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DNA: What Does It Mean?
by Nate Hespelt and Adriane Cej
University of Idaho




Illustrate the concept of the structure of DNA. Following a brief lecture over the composition and structure of DNA, students will explore and manipulate the three dimensional structure of DNA using an online DNA tutorial. Students will then view a video segment which describes the process of DNA extraction and its applications. Following the video presentation, students will perform their own DNA extraction from a clove of garlic. Students will identify the key components of DNA, the phosphate backbone, the five-carbon sugar, and the nucleotide pairs and the number of hydrogen bonds between them. Major concepts: DNA, double-helix, major groove, minor groove, phosphate backbone, five-carbon sugar, nucleotide, purine, pyrimidine, adenine, guanine, cytosine, thymine, hydrogen bond.


  • Students will describe the composition and structure of a DNA molecule. (Comprehension)
  • Students will summarize the process of DNA extraction. (Knowledge of a process)
  • Students will describe, in their own words, one application of DNA extraction in scientific research. (Comprehension)
  • Given a clove of garlic, students will extract a sample of DNA. (Application).
  • Students will list the three steps necessary in extracting DNA from the cells in a garlic clove.
    a) Lyse cell walls and membranes
    b) Breakdown the protein/DNA structure
    c) Precipitate DNA
  • Students will explain the role of buffer solution and each ingredient of the buffer.
  • Buffer - solution used to maintain a pH within certain limits
    1 - salt - interferes with protein/DNA structure
    2 - baking soda - interferes with protein/DNA structure
    3 - shampoo - lyses cell walls and membranes
    4 - water - used to dissolve ingredients into solution
  • Students will explain the role of isopropyl alcohol in the extraction of DNA from garlic cells. DNA precipitates (decrease in salt concentration) and becomes "visible" most proteins and other cellular junk remain in buffer solution.
  • The students will describe, in their own words, the structure of DNA.
  • Students will "see" the structure of DNA.


  • What are the three steps in extracting DNA from a clove of garlic?
  • What is the purpose of using a buffer?
  • What is the purpose of using salt, baking soda, shampoo and water to make the buffer?
  • What is used to extract/precipitate the DNA from the garlic extract?


  • KWL forms
  • DNA lecture notes and/or Powerpoint presentation
  • PC computers with internet access.
  • Tutorial program: "DNA - An introductory level nonlinear self-paced tutorial."
  • Worksheet for each student.
  • Video Tape segment: "Real Science - High Tech" (Segment beginning 17 min. into broadcast to 28 min.)
  • Safety Goggles
  • Text: Biology: Principles & Exploration (Johnson and Raven).
  • Boxlight® Projector Chime Resources, by Eric Martz, University of Massachusetts, Amherst
    chime/dna/ fs_pairs.htm

  • CHIME plug-in
  • Worksheet to accompany tutorial: DNA - An Intro level nonlinear self-paced tutorial
  • Solutions: Buffer (10 extractions)
    120 mL water
    1.5 g (1/4 tsp.) pure table salt - not iodized
    5 g (1 tsp.) baking soda - sodium bicarbonate 5 mL (1 tsp.) shampoo or liquid laundry detergent
  • Garlic Mash (1 extraction)
    1 clove of garlic
    10 mL water
  • Extraction (1 extraction)
    10 mL isopropyl alcohol
  • Glassware: (1 extraction)
    1 - 100 mL graduated cylinder/measuring spoons
    1 - 50 mL graduated cylinder/measuring spoons
    1 - 120 mL Erlenmeyer flask/clear glass drinking cup
    2 - 100 mL beakers/clear glass drinking cup
    1 - test tube/clear shot glass
  • Miscellaneous equipment:
    garlic press
    disposable glass pipette/drinking straw
    filter paper/coffee filte
    glass stirring rod/spoon
    glass stirring rod/plastic or wood stirring straw
    scale/measuring spoons
    ice/water bath



Students will be given a KWL form divided into three vertical columns. Prior to the lesson, students will fill in the "K" column by answering the following question: "What do you know about DNA?"

Students will then complete the "W" column by answering the following question: "What do you want to know about DNA? (Come up with as many questions as you can.)"

Following the lesson, students will fill in the "L" column by answering the following question: "What have you learned about DNA and its technological applications?"

Teacher will provide a brief lecture describing the basic structure and composition of DNA using visual aids such as a Powerpoint or overhead presentation.



The lecture will include the following components:

  • DNA is a long molecule made up of subunits called nucleotides.

  • Each nucleotide is made up of three parts: a phosphate group, a five carbon sugar called deoxyribose, and a nitrogenous base.

  • While the phosphate group and the sugar molecule are the same for each nucleotide in a molecule of DNA, the nitrogenous base may be any one of four different kinds.

  • The four types of nitrogenous base include the following: adenine, guanine thymine, and cytosine.

  • Adenine and guanine are purines, with a double ring of carbon and nitrogen atoms.

  • Thymine and cytosine are pyrimidines, with a single ring of carbon and nitrogen atoms.

  • The DNA molecule forms a double helix configuration, as adenine will only form hydrogen bonds with thymine and cytosine will only bond to guanine.

  • These base pairing rules determine the precise arrangement of nucleotides within a DNA molecules.


Students will explore and manipulate the three dimensional structure of DNA using an online DNA tutorial. At their computers (in groups if necessary), have students access the following web site:


Note: Chime Plug-in required. Have students familiarize themselves with the functions of the tutorial. As the students explore the tutorial, have them complete the accompanying worksheet: DNA - An Introductory level non linear self-posed tutorial.


To give students a specific responsibility for viewing have students write down the method the scientist uses to extract DNA and for what purpose.


START video approximately 17 minutes into broadcast where Grace Cacalano, a molecular biologist for the Genentech Corporation comes on screen. Play until end of tape (about 10 minutes) Discuss what advances in biological knowledge have spurred the field of biotechnology. Discuss what is Biotechnology and why it is important.


DNA Extraction Activity

Students will perform their own DNA extraction from a clove of garlic. Safety considerations: All equipment and solutions are to be used in a responsible manner. Protective eyewear is required.


  • Place bottle of isopropyl alcohol in freezer.

  • Combine ingredients (see materials list) for buffer solution in a 120 ml flask, swirl until mixed and place in ice water bath.

  • Using garlic press, press one clove of garlic into clean 100 ml beaker.

  • Pour 10 ml water into beaker with pressed garlic and mix with stirring rod.

  • Combine 5 ml garlic extract and 10 ml chilled buffer solution. Stir vigorously for 3 min.

  • Fold filter paper so it will rest on opening of unused beaker/shotglass.

  • Pour garlic mash into filter and let garlic extract drip through filter.

  • While tilting test tube slightly, pour 10 ml alcohol down side of the test tube using glass pipette/drinking straw. The alcohol should form a distinct layer on top of the garlic extract. Be careful not to mix the two!

  • Slowly insert the stirring rod through the alcohol layer to the garlic extract.

  • Gingerly use the stirring rod to swirl the liquids at the interface between the garlic extract and the isopropyl alcohol. The DNA should precipitate and stick to stirring rod.

  • Have students answer questions on worksheet: Demonstration DNA Extraction.

  • For additional lesson plans and ideas relating to this topic and many others try TeacherSource at PBS Online! You will find activities, lesson plans, teacher guides and links to other great educational web sites! Search the database by keyword, grade level or subject area! Mathline and Scienceline are also great resources for teachers seeking teaching tips, lesson plans, assessment methods, professional development, and much more!

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