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 understand where DNA is found
To isolate DNA
To understand how DNA is extracted
To learn about positive and negative controls
Our body is made up of about 100 trillion cells.
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 chromosomes: the human genome has 46 chromosomes
Chromosomes have many genes: these are small sections of DNA that code for a particular protein
Adapted from “Journey into DNA” http://www.pbs.org/wgbh/nova/genome/dna.html
DNA Buffer: Combine 120 mL of dH2O (distilled water) with 1.5 g salt (noniodized), 5 g baking soda and 5 mL dishwashing liquid.
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
Label the 15 mL conical tubes with your initials or group name.
Put on your gloves!
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.
So we can break apart and open the cells.
Why do we add buffer solution?
- Detergent breaks open membranes to release DNA
Transfer 2 mL of the filtered mixture to the 15ml tube labeled with your initials or group names
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.
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.
+Other ways of visualizing DNA
Smaller pieces of DNA can more easily move through the gel and will end up closer to the bottom.
Larger pieces of DNA
Smaller pieces of 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.
Animal breeders use differences in DNA to determine parentage.
Ecologists and conservation biologists use DNA to understand population structure: this can help identify and protect endangered species
Microorganisms can be genetically engineered to produce pharmaceuticals. For example, the human insulin gene is inserted into bacteria to mass produce insulin for diabetics.
Genetic engineers can change gene sequences, or insert new genes to improve organisms.
Genes are inserted into crops to make them mold and pest resistant
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.
A B C
Found at the crime scene
WHO DID IT?
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.