcribed + translated = produced viral proteins which are assembled into new viruses
- they leave T-cell + take some of host cell’s membrane, killing the cell
16
Q
Describe the changes during initial infection of HIV to the latency period.
A
- after initital infection, HIV replicates rapidly (flu like)
- latency period = when HIV replication drops and the infected person doesn’t experience symptoms
- due to decrease in T-Helper cells, B cells aren’t activated + no antibodies produced after latency period
17
Q
How does HIV lead to AIDS
A
- AIDS = aquired immune defeciency syndrome
- when T-helper cell count drops below certain level / symptoms of immune system failing
- as AIDS progresses, no. T-helper cells decreases further = more susceptible to more serious infections increased risk of opportunistic infections
- infections will become more and more serious as there are fewer immune system cells to fight them off
18
Q
What are the factors that affect survival time w/ AIDS?
A
- existing infections
- the strain of HIV infected with
- age
- access to healthcare
19
Q
What is TB and how is it transmitted?
A
- bacterial infection caused by Myobacterium tuberculosis
- when tiny droplets containing bacteria (from cough/sneeze) inhaled into lungs
- spreads very quickly in overcrowded conditions
20
Q
Describe how TB infects a person.
A
- once in lungs tehy are engulfed by phagocytes during phagocytosis
- may survive + reproduce inside phagocytic vacuole - over time, infected phagocytes become encased in tubercules in lungs where bacteria stays dormant (show no syptoms)
- Later on, dormant bacteria may be reactivated and overcome the immune system if no. bacteria is too high = active TB
- more likely to be reactivated if immune system is compromised by AIDS etc. - multiply rapidly + destroy lung tissue = holes + cavities
21
Q
Describe the sequence of symptoms developed by TB
A
- initial symptoms are fever, general weakness + severe coughing caused by inflammation of lungs
- As TB progresses, damages lungs and can cause respiritory failure if not treated/ death
- can also spread to other parts of body e.g brain + kidneys and can then cause organ failure
22
Q
What are the barriers to infection?
A
- stomach acid = if eat/ drink pathogens they are killed by acidic conditions of stomach
- skin= physical barrier to pathogens but if damaged, pathogens ojm surface can enter bloodsteam
- blood clots at area prevent some pathogens entering - gut + skin flora = intestines + skin are naturally covered in billions of harmless microorganisms that compete w/ pathogens for space + nutrients (harder for them to infect)
- lysozymes= mucosal surfaces produce secretions containing lysozyme enzyme killing bacteria by damaging cell walls = burst (lyse)
