Strawberry DNA Extraction Lab
Major Concept:
Cells are the basic unit of life and make up all plants, animals, and bacteria. Deoxyribonucleic acid, or DNA, is the
molecule that controls everything that happens in the cell. DNA contains instruction that directs the activities of
cells and, ultimately, the body. This activity will demonstrate how DNA can be isolated from a strawberry using
common household materials.
TEKS 14(C) recognize that inherited traits of individuals are governed in the genetic material found in the genes
within chromosomes in the nucleus.
Objectives:


To learn an easy way to extract DNA from a strawberry using household products
To see a large sample of DNA
Background:
This DNA extraction lab results in a large quantity of DNA that can be seen with the naked eye. It is an easy lab
activity, and if you follow the instructions, there is almost no way to make a mistake that would affect the results.
It is much more effective than extracting DNA from any other source because strawberries are soft and easy to
smash. In addition, ripe strawberries produce enzymes (pectinases and cellulases), which are chemicals that help
in breaking down the cell walls.
Strawberries have enormous genomes. Genomes are the genetic material of an organism. It is enclosed either in
DNA or, for many types of viruses, in RNA. The genome includes both the genes and the non-coding sequences of
the DNA/RNA. Humans have two copies of each chromosome (diploid genome). A chromosome is an organized
package of DNS found in the nucleus of the cell. Strawberries have up to eight copies of each chromosome
(octoploid genomes).
Materials:
DNA Extraction Material
1 sealable plastic bag
2 teaspoons of dish detergent
Strawberries – about the size of a golf ball
1 teaspoon salt
Glass cup
½ cup of water
Filtering apparatus: coffee filter
***Already prepared by your teacher
Ice cold 90% + Rubbing alcohol
Petri dish
Procedures:
1. Pull off any green leaves on the strawberry that have not been removed yet.
2. Put the strawberry into a plastic bag, seal it, and gently smash it for about two minutes. Completely crush
the strawberries. This starts to break open the cells and release the DNA.
Blending the strawberries, water, and salt together separated the strawberries into separate cells. But
each cell is surrounded by the cell membrane. DNA is found inside a second membrane (in the nucleus) within
each cell. To see the DNA, we have to break open these two membranes.
3. Add two teaspoons of the DNA extraction liquid into the bag with the strawberry. This will further break
up the cells.
We do this with detergent. Why detergent? How does detergent work? Think about why you use soap
to wash dishes or your hands – To remove grease and dirt – right?
Soap molecules and grease molecules are made of two parts: Heads, which “like” water and Tails,
which “hate” water. Both soap and grease molecules organize themselves in bubbles (spheres) with heads
outside to face the water and tails inside to hide from the water.
When soap comes close to grease, it captures it, forming a greasy soapy ball.
A cell’s membranes have two layers of lipid (fat) molecules with proteins going through them. Fats act like grease
detergent.
When detergent comes close to the cell, it captures the lipids (fats) and proteins.
4. Reseal the bag and gently smash for another minute. Avoid making too many soap bubbles.
5. Place the coffee filter inside a plastic cup.
6. Open the bag and pour the strawberry liquid into the filter. You can twist the filter just above the liquid
and gently squeeze the remaining liquid into the cup.
Enzymes are proteins that help chemical reactions happen more quickly. Without enzymes, our bodies
would come to a halt. In this investigation, the enzymes at work are naturally found in the strawberries. The
enzymes are pectinase and cellulase and it’s their job is to cut proteins.
After you added detergent, the cell and nuclear membranes had been broken apart. The DNA in the nucleus
of the cell is molded, folded, and protected by proteins. The enzymes, pectinase and cellulase, cut the proteins
away from the DNA.
7. Next. Pour down the side of the cup an equal amount of cold rubbing alcohol as there is strawberry liquid.
DO NOT MIX OR STIR. You have just isolated the DNA from the rest of the material contained in the cells
of the strawberry.
8. Within a few seconds, watch for the development of a white cloud substance (DNA) in the top layer above
the strawberry extract layer.
Alcohol is not as dense as water, so it floats on top. Look for clumps of white stringy stuff where the
water and alcohol layers meet.
DNA is a long, stringy molecule. The salt that you added in Extraction Material helps it stick together. So
what you see are clumps of tangled DNA molecules!!!
DNA normally stays dissolved in water, but when salty DNA comes in contact with alcohol, it becomes
un-dissolved. This is called precipitation. The physical force of the DNA clumping together as it precipitates pulls
more strands along with it as it rises into the alcohol. You are done and have successfully EXTRACTED DNA!!!
9.
10.
11.
12.
Tilt the cup and pick up the DNA using a toothpick and place it in a petri dish.
Pull apart an extremely small piece of the DNA and place it on a concave microscope slide.
Using a pipette, add a little bit of solution on the slide and place a slip cover on top of the DNA.
Observe the DNA using a hand lens and with a compound microscope. Begin with the lowest objective
first.
13. If you do not remember the proper microscope procedures be sure to ASK for help before you begin!
Deoxyribonucleic acid (DNA) is the genetic material present in all living organisms, from bacteria to humans. A
single subunit of DNA is called a nucleotide and is made of a nitrogen-containing base, a sugar, and a phosphate
group. Hundreds of thousands of nucleotides are hooked together to form a chain. Two chains are paired
together and twisted into a double helix to form the finished DNA molecule:
In organisms such as humans, DNA is paired with protein in structures called chromosomes that are inside the
cell’s nucleus.
DNA is material that controls the genetic traits of all living things. DNA is a long, but narrow string-like
object. A one foot long string of DNA is normally packed into a space about the size of a cube 1/1,000,000 of an
inch on a side. This is possible only because DNA is a very thin string.
Our body’s cells each contain a complete sample of our DNA. One cell is roughly equal in size to the cube
described in the previous paragraph. There are muscle cells, brain cells, liver cells, sperm cells and others.
Basically, every part of the body is made up of these tiny cells and each contains a sample or complement of DNA
identical to that of every other cell within a given person. There are a few exceptions. For example, our red blood
cells do not have DNA because they don’t have a nucleus. Blood itself can be typed and identified because of the
DNA contained in other cells in the blood, like white blood cells.
A strand of DNA is made up of tiny building blocks. There are only four different basic building blocks. The
letters are: A, T, G, and C. These four letters are short nicknames for more complicated chemical names: Adenine,
Thymine, Guanine, and Cytosine. Another way of referring to the building blocks or letters is to call them bases.
For example, to refer to a particular piece of DNA, we might write: AATTGCCTTTTAAAAA. This is a
perfectly acceptable way of describing a piece of DNA.
The order or sequence of the bases (letters) can code for many properties of the body’s cells. The cells can
read this code. Some DNA sequences code important information for the cell. Such DNA is called, not surprisingly,
“coding DNA.” Our cells also contain much DNA that doesn’t code anything that we know about. If the DNA
doesn’t encode anything, it is called non-coding DNA or sometimes, “junk DNA.”
The DNA code, or genetic code as it is called, is passed through the sperm and egg to the offspring. A
single sperm cell contains about three billion bases consisting of A, T, G, and C that follow each other in a welldefined sequence along the strand of DNA.
Both coding and non-coding DNA may vary from one individual to another. These DNA variations can be
used to identify people, or at least tell one person from another.
This lab has been modified from “DNA – The Stuff of Life” and “How to Extract DNA from Almost
Anything Living.” (University of Utah) and “How to Extract DNA from a Strawberry” from National
Human Genome Research Institute.
Lab Questions:
1. Does the DNA have any color?
2. Describe the appearance of the DNA.
3. Do only living things contain DNA? Justify your answer.