DIY DNA extraction - a tool for
AgResearch New Zealand has used our technique in
classrooms across the nation ...a great techniques fo ramateur
Find out how to extract your own human DNA
(featured in the New Zealand Science Teacher
journal, No 103, 2003. ISSN 0110-7801)
If someone gave you some salt, flour,
citric acid, icing sugar, milk powder, baking soda, and fruit drink
powder from the kitchen, would you know how to make Sherbet? Simply
mixing all these ingredients together will produce nothing but a sticky
You can't make something useful without a
recipe, just like you can't build a living thing without a plan. If you
are feeling hungry, have a break using the
DNA - THE RECIPE FOR LIFE:
Back to our lesson...think of a whole
organism such as yourself...what makes you human? You, a human, can be
thought of as being made up of smaller pieces...a number of different organs.
Some of your organs are the brain,
skin, the liver, kidneys, muscles, etc So what are organs made up of? Specialised
Muscles are made up of muscle cells,
the skin is made up of skin cells, and so on. How does a skin cell know
how to be a skin cell? It has a set of instructions of how to be one,
instructions stored on chromosomes.
A human will never really have
kittens because we don't have the instructions of how to make cat
cells! A seed knows what type of plant it should look like because it
has the set of instructions to make all the organs (leaves, roots, etc)
it requires to look like the parent plant.
The plan is stored on thread-like
chromosomes, made of a chemical called DNA. We can get the DNA
plan out of cells and study it, change it or swap it!
To isolate plant DNA
- blend 50g of Cauliflower in 200 mL of water for
30 seconds to get single cells.
- Strain through muslin cloth. Pour 15 mL of
liquid into a screw cap tube with 3 drops of detergent and shake gently
for 5 seconds.
- Carefully layer to top of tube with cold
alcohol (or meths). Use a hooked glass rod to spool out strands of DNA
at the interface.
To isolate your own human DNA
(an original protocol
independantly developed by Nexus, please acknowledge our contribution
if using this protocol for teaching purposes)
- To a 1/2 cup of water dissolve about 1/2
teaspoon of salt and add a squirt of dish-washing detergent. Save this
for step 3
- Swirl about 25 mls of water around your mouth
for 30 seconds. This removes some cheek cells. Spit into a disposable
- Add about 2cm of the fluid to a test-tube (or
a Fuji film cannister) and add about 1cm of the saline/detergent
solution. Invert gently 3 or 4 times to mix well (but you don't want a
lot of froth). This will break open the many cheek cells you spat out,
releasing the DNA message that each cell must carry.
- Layer on top some ice cold ethanol (or
methanol). Strands of DNA will be seen where the two layers meet. Hook
out the strands of DNA that form with a glass hook (or one made from a
plastic twist-tie) by slowly dipping up and down through the two layers.
CHEMICAL TESTS TO CONFIRM THE PRESENCE
The following chemical tests can be used to
check you actually have DNA:
- Test for purines: Add excess 2M ammonia
solution and a few drops of 0.1M silver nitrate to 1 mL of DNA extract.
A white precipitate indicates the presence of purines.
- Test for phosphate: Add 1 mL of 0.2M
ammonium molybdate (39.02g/L) to 0.5 mL of extracted DNA and warm
gently at 60-70oC. DO NOT BOIL. Yellow colour indicates presence of
- Test for deoxyribose: Add 2 mL of Disches
reagent to 1 mL of extracted DNA. Boil in water bath for 15 minutes.
Green-blue colour indicates presence of deoxyribose. Disches
reagent: 486 mL glacial acetic acid, 14 mL conc. sulphuric acid, 5g
diphenylamine. Stir well and add 500 mL distilled water
DeoxyriboNucleic Acid (DNA) is the
chemical message cells read to know what to do. Change the message and
you change the type of cell....change the cell and you change the
organ...change the organ and you change the whole organism. If the DNA
from a luminescent jellyfish is inserted into the DNA plan of a mouse
it could glow in the dark. This has actually been done! This creature
is now both jellyfish and mouse...a totally new lifeform through
DNA is made up of a series of only four
compounds; Adenine, Guanine, Thymine and Cytosine; an example is:
CAGATTCCAAACCGGGGGTTC; a unique piece of DNA "code" to tell the
cell what to do. The code is read in sets of three:-
CAG ATT CCA AAC CGG GGG TTC with each 3
letter combination telling the cell which one of the amino acids to use
in assembling PROTEINS the cell uses for work (enzymes), its structure
or shape, communication, movement, colour, etc. This simple set of four
bases read in groups of three allows for an almost infinite number of
different proteins to be made; an infinite number of different cells.
All bacteria, viruses, fungi, plants and animals use this same code. We
can swap DNA from one lifeform to another and it will be read!
ENGINEERS - VIRUSES: Viruses do not follow the MRSGREN
characteristics of living things. Scientists say that a living thing
must do 7 things: move, reproduce, sense the environment, grow in size,
respire, excrete wastes and use nutrients. Viruses do not sense the
environment, do not grow in size, do not carry out respiration, do not
make wastes, and do not consume food. A virus is simply a piece of DNA
(or RNA - Ribonucleic Acid) that is wrapped in a protein coat. This is
called the virus particle. Remember the points above about MRSGREN. We
say viruses are living in the loosest sense because they can reproduce:
A particle attaches itself to or enters a living cell. The DNA or RNA
is released into the cell The cell can’t tell the difference
between its original DNA instructions and the new ones. It follows the
new ones. New virus particles are assembled by the cell until it is so
full (about 100 to 1000) that it bursts and dies. Each new particle
will infect other cells.
Any drug that is used to stop viruses
reproducing must stop the host cell reproducing - even the healthy
ones! That is why there has never been a drug that can cure viral
diseases. Viruses have very short pieces of DNA or RNA (about 1000 to
9000 bases compared to billions in plants or animals). Any change to
the DNA or RNA (a mutation) caused by sunlight, chemicals, or copying
errors in cells have a significant impact on how the virus behaves. It
is estimated in a 24 hour period one strain of virus can mutate into
300 - 3000 different new strains. It may be possible that two different
viruses may infect the same host without causing symptoms and form a
hybrid eg, each year we see new strains of Flu virus that seem to be
part bird virus and part human virus.
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