DNA Extraction: DNA Structure and Function
Lesson 16 of 19
Objective: SWBAT explore DNA structure and function through a DNA extraction.
This lesson builds the foundational knowledge that students will need to know in order to address the following inheritance and variation standards:
MS-LS3-1. Develop and use a model to describe why structural changes to genes (mutations) located on chromosomes may affect proteins and may result in harmful, beneficial, or neutral effects to the structure and function of the organism.
MS-LS3-2. Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation.
Knowledge of the structure and as a result the function of DNA (CCC-Structure and Function) is needed to understand both effects of genetic mutations, asexual, and sexual reproduction.
In this section of the lesson I engage students by visiting Zooming into DNA.
This site allows students to see the size and scale of DNA when compared to other objects such as tissue, cells, viruses, and chromosomes.
Students are required to write down the name of each object and its magnification along with two facts.
In this explore section of the lesson students complete a DNA Extraction courtesy of Genetic Science Learning Center. (SP3 - Planning and Carrying out Investigations)
DNA Source (for this experiment we use green peas), other sources are below.
• Chicken liver
Step 1 Blender Insanity!
Put in a blender:
• 1/2 cup of peas (100ml)
• 1/8 teaspoon table salt (less than 1ml)
• 1 cup cold water (200ml)
Blend on high for 15 seconds.
The blender separates the pea cells from each other, so you now have a really thin pea-cell soup.
Step 2 Soapy Peas
Pour your thin pea-cell soup through a strainer into another container (like a measuring cup).
Add 2 tablespoons liquid detergent (about 30ml) and swirl to mix.
Let the mixture sit for 5-10 minutes.
Pour the mixture into test tubes or other small glass containers, each about 1/3 full.
Step 3 Enzyme Power
Add a pinch of enzymes to each test tube and stir gently. Be careful! If you stir too hard, you’ll break up the DNA, making it harder to see.
Use meat tenderizer for enzymes. If you can’t find tenderizer, try using pineapple juice or contact lens cleaning solution.
Step 4 Alcohol Seperation
Tilt your test tube and slowly pour rubbing alcohol (70-95% isopropyl or ethyl alcohol) into the tube down the side so that it forms a layer on top of the pea mixture. Pour until you have about the same amount of alcohol in the tube as pea mixture.
Alcohol is less dense than water, so it floats on top. Look for clumps of white stringy stuff where the water and alcohol layers meet.
Step 5 DNA Time !!!
DNA is a long, stringy molecule. The salt that you added in step one 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 undissolved. 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 can use a wooden stick or a straw to collect the DNA. If you want to save your DNA, you can transfer it to a small container filled with alcohol.
In terms of how I completed this activity I had groups of 4 students come to station where all material where accessible. All groups followed lab procedure in DNA Extraction protocol.
I have included video below of two students completing above procedure.
Teacher Note: I have attached a link to Do-it-Yourself Strawberry DNA which has a step by step guide on how to complete a Strawberry DNA extraction including video tutorials.
In this section of lesson I explain the DNA process by completing a virtual DNA extraction from Learn.Genetics.
Description of Virtual Lab
DNA is extracted from human cells for a variety of reasons. With a pure sample of DNA you can test a newborn for a genetic disease, analyze forensic evidence, or study a gene involved in cancer. Try this virtual laboratory to perform a cheek swab and extract DNA from human cells.
As I complete virtual extraction on the SmartBoard, I have students focus on the following questions:
1. What are some reasons that people need to isolate/extract DNA?
2. Where do scientists need first to begin DNA extraction?
3. Where is the source of cells in this lab?
4. What are the steps needed to purify DNA from a cheek swab?
To evaluate lesson I have students complete a Four-Square Synectics on DNA structure and function.
Synectics provides a metacognitive opportunity for students to examine abstractly what they know about a concept. This strategy uses analogies or metaphors to connect students' ideas with a concept. Information gathered from assessment can be used by teacher to plan additional opportunities to develop conceptual understanding.
Design and Administration
Students are provided with a chart containing four boxes below. Students are required to complete fill sentence frame below using the word from each box. (Example: DNA is like a cell phone, because it allows for a large amount of information to be communicated.)
After students have filled in their Synectics chart, have pairs of students share their analogies or metaphors with each other and then with the class.
DNA is like a(n) _________________________ because _____________________.
Teacher Note: I have included DNA Is Like Synectics Chart