Topic 6 Flashcards
6.1 How to determine the time of death of a mammal?
-extent of decomposition
-stage of succession
-forensic entomology
-body temperature
-degree of muscle contraction
Decomposition
- The breakdown of tissues after death due to microorganisms and enzyme activity
-Signs include -Putrefaction (green colouration of the skin), Gas/liquid blisters appearing on the skin, unpleasant odour and body bloating.
-The rate of decomposition can be affected by the availability of oxygen and the surrounding temperature.
-Slower at anaerobic conditions and lower temperatures and faster at aerobic conditions and higher temperatures.
Stage of Succession
-Refers to the change in types of organisms found in a habitat over time. (habitat = dead body)
-Bacteria will be found on the body directly after time of death. Flies will start laying eggs, larvae hatch and eat the soft tissue, Beatles start appearing.
-Flies and larvae prefer a wet/moisture-rich environment.
-No tissue remaining, conditions are no longer favourable for most organisms
-SOS will differ depending on where the body is located as the accessibility of insects and availability of oxygen will be affected eg…. Buried in soil, buried in a coffin, under water.
Body temperature
Respiration and other metabolic processes produce heat in living organisms.
When a person dies…
- metabolic reactions will come to an end
- body temperature drops until it reaches the temp of the surrounding environment (algor mortis)
- decreases by 1.5-2.0 degrees Celsius per hour
- Air temperature, surface area:volume ratio and presence of clothing will affect the rate at which the body heat is lost.
Degree of muscle contraction
Muscles start to contract about 4-6 hours after TOD leading to a general stiffening of the body (rigor mortis)
Happens between 12-18 hours - wears off between 24-36 hours after TOD
Rigor mortis
- Muscles receive no oxygen, respire anaerobically producing lactic acid.
- Lactic acid decreases the pH, denaturing the enzymes that produce ATP.
- Myosin heads cannot be released from the actin filaments locking the muscles in a contracted state leading to the body stiffening.
Rigor mortis begins in smaller muscles and ends in larger muscles.
Level of muscle development and temperature of the surroundings affect rigor mortis.
6.2 Know the role of micro - organisms in the decomposition of organic matter and the recycling of carbon.
- Dead plants and animals are broken down by microorganisms e.g. bacteria and fungi.
- Microorganism secrete enzymes which break large organic molecules into smaller molecules.
- These small molecules such as glucose can be broken down further during respiration.
- Micro organisms involved in decomposition produce methane CH4 and CO2 carbon dioxide released back into the atmosphere.
- Carbon dioxide can then be absorbed by green plants which can fix the carbon back into carbohydrates during photosynthesis.
6.3 Know how DNA profiling is used for identification and determining genetic relationships between organisms (plants and animals)
DNA PROFILE
- very useful in forensic science as it provides a way to identify individuals
- can be used to determine the genetic relationships between different organisms e.g.
—> paternity and maternity testing
—> ancestry kits
—> determining evolutionary relationships between different species.
6.4 Know how DNA can be amplified using the polymerase chain reaction (PCR)
PCR is a common molecular biology technique used in most applications of gene technology e.g.
- DNA profiling
- Genetic engineering
Produces many copies of a piece of DNA ; this can be referred to as DNA amplification.
1. Sample is taken and DNA is extracted.
2. Primers, DNA nucleotides and DNA are added. DENATURATION
3. Sample is raised to 90c to separate the DNA strands. (breaks the hydrogen bonds that hold the two DNA strands together) ANNEALING
4. Sample is lowered to 55c to allow the primers to bind - (primers can anneal to the ends of the single strands of DNA)
5. Sample is raised to 70c to allow DNA polymerase to replicate the strands. ELONGATION/EXTENSION
6. Repeats many times making millions of copies of a small sample of DNA
Each PCR cycle doubles the amount of DNA
The genetic relationship between these two species of grey tree frog has been studied using DNA profiling (DNA fingerprinting).
A small sample of DNA was taken from each species of grey tree frog. This DNA was amplified, fragmented and used to produce a DNA profile (DNA fingerprint) for each species.
Describe how a DNA profile was produced from this small sample of DNA? (6 marks)
- Multiple copies of DNA made
- Using PCR/polymerase chain reaction
- Use of primers/DNA polymerase/nucleotides, many repetitions
- restriction enzymes produce DNA fragments
- gel electrolysis
- load the DNA onto the gel (agar gel)
- electric current is applied
- use of fluorescent tag/UV light
How to compare DNA profiles? (3 marks)
- compare total numbers of bands
- compare position of bands
- comparing size/width of bands
Gel electrophoresis CORMS
• Multiply DNA using PCR
• Make fragments using restriction enzymes to cut the DNA at specific
sequences
• Pour buffer solution over the gel
• Add the DNA fragments and fluorescent markers to the sample wells using a pipette loading
• Apply a current across the gel
• DNA is negatively charged due to the phosphate in its backbone
• So moves towards the positive electrode
• Compare samples, more similarities indicate more closely related
EXAMPLE - A deer was found dead on National Trust land. Some people thought that the wounds that led to the deer’s death could have been caused by a big cat such as a black panther.
The DNA produced by PCR was analysed to find out if a black panther was involved.
Explain how gel electrophoresis could be used to find out if this DNA came from a black panther. (5 marks)
- detail of loading of electrophoresis tank e.g. use of agarose gel, use of a buffer, sample placed in wells.
- current/potential difference applied across the gel
- use of gene probe/DNA stain e.g. methylene blue.
- use of STRs/DNA of black panther
- compare bands/DNA profiles
- a match would indicate that DNA from a black panther was present.
How to create a DNA profile?
- isolating a sample of DNA e.g from saliva, skin, hair or blood.
- producing more copies of the DNA fragments in the sample using the polymerase chain reaction (PCR).
- The fragments are separated and visualised using gel electrophoresis.
What are DNA profiles and how can they be useful?
- Can be used to determine the genetic relationships between people e.g. in paternity tests
- Can be useful in selective or captive breeding programmes of animals or cultivation of plants.
- DNA profiles can be compared to determine relationships in paternity testing.
Devise an investigation to determine the optimum number of cycles for the polymerase chain reaction used to amplify the DNA for this test.
- DNA, polymerase, primers (appropriate reagent to be provided)
- Temperatures used are 90, 55 and 70.
- Change the number of cycles.
- Use gel electrophoresis to determine the quantity of DNA produced.
- Choose the smallest number of cycles that produces an observable band.
6.5 Be able to compare the structure of bacteria and viruses.
- Bacteria have DNA, Viruses have DNA and RNA.
- Bacteria have circular genetic material, Viruses have linear/straight.
- Bacterial DNA is double stranded, Viral DNA/RNA is single or double stranded
- Bacteria may have plasmids, Viruses do not.
6.6 Understand how Mycobacterium tuberculosis (TB) infect human cells, causing a sequence of symptoms that may result in death.
- Inhale Mycobacterium tuberculosis.
- Macrophages ingest the bacterium but cannot digest it due to the thick waxy layer.
- Tubercles form in response to the infection – immune system cells surrounded by a fibrous membrane.
- Some Mycobacterium tuberculosis may survive at the center of the tubercles & lie dormant for years.
- When the immune system is compromised the bacteria multiply rapidly and destroy the lung tissue.
- In too high numbers for the immune system to be able to cope.
- They may also travel in the blood to other organs and destroy those too.
The active TB bacteria can inhibit T-cells
T-helper aren’t activated to produce cytokines
So B-cells aren’t activated to produce antibodies
T-killer cells aren’t activated to kill infected cells
Weakened immune system leads to opportunistic infections.
6.6 Understand how Human Immunodeficiency virus (HIV) infects human cells, causing a sequence of symptoms that may result in death.
- Glycoproteins on the surface of the virus
- bind to the CD4 receptors on the surface of the T helper cells
- Viral envelope fuses with cell membrane of T helper cell
- Viral RNA enters the cell
HIV symptoms
- First symptoms - flu like including fevers, tiredness and headaches
- After several weeks HIV antibiotics appear in blood, thus making a person HIV positive
- After this, the symptoms disappear until the immune system becomes weakened again, thus leading to AIDS.
- Weight loss, diarrhoea, dementia, cancers and opportunistic infections such as TB. These opportunistic infections can lead to death.
6.7 Understand the non-specific responses of the body to infection including Inflammation, lysozyme action, interferon and phagocytosis. (Non - specific response)
Inflammation
Inflammation -
- Histamine is released
- causes arterioles to dilate/vasodilation
- which increases the blood flow (to the site causing redness)
- histamine also causes the permeability of capillaries to increase
- allowing blood plasma, white blood cells and antibodies to leave the capillary (enter the tissues) causing Edema/swelling and pain.
Lysozome action (Non - specific response)
Lysozyme is an enzyme found in secretions such as tears and mucus which kills bacterial cells by damaging their cell wall (causing lysis)
Interferon (Non specific response)
- When cells are invaded by viruses they produce a group of chemicals called interferon’s.
- An interferon diffuses from the cell where it is made into the surrounding cells.
- It then binds to receptors in the surface membrane of uninfected cells.
- This stimulates a pathway which makes the cells resistant to infection by viruses by stopping them reproducing.
- This prevents the infection of more cells when the virus breaks out of the first cell.
