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DNA Extraction and Amplification
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a lab report on how to extract DNA
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Lab reportAbstract
This experiment was carried out to understand the process of extracting DNA because in the world
of forensic science, DNA profiling is relied on because it can help the conviction of a suspect, which
is essential in a fair justice system and can decrease the risk of arresting innocent people who were
most likely at the wrong place at the wrong time. In order to collect enough DNA to analyse, it
needs to be extracted, amplified and analysed. This experiment focussed on extracting DNA from a
non-organic source and was done through adding an extraction solution made of detergent, salt
and water to a cut up kiwi which was then mashed up and left for 20 minutes, it was then filtered
to get rid of any seeds that was already in the fruit. The next step was to add pineapple juice and it
was left for another five minutes and finally, pure ethanol was added, and it was then left for 10
minutes which left a gap in the beaker that was used. The findings of this experiment were that
there was direct partition in the kiwi-extraction-ethanol solution, meaning that the experiment was
a success as DNA had been extracted.
Introduction
DNA needs to be extracted in a forensic science context because in the modern world of forensic
science, we rely on DNA profiling which is a technique used in the justice system to use DNA
evidence in the conviction of a suspect which is used to prevent from innocent people from being
falsely convicted. And in order to extract enough DNA that can be used in court , it needs to be
amplified which is the process used to produce multiple copies of DNA and has a specific step by
step process that has to be followed correctly to get the copies. There are changes in temperature
and reagents that are important for copying. PCR is used to amplify the DNA. When approaching a
crime scene, there are common sources of DNA that are found at most scenes. These are blood,
semen, urine, saliva, hair, teeth and bones and tissue. Blood is one of the more useful sources of
evidence to find at a crime scene because it contains a lot of human DNA but isn’t attained from
the blood cells because there is and is found in the white blood cells and this can be very good in
extracting DNA as it has pure DNA in the white blood cells. PCR or polymerase chain reaction
analysis is used to analyse the blood and has withstood court challenges on its validity. Another
sample that is commonly used in forensic investigation is semen which is another highly successful
sample because it has six times more DNA that is compact than normal cells, meaning that it has a
high concentration in DNA, and it can be amplified without the sperm cells dying as they can live up
to five days after ejaculation under the perfect conditions . The third type of source is saliva and
although it does have a lot of DNA and can be used in drug tests, it’s not commonly found at crime
scenes because it can’t be easily identified because there’s no distinct colour. Another source is
urine which isn’t used often in forensic investigations because it’s a waste product and it has
multiple sources of DNA that can be contaminated by other cells in the body. This would mean that
the extraction and amplification techniques wouldn’t be as reliable because there isn’t much DNA
to complete the process and urine tends to be low in nucleated cells, meaning that the
concentration and quality of DNA would be low. The fourth type of source is hair without the root
and although DNA can be only found at the root, its sometimes possible to extract from the
nucleated corneocytes. However, hair goes under a self-destruction sequence once it is no longer
attached to a living body so there is a race against time to use the hair sample that was found at the
crime scene. The fifth type of source is bone and teeth, and this source is useful because not all
investigations are conducted at the scene of the crime because it takes a while for evidence to be
evidence and when this happens, sources of DNA that can last over time is relied on. Bone is perfect
for this as it has a half-life of 521 years and under perfect conditions, it would take 6.8 million years.
, The DNA from teeth is found in the pulp and cementum. The sixth type of source is tissue which can
be identified through mRNA profiling and tissues such as skin contain special proteins that can
identify a particular sample. This may not as reliable due to the decomposition of the tissue after is
no longer a living body.
Non-organic extraction method
Equipment list-
- Water - Measuring cylinder
- Table salt - Paper towels
- 2 teaspoons of detergent - Stirring rod
- Ethanol - Fork
- Pineapple juice - Knife
- 2 kiwis - Teaspoon
- 2 small glass beakers - Chopping board
- Sieve - Bowl
Method
1. Collect cells
- The kiwi needs to be broken up so that the extraction solution can access the cells
- To do this, use a knife and chopping board to peel and chop the kiwi into small
chunks
- Transfer the chunks into a small beaker, using the fork to mash up the kiwi
2. Release DNA from cells
- In another beaker, mix 80ml of water , 1tsp of table salt and 2tsp of detergent
together
- Stir to combine the components, making sure that it’s stirred slowly to stop bubbles
from forming
- The detergents hydrophilic head allows it to dissolve in water during which its
hydrophobic tail attracts and breaks down the lipids that make up the cell membrane
and nuclear envelope, which holds the DNA
- The ionic strength can be increased with the addition of the salt, causing the proteins
to become insoluble and clumps together.
3. Separate DNA from proteins& other cellular contaminants
- Filter the solution using damp paper towels and a sieve into the bowl which will
separate the seeds and large chunks
- The histone proteins that the DNA is wound around is still present
- Add 1ml of pineapple juice for every 5ml of solution- the enzymes in the pineapple
juice will break down these proteins.
- Pour the solution into the measuring cylinder
4. Isolate the concentrated DNA (alcohol precipitation)
- DNA is soluble in water because it is a polar molecule due to its negatively charged
phosphate groups that is on the sugar-phosphate backbone, making DNA
hydrophilic.
- However, DNA is insoluble in alcohol because it is a non-polar solution
- Add cold ethanol at a 1:1 ratio and leave for 10 minutes
- The DNA will form a layer at the top of the measuring cylinder
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