Unit 6: Forensics Flashcards
What is the extent of decomposition?
Bodies following a pattern of decay and decomposition. This usually starts with enzymes from the digestive system breaking down the surrounding tissue, while cells release enzymes as they begin to break down. Stages of decomposition is used to determine how long a body has been dead for.
What is forensic entomology?
It is the study of insects used to determine the time of death. Each species has a specific life cycle. Determining the age of the insect present enables the the time of death to be determined.
What is the stages of succession?
As the body decays, the species colonising the body change. Therefore, the analysis of the community of species present can be used to determine the time of death.
How is body temperature used in forensics?
The temperature of the body begins to decrease after death as heat-producing metabolic reactions stop. However, temperature can only be used to determine the time of death in the first 24 hours. Equals the surroundings (algor mortis)
How is the degree of muscle contraction used in forensics?
After deaths muscles begin to stiffen as ATP is used up, calcium ions build up in the muscle and become fixed in a state of contraction (rigor mortis). The extent of rigor mortis can be used to determine the time of death. Begin after 2-4 hours of death and lasts to 36 hours so limited in use in determining the time of death.
How does microorganisms such as bacteria and fungi play an important role in the decomposition of organic matter and the recycling of carbon?
Bacteria and fungi secrete enzymes that decompose organic matter into small molecules which they then use as respiratory substrate - carbon dioxide and methane are released in the process, thus recycling carbon.
How do microorganisms decompose organic matter?
Microorganisms (bacteria and fungi) are important to the carbon cycle. When they die they secret enzymes that decompose the dead organic matter into small molecules that they can respire. Methane (CH4) are released. This recycles carbon back into the atmosphere.
What is DNA profiling?
It is a genetic fingerprint of an organisms DNA. It is unique to you. Used to identify people and determine genetic relationships
What are the different stages of obtaining a DNA sample to then use in gel electrophoresis?
1) DNA sample obtained (blood, saliva)
2) PCR used to amplify DNA
3) Fluorescent tag is added (stain)
4) Gel electrophoresis is used to separate the DNA
5) Gel is viewed under UV light (compare band patters- determine genetic relationship)
What is the process if PCR?
1) Reaction mixture contains DNA sample, free nucleotides, primers and DNA polymerase. Primers- short pieces of DNA are complementary to the bases at the start of the fragment you want. DNA polymerase- enzyme, creates new strand of DNA.
2) DNA mixtures heated at 95°C- break hydrogen bonds
3) Cooled between 50-65°C - primers bind to the strand
4) Heated 72°C so DNA polymerase can work
5) DNA polymerase lines up the free DNA nucleotides alongside the template strand- complementary base pairings means new complementary strands
6) Two new copies of the fragment of DNA are formed and one cycle of PCR is complete
7) Cycle starts again- heated 95°C all four strand (2new and 2 original) are used as templates
8) Each PCR cycle doubles the amount of DNA e.g. 1st cycle= 2 x 2 = 4 DNA fragments
What is the process of gel electrophoresis?
1) DNA placed into a slab of gel and covered with a buffer solution that conduct electricity
2) Electrical current passes through the gel. DNA fragments are negatively charged, so they move towards the anode (positive electrode) - far end of gel
3) Short DNA fragments move faster and travel further through the gel, so the DNA fragments separate according to length.
How is DNA profiling used?
DNA is isolated and each sample is amplified using PCR and the products are run on electrophoresis gel and the DNA profiles produced are compared to see if there are any match. If so, it links the person to a crime scene, for example.
How is DNA profiling used to determine genetic relationships in humans
Inherit DNA from our parents, roughly half from each. More bands on two DNA profiles that match, the more closely-related they are (genetically similar). For example, paternity tests used to determine the biological father.
How can DNA profiling be used in animals and plants?
Used to prevent inbreeding (causes health, productivity, and reproductive problems) on animals and plants. Inbreeding decreases the gene pool (number of different alleles)- increase risk of genetic disorders. Used to identify closely related individuals and the less related individuals are bred together.
How to carry out gel electrophoresis (gel tray)
1) Use an agarose gel poured into the gel tray and left to solidify. A row of wells is created at one end of the gel.
2) Put gel tray into the gel box/tank. End of gel tray with the wells closest to the cathode (negative electrode)
3) Add buffer solution to the reservoirs at the sides of the gel box so that the surface of the gel becomes covered in the buffer solution.
How to carry out gel electrophoresis (DNA samples)
1) Fragmented DNA sample using a micropipette, add the same volume of loading dye (helps samples to sink to the bottom of the wells, so they are easier to see).
2) Add set volume (e.g. 10µl) of DNA sample to the first well. Really carefully- use the tip of the micropipette is in the buffer solution and just above the opening of the well. Not too far in as it will pierce the bottom.
3) Repeat for other DNA samples- clean micropipette tip each time.
4) Record DNA samples added to each well.
How is the electrophoresis carried out?
1) Put the lid on and connect leads to power supply
2)Turn on and set to required voltage. Causes an electrical current to pass through the gel
3) Current will separate the DNA fragments according to length
4) Run for 20 mins (or until the dye is about 2cm from the end of the gel) and then turn of the power supply
5) Remove the gel tray from the gel box and the tip off any excess buffer
6) Wearing gloves, stain the DNA fragments by covering the surface of the gel with a staining solution, then rinsing the gel with water. Bands of different DNA fragments will now be visible.
What is the structure of bacteria?
Single-celled prokaryotic, no nucleus, only a few micrometres. They have plasma membrane (cell membrane, may contain folds called mesosomes), cytoplasm, ribosome (produce proteins from mRNA), flagellum (tail- make the bacteria move), cell wall (support- made of glycoproteins made of murein, capsule (secreted slime, protect from attacks), Plasmids (small loops of DNA), bacterial chromosomes (DNA floats free in the cytoplasm), pili (hair-like structure, help bacteria stick together and can be used in gene transfer)
What is the structure of a virus?
Microorganism but they are not cells, just nucleic acid surrounded by protein. Smaller than bacteria. No plasma membrane, no cytoplasm, no ribosome. Contain core of nucleic acid that’s either DNA or RNA (HIV it’s RNA). Protein coat around the core is the called the plasmid. Some viruses have an extra outer layer (envelope), stolen from the cell membrane of a previous host cell. Attachment proteins stick out from the edge of the capsid/envelope- cling onto suitable host cell. Some viruses carry proteins inside their capsid, e.g. HIV carries an enzyme called reverse transcriptase.
How does pathogens cause infectious disease?
Pathogen is any organism that causes disease- infectious disease. Include some bacteria, fungi and viruses. Disease develops in an organism it causes a sequence of symptoms, which may lead to death.
What is HIV?
Human Immunodeficiency Virus (HIV)
Why does HIV relpicate?
It replicates inside its Host’s T helper cells. It is spread through infected bodily fluids. Come into contact with mucosal surfaces or damaged tissue or injected in to the bloodstream. Common way through sexual intercourse. Cam only reproduce inside the cells. HIV replicates inside the T helper cells (doesn’t have enzymes or ribosomes to replicate on their own).
How does HIV replicate?
Attachment proteins attach to a receptor molecule on the cell membrane of the T helper cell. Capsid released into the cell, uncoats and releases genetic material into the cells cytoplasm. Reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template. Double strand of DNA is made and inserted into the human DNA. Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA. The viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells.
How does HIV cause AIDS?
Leads to acquired immune deficiency syndrome (AIDS). Immune system deteriorates and eventually fails. Classed as having AIDS when symptoms of their failing immune system start to appear or their T helper cell count drops. Opportunistic infection is when people with AIDS wouldn’t cause serious problem in people with a healthy immune system. Length of time between infection with HIV and the development of AIDS varies between individuals but without treatment around 10 years.
How does AIDS progress?
The initial symptoms of AIDS include minor infections of mucous membranes. Caused by a lower than normal number of T helper cells. Progresses as number of T helper cells decreases, more suspectable to serious infection. Late on, very low number of T helper cells and suffer from a range of serious infections (such as toxoplasmosis- parasite infection). Serious infection kills AIDS patients, not HIV itself.
What bacteria causes TB?
Bacterium Mycobacterium tuberculosis
