Deoxyribonucleic Acid, or DNA, is a self-replicating molecule that instructs an organism or form of life on how to develop, live, and reproduce. DNA holds the genetic information necessary to all forms of life. When talking about DNA, it is important to specify that all organisms hold DNA. An organism does not have to have a beating heart or any type of organ at all. In fact, fruits, vegetables, and even nuts have DNA. DNA extraction is the act of seperating DNA from an organism, for example, the act of extracting DNA from a banana. Depending on the school district, students can learn about DNA and chromosomes between late middle school and high school. Many students learn efficiently when they are able to participate in an activity or learn visually. Now, I don't mean a powerpoint presentation is the best option for learning about complex molecules and chromosomes, scientific experiments and demostrations will most likely interest students. I extracted DNA from a strawberry as an experiment and introdution to DNA and genetic biology. This is a great way to introduce your students to the complex world of genetic biology. You will be able to introduce your students to mitochondrial DNA, lipids, A.G.C.T., genes, and more. I will explain in context what each one is, in which order to teach, and define vocabulary words. This experiment is educational, fun, inexpensive and will only take about 10-15 minutes.
- Isopropanol (Isopropyl Alchohol)
- 4 Strawberries (per every pair/group)
- Dish Soap
- Paper Towel or Coffee filter
- Popsicle Stick
- Freezer or Cooler with ice inside
- Warm or Boiling water
- Glass cup
- Tall glass or clear measuring cup
- Optional: Microscope
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Step 1: Prepare and Plan Ahead
Make sure to gather all of your materials at least 3 days prior to the experiment as some materials require preparation beforehand. This experiment also may get messy, so make sure that you provide proper sanitation to the work area (meaning make sure that you have gloves because the strawberry may stain your hands as well as light tabletops. I suggest placing a mat under the materials or even a plastic tablecloth or paper towels). About 15-30 minutes prior to the experiment, the isopropyl alchohol will need freezing, so be sure to have access to a freezer or cooler. Also, you will need warm-hot water or boiling water. You can use the hot water from coffee machines, and if you prefer stovetop boiling, there will be instructions for when the water should be used and more. I did this experiment at my house and found that it was very easy in terms of materials. I did not need to go anywhere, which may be beneficial to effort put into the materials. As long as about 30 minutes or less prior to the experiment you are available, you will be good for preparation.
Step 2: Prepare the Saltwater
Around 10 minutes before the experiment, boil 1 cup of water at medium-high heat for 5 minutes or until it comes to a boil. You can also use warm water from a coffee machine around 5 minutes prior if you do not have access to a stovetop. Once boiled, set aside for one minute and pour into a clear, glass cup. Add 1 teaspoon of salt and mix until dissolved, or until there aren't any visible salt crystals.
Step 3: Mash the Strawberries
To prepare the strawberries, slice 4 large strawberries into fourths and place them into a heavy duty Ziploc freezer bag. Mash them with your hands until it is mostly strawberry juice and there are few strawberry chunks. Once it is at a good consistency, proceed to the next step.
Step 4: Make Strawberry Formula
To create the strawberry formula, add most if not all of the saltwater solution as well as 4 tablespoons of dish soap to the strawberry liquid. Mix until combined, and use a paper towel or coffee filter to filter the chunks of strawberry. I cut a hole on the corner of my Ziploc bag to keep a steady flow and squeezed the filter to get the most strawberry liquid as possible. I resulted in a little less than 4 oz. of liquid.
Step 5: DNA Extraction
Once the strawberry formula is complete, remove the isopropyl alcohol from the freezer/cooler and tilt the strawberry formula glass 90 degrees and pour around 5-6 tablespoons of rubbing alcohol, or until a clear layer of about 1 inch is visible. Small bubbles will begin to form, and a "snot"-like substance will form. This substance is your strawberry DNA! You can place it under a microscope, store it in an airtight container, or do as you wish with the specimen.
Step 6: Teaching Strategy
The following examples of teaching explain concepts of genetic biology, forensics, and more. I will explain 5 concepts in a specific order designed to introduce these complex concepts when based off of the original idea of DNA extraction. I will also explain and define vocabulary words, important concepts, and provide examples and images:
-DNA- Short for deoxyribonucleic acid, DNA is a self-replicating material found in almost all organisms that contains genetic information and is what is called "a map" or "a key" of an individual organism. In a human for example, this individual's eye color, hair color, nose shape, skin tone, and every characteristic of this human's body depends on its DNA. The information in DNA comes from a code of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The sequence of these bases determines the information for this organism to live and maintain, similarly configured as letters in the alphabet would be arranged to create words. . Each base is attached to a sugar and phosphate molecule. DNA's double-helix shape is composed of base pairs: Adenine and Thymine, Guanine and Cytosine. It is also composed of a "sugar-phosphate backbone," creating a recognizable double helix pattern.
-Cells- Cells are the basic building blocks of all organisms. (According to Genetics Home Reference) Human cells are composed of these basic parts:
- Cytoskeleton- The cytoskeleton is a network of long fibers that make up the cell’s structural framework. The cytoskeleton has several critical functions, including determining cell shape, participating in cell division, and allowing cells to move. It also provides a track-like system that directs the movement of organelles and other substances within cells.
- Cytoplasm- Within cells, the cytoplasm is made up of a jelly-like fluid (called the cytosol) and other structures that surround the nucleus.
- Endoplasmic reticulum- This organelle helps process molecules created by the cell. The endoplasmic reticulum also transports these molecules to their specific destinations either inside or outside the cell.
- Golgi apparatus- The Golgi apparatus packages molecules processed by the endoplasmic reticulum to be transported out of the cell.
- Lysosomes and peroxisomes- These organelles are the recycling center of the cell. They digest foreign bacteria that invade the cell, rid the cell of toxic substances, and recycle worn-out cell components.
- Mitochondria- Mitochondria are complex organelles that convert energy from food into a form that the cell can use. They have their own genetic material, separate from the DNA in the nucleus, and can make copies of themselves.
- Nucleus- The nucleus serves as the cell’s command center, sending directions to the cell to grow, mature, divide, or die. It also houses DNA (deoxyribonucleic acid), the cell’s hereditary material. The nucleus is surrounded by a membrane called the nuclear envelope, which protects the DNA and separates the nucleus from the rest of the cell.
- Plasma membrane- The plasma membrane is the outer lining of the cell. It separates the cell from its environment and allows materials to enter and leave the cell.
- Ribosomes- Ribosomes are organelles that process the cell’s genetic instructions to create proteins. These organelles can float freely in the cytoplasm or be connected to the endoplasmic reticulum.
-Chromosomes- Chromosomes are thread-like structures in which DNA is held in the nucleus of a cell. Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the chromosome is labeled the “q arm.” The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.
-Genes- Genes are composed of DNA. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases. Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s unique physical features. When relating to things like family trees, genes from physical features, behavior, and diseases can be passed down in the family tree.
-Forensic Biology- Biology can be incorporated with forensics as forensic scientists gather important pieces of evidence like saliva, blood, hair, and more. Scientists can analyze the sample as a specimen and gather DNA from the sample. They can then infer who may be a suspect or analyze who may have been associated with a crime.
These 5 important vocabulary words are necessary to understand this unit and are main concepts of the lesson. All definitions are from the Merriam-Webster Dictionary.
Definition: any of various nucleic acids that are usually the molecular basis of heredity, are constructed of a double helix held together by hydrogen bonds between purine and pyrimidine bases (see BASE entry 1 sense 6b) which project inward from two chains containing alternate links of deoxyribose and phosphate, and that in eukaryotes are localized chiefly in cell nuclei.
Definition: a specific sequence of nucleotides in DNA or RNA that is located usually on achromosome and that is the functional unit of inheritance controlling the transmission and expression of one or more traits by specifying the structure of a particular polypeptide and especially a protein or controlling the function of other genetic material.
Definition: any of the rod-shaped or threadlike DNA-containing structures of cellular organisms that are located in the nucleus of eukaryotes, are usually ring-shaped in prokaryotes (such as bacteria), and contain all or most of the genes of the organism. Also : the genetic material of a virus.
Definition: a small usually microscopic mass of protoplasm bounded externally by a semipermeable membrane, usually including one or more nuclei and various other organelles with their products, capable alone or interacting with other cells of performing all the fundamental functions of life, and forming the smallest structural unit of living matter capable of functioning independently.
Definition: a branch of knowledge that deals with living organisms and vital processes.
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Thank you for reading and I hope you enjoy this experiment at home or in the classroom!
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