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Extracting DNA  

Student Activity


Introduction
In the Space Station Alpha mission preparation, your students learned that the solar storm represents a great danger to the astronauts if they are not shielded from the damaging radiation of the sun. The solar rays can penetrate the layers of the space station and damage the astronauts’ DNA, the genetic material that produces our characteristics, or traits.

The damage that may occur to the DNA contained in the cells may result in mutations that get passed along when the cell divides to form a new cell. A mutation is a random change in a gene or chromosome that results in a new trait. Mutations can alter the way the cell works and may have dangerous consequences, such as cancer, to the astronauts. For this reason the radiation levels of every astronaut are carefully monitored.

Every living thing contains DNA. The same type of DNA that is responsible for your traits also produces and controls the traits of other living things, although the amount and the coding are different.

Today, scientists analyze the DNA from minute samples of blood, hair, saliva, and other body fluids. They use the analyses for many different scientific studies. Forensic studies use DNA to solve crimes and identify victims. Anthropological studies use DNA to help identify how different animals may have been related. Scientists can even determine why the famous chemist, John Dalton, was colorblind by analyzing his preserved eyeballs.

But before scientists can analyze the DNA, they must be able to extract (remove) it from the cell that surrounds it.

This lesson reviews DNA, genes, chromosomes, and mutations to reinforce the concepts of the Space Station Alpha mission and to allow you to more fully realize the importance of the shielding procedures during your mission. After reviewing the basic information, you will do an experiment in which you will separate out DNA from peas. Knowing that DNA can be separated will give you a better understanding of the concept of the solar storm radiation affecting DNA and also a base of understanding for future lessons in biology, evolution, biotechnology, and health technology.

Skills
You practice measurement and laboratory skills and techniques through the extraction of DNA from pea cells. You must read and follow procedure to extract the DNA. Critical thinking skills are enhanced through troubleshooting any problems that occur.

Objectives
You will:
  • Develop an understanding of DNA by modeling the process of DNA extraction.

  • Practice laboratory techniques to carry out an investigation.

  • Use critical thinking skills by understanding the concept of DNA in cells and the extraction procedure.

  • Relate the procedure and the topic to your mission.
Activity Overview
This laboratory exercise is designed to give you an opportunity to extract DNA from peas. DNA is removed from the peas by blending, treating it with soap, and mixing it with an enzyme. DNA is precipitated out of solution by using an alcohol (ethanol).

Key Questions
  • Why is DNA so important?

  • Where is DNA found?

  • What are the consequences to damaging radiation in space?
Key Concepts
  • Damaging solar radiation can penetrate the layers of the space station and cause damage to the astronauts’ DNA.

  • DNA is the genetic material that produces our characteristics, or traits, and is contained in nearly every cell of our bodies.

  • Any damage that may occur to the DNA may result in mutations that get passed along when the cell divides to form a new cell.

  • During the Space Station Alpha mission you must investigate and implement shielding procedures to protect the astronauts against damaging solar radiation.
Materials
  • Blender
  • Strainer
  • Graduated cylinder or tablespoon
  • Test tubes or other small glass containers
  • Rubbing alcohol
  • Split peas
  • Water
  • Liquid detergent
  • Meat tenderizer
Vocabulary
  • chromosome: structure in the cell nucleus that carries the genes that determine the characteristics an organism inherits from its parents.

  • DNA: the major component of chromosomes that carries the genetic information; has a twisted double-stranded form.

  • enzyme: a protein produced by living cells that promotes a chemical reaction.

  • gene: a basic unit of transmitting characteristics from one generation to the next. It consists of a specific sequence of DNA that occupies a certain and fixed position on a chromosome.

  • mutation: a random change in a gene or chromosome that results in a new characteristic.

  • radiation: energy emitted in rays or waves; some radiation, such as X-rays, is harmful.

  • traits: a characteristic, such as eye color, hair color, or correct cell function.

Procedure
  1. 1. Add together in a blender:
    • 1/2 cup of split peas (100ml)
    • 1/8 teaspoon table salt (less than 1ml)
    • 1 cup cold water (200ml)

  2. Blend on high for 15 seconds. (The blender separates the pea cells from each other.)

  3. Pour the thin pea-cell soup through a strainer into another container, such as a beaker.

  4. Add two tablespoons liquid detergent (about 30ml) and swirl to mix. (A cell’s membrane has two layers of lipid (fat) molecules. The detergent breaks apart the fats and the proteins to dissolve the cell membranes and allows the DNA to “come out” into the solution.)

  5. Let the mixture sit for 5-10 minutes.

  6. Pour the mixture into test tubes or other small glass containers, each about ? full.

  7. Add a pinch of the meat tenderizer (an enzyme) 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.

    (If you can't find tenderizer, try using pineapple juice or contact lens cleaning solution.)

    An enzyme is a chemical that promotes a reaction. In this case it breaks up the proteins that surround the DNA.

  8. Tilt your test tube and slowly pour rubbing alcohol (70-95 percent 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 the pea mixture.

    The alcohol floats on top of the water/pea mixture and allows better isolation of the DNA which also comes to the top.

  9. DNA will rise into the alcohol layer from the pea layer. Use a wooden stick or glass rod to gently draw the DNA into the alcohol.

  10. Alcohol is less dense than water, so it floats on top. The DNA will stay in the top alcohol layer while the protein parts of the cell sink to the bottom. The DNA will appear as a long, stringy clump.
You have now isolated and separated the DNA material from this organism (a pea plant)! Can you think of ways to measure how much DNA you got from the sample? How would the procedure have to change to allow for an accurate measurement?

Reflection and Discussion
  1. What is DNA?






  2. What are some things DNA determines?






  3. Where is DNA?






  4. What are chromosomes made of?






  5. Why do astronauts have to worry about radiation in space causing changes or mutations in the DNA in their cells?






  6. Describe the DNA you extracted from the pea plant.






  7. Do you think the DNA would look different or similar if you used another source for the DNA extraction procedure? Explain your answer.


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