Download The Molecule of Life: DNA

The Molecule of Life:
DNA
The Molecule of Life: DNA
• The purpose of this laboratory exercise is to
extract and visualize DNA from fruit.
• The objectives of the laboratory exercise are:
To understand where DNA is found
To isolate DNA
To understand how DNA is extracted
To learn about positive and negative controls
The “rungs” are made up of four
Our body is made up of about
bases: A, G, T, C.
100 trillion cells.
That’s 100,000,000,000,000!
Each cell contains the entire
human
genome.
When
unfolded,
DNA looks like a
double helix: a twisted ladder
Cells differentiate by turning on and
off different genes.
DNA is looped and folded so long
stretches can be fit into a nucleus
Inside the cell, DNA is found in the
nucleus
The DNA is organized
into have many
Chromosomes
chromosomes: thegenes:
humanthese
genome
are small
has 46 chromosomes
sections of DNA that code for
Adapted from “Journey into DNA”
http://www.pbs.org/wgbh/nova/geno
me/dna.html
a particular protein
What does DNA look like?
• DNA contains one of four
nucleotides: adenine (A),
thymine (T), cytosine
(C), and guanine (G).
• A+T or C+G
The role of
the
nucleotides
• The different nucleotides spell out a code: instructions for the
cell
• Each set of instructions is a gene. A gene is a long series of the
four letters (nucleotides) that gives instruction to the cell.
Lab Protocol
• Step 1 – Prepare Materials & Solutions
Solutions
DNA Buffer: Combine 120 mL of dH2O (distilled water) with 1.5 g salt
(noniodized), 5 g baking soda and 5 mL dishwashing liquid.
• Materials
Ziploc bag
Pipet Bulb
(3) 10mL Pipettes
Distilled Water Fruit Sample Box of Kimwipes
Buffer
Cheesecloth
Ethanol (95 – 100 percent)
Test Tube Rack
15 mL conical tubes
Glass rod or wooden stick
Metal Spatula
Black paper
50 mL conical tube
Gloves
Scissors
• Step 2 – Prepare tubes
Label the 15 mL conical tubes with your initials or group
name.
Put on your gloves!
• Step 3 – Prepare Experimental Samples
Weigh out 7.5 g of the fruit from which you will be isolating
DNA
In the ziploc bag, combine the fruit with
7 mL of dH2O
3 mL of buffer solution
Grind the mixture into a fine paste.
Why do we crush the fruit?
So we can break apart and open the cells.
Why do we add buffer solution?
- Detergent breaks open membranes to release DNA
- Baking soda neutralizes so DNA is not degraded
Filter the mixture through at least two layers of
cheesecloth into a 50 ml plastic tube.
Transfer 2 mL of the filtered mixture to the
15ml tube labeled with your initials or group
names
• Step 4 – DNA Isolation
Add 1 mL of DNA Buffer to the 15 ml tube. Cap and gently
invert to mix.
Add 2 mL of ice-cold ethanol slowly down the side of each
tube to form a layer that floats on top of each sample.
Why add ethanol?
Ethanol is less dense than water so it floats
on top. All of the proteins we broke up in
Step 4 will sink to the bottom; the DNA will
float on top.
• If there is DNA
present in any of the
samples it should
precipitate out in gray
clumps that may look
like white fine lint
fibers.
• Use a glass rod to
spool out the DNA
clumps and place
them on black paper
for observation.
What can we do with DNA?
What kinds of jobs involve working
with DNA?
Other ways of visualizing DNA
DNA can be run on an agarose gel, which separates DNA pieces based
on size. A charge is applied, and because DNA is slightly negatively
charged, it will run through the gel towards the positive charge.
Larger
pieces of
DNA
Smaller pieces
of DNA can
more easily
move through
the gel and will
end up closer
to the bottom.
Smaller
pieces of
DNA
+
Other ways of visualizing DNA
DNA can also be sequenced. These techniques allow
us to determine the order of nucleotides (the code).
Being able to “read
the code” allows
us to identify
genes and
compare
organisms.
Careers in Molecular Biology
Because we inherit genes from
our parents, we can use DNA
sequences to determine how
organisms are related.
Ecologists and conservation biologists
use DNA to understand population
structure: this can help identify and protect
endangered species
Animal breeders use
differences in DNA to
determine parentage.
Careers in Molecular Biology
Genetic engineers can change gene sequences, or
insert new genes to improve organisms.
Microorganisms can be
genetically engineered to
produce pharmaceuticals. For
example, the human insulin gene
is inserted into bacteria to mass
produce insulin for diabetics.
Genes are inserted into
crops to make them
mold and pest resistant
Careers in Molecular Biology
Medical professionals and gene therapists use DNA sequences to
understand the variation between people in terms of health and
disease. This is important in the study of heritable disease (such as
breast cancer), organ transplants, and fertility.
Pharmaceutical scientists also use DNA techniques to understand how
drugs work in the body, which helps them develop new and better drugs.
Careers in Molecular Biology
There are slight differences in the
DNA sequences between different
people.
Forensic scientists and
crime scene investigators
use these differences to help
match DNA found at a crime
scene to a suspect.
Found at the
crime scene
Suspects:
A
B
WHO DID IT?
C