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Lab DS1: Precipitating and Spooling DNA

"It took only a single event at the Whitehead to convert me. I saw DNA. From that moment on, I understood why molecular biologists are so enraptured by their subject . . . I thought that if I grabbed the DNA, I could roll it in my hands, twist it, pinch it, shape it into little animals, even drop it on the floor, and still it would jiggle merrily, holding life so firmly that it was on its own, alive. I might have thought I was being silly, reacting to purified DNA so strongly, if Ruth hadn't been equally captivated -- though she'd seen the substance many times before. We both stood there grinning like girls making fudge as she yanked out the DNA of the plant cells and prepared to do her experiments. I think that watching DNA come out of solution should be required of every high school student. Then perhaps people would realize that DNA is not a set of balls and sticks or a diminutive staircase."
      --Natalie Angier, Natural Obsessions,1988

You have read about deoxyribonucleic acid (DNA) . It is arguably the most important molecule in living things. It is a long, thin fiber that has the information necessary to control the chemistry of life. What does DNA look like? What are some of its many unique properties?

In this investigation, you will have the opportunity to precipitate and spool DNA onto a glass rod. The DNA has already been isolated from the nuclei of salmon sperm cells.

  • salmon sperm DNA in a buffered solution, 2 mL
  • strong NaCl solution [5M], less than 1 mL
  • ethyl alcohol, 4 mL
  • test tube
  • glass rod or Pasteur pipet
  • eye dropper

  1. Obtain 2mL of herring (or salmon) sperm DNA in a test tube. Examine it closely. Describe its appearance - color and viscosity.
  2. Add 4 or 5 drops of strong NaCl (sodium chloride) solution using an eye dropper, and MIX.
  3. Slowly trickle 4 mL of ethyl alcohol into the test tube containing the DNA and NaCl. DO NOT MIX.
  4. Observe the interface between the two solutions. You should see a layer of alcohol form on top of the layer containing the DNA and NaCl. Do not mix the two layers...yet.
  5. Place the glass rod or pipet all the way to the bottom of the test tube containing the two-layered solution.
  6. Watch the interface as you rotate the rod/pipet. Wind (spool) the DNA that comes out of solution on to the rod/pipet. These are not single DNA molecules, but thousands of molecules. If you have a partner, be sure to take turns spooling.
  7. Examine and touch the DNA on the rod. Record the appearance of DNA -- color and texture.
  8. When finished, ask your teacher what to do with your spooled DNA and glassware.

Activity Sheet

Name ______________________________________

Date __________ Period ____


1. Why is it important to study and understand DNA?


2. Describe in words and with a drawing the appearance of your isolated DNA:


3. Describe a follow-up activity that you could do using your isolated DNA:

Is It DNA?       Teacher Notes

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