1
Q
obtaining dna
A
- tissue sample is physically broken down in a buffer solution that includes salts a detergent to break down phospholipids in the membrane
- suspended particles, cell debris including organelles are separated from dna by a centrifugation
- the suspension contains the dna this is incubated with protease membrane at 37 degrees
- ice cold ethanol is added which causes the dna to precipitate out of the solution. then the dna is washed several times in a buffer solution to remove impurities
2
Q
creating fragments
A
- restriction enzymes are used to create dna fragments
- they are substarte specifc and will only cut dna at specific base sequences
if the restriction site at either side of the of str sequence, the fragment will remian intact - the same restrcition enzyme must be used for all the dna sample to ensure identical str fragments
3
Q
pcr (polymerase chain reaction)
A
- used to amplify dna
dna polymerase (heat soluble) - free dna mononucleotides
- dna primers ( to prevent unwanted dna from being amplified)
a series of heats are used - 95 degrees - this denatures the dna, it breaks the hydrogen bonds between the bases and seoerates the strand
- 55 - the optimal temperature for the uncalling of the primers
- 70 - optimal temperature for the dna polymerase and then the cycle is repeated
4
Q
seperating the smaples (gel electrophoresis)
A
- the dna samples are loaded into the wells at the cathod (-)
- because dna is negatively charged it will move to the anode (+)
- the sample migrates through the gel and seperates according to size
- ethidium bromide is attached (tracker dye)
- the gel is submerged in a buffer with a potential difference
- the smaller fragments migrate further through the gel and are closer to the anode
5
Q
time of death ( temperature )
A
- all metabollic reactions produce heat so they the normal body temperature is 37
- at the time of death the metabollic reactions stop, so the body temperature will stop and equal the temperature of the surrounds (ambient temperature)
- different factors can affect the rate of this such as clothing, weight, activity before death
6
Q
time of death rigor mortis
A
- muscles are deprived of oxygen
- anaerobic respiration then begins to takes place producing lactic acid
- decreasing the ph of the cells stopping the cells from producing atp
- no atp means the bonds between actin and myosin in the muscle cells becomes fixed and the muscles stiffen
- rigor mortis occurs faster in smaller muscles
7
Q
forensic entomology
A
- take samples of insects found near the body, where and when they were found
- the temperature of the air and body, and the maggot mass are measured
- ## this allows the determination of the rate of maggot development
8
Q
time of death ( stage of succession)
A
- after time of death the body conditions is very favourable for bacteria
- as bacteria decomposes tissue, conditions of the dead body become favourable for flies and their larvea
- when the fly larvea feed on dead body they make the conditions favourable for beetles, so the beetles move in
- as the body dries out the conditions become less favourable for flies so they leave and the beetles remain and decompose the dry tissue
- when there is no tissue it is not favourable for anything
9
Q
stages of decomposition
A
immediately after
- the heart stops beating, body cells become deprives of oxygen anaerobic respiration occurs, ph changes
- cells lose structural integrity gradually and break down, releasing their cellular enzymes which breaks down the cells and tissues in a process called autolysis
- putrefaction - the greenish discolouration of due to the formation of sulfhemoglobin
- due to the actions of bacteria it causes gases such as ammonia, methane to be produced and this will cause the body to smell and bloat,
- when the tissue further decomposes it will release these gases and the liquids associated with putrefaction and the body will deflate
10
Q
barriers to infection (skin flora)
A
skin flora
- the skins keratin outer layer is effective in stopping the entry of pathogens.
- pathogens can enter through wounds but, blood clotting seals it and stops the entry
- skin flora lives on the surface of the skin, these prevent the colonisation of bacteria
- other bacteria that are not suited to the conditioned created by salty sweat and excereted chemicals such as urea and fatty acids
11
Q
mucus membrane
A
- the mucus membrane that lines tha airwys an the gut provide easier routes into the body because of lacking keratin layer
- the surface is always moist, making it favourable for bacteria growth
- but the entry is limited by the action of mucus and cillia
- secrection in the mouth, eyes and nose contain lysozyme this enzyme breaks down the bacteria cell wall
12
Q
gut flora
A
- bacteria are found in the large and smnall intenstine
- these natural flora benefit because the conditions are suitable for the bacteria
- the bacteria secretes lactic acid and vitamin k
- preventing the colonisation of pathogens in the large intestine
13
Q
interferon
A
- produced in response to viral infection
- produced by virally infected cells ( transcriptor factors switch on the gene that codes for interferon)
- it diffuses to surround cells where it prevents viruses from multiplying
- inhibiting viral protein synthesis
interferon is secreted out of the cell by exocytosis
through secretory vesicles.
14
Q
inflammation
A
- damaged whit blood cells and mast cells release histamine
- histamine results in the dilation of the arterioles
- this increases in blood flow to the sight of the infection
- the histamine also increases the permeability of the capillaries
- plasma, white blood cells and antibodies pass through the walls of the capillaries into the tissue resulting in swelling
15
Q
lysozyme
A
this is the enzyme found in tears helps to fight bacteria
- it catalyses the hydrolysis reaction, breaking the glycosidic bonds in the peptidylglycine cell wall of the bacteria,
- causing the permeability of the cell wall to increase
- this affects the osmotic pressure, the cell wall has now weakened and water has entered by osmosis
- then the bacterial cells swell and burst.
16
Q
phagocytosis.
A
- pathogen is recognised as foreign
- pathogen attaches to surface receptors
- engulfed by phagocyte by endocytosis to form phagosome
- lysosomes ( containing hydrolytic enzymes, lysozyme and protease) fuse to phagosome
- release of h2o2, hcl and free radicals into phagosome
- it is digested and released as harmless products
17
Q
strcuture of viruses
A
- a strand of either dna or rna
- they have lipid membrane from host cell (protein capsid)
- they do not have a cytoplasm
viruses replicate by taking over the transcription and translation of the cell
18
Q
structure of bacteria
A
- they store glycogen granules
- single loop of dna and plasmid
- memsosome - where respiration occurs
- peptidoglycan cell wall
19
Q
definition of infection
A
- infection occurs when pathogens cuch as bacteria or viruses evade barriers such as the skin and are inside the cells ( and tissues) of the body
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