Isolation of Dna from an Onion

Isolation of Dna from an Onion

Extracting DNA from Your Cheek

INTRODUCTION: For many years DNA has been an elusive material to view in its natural form. All living things contain DNA in its cells or cell. Some organisms lend themselves to an easy extraction process, while others require more difficult procedures to extract the DNA.

DNA is a nucleic acid located in the cell’s nucleus. It is found making up the chromatin in which it is bound to several types of proteins. The nuclear and the cell membranes are a tough protective barrier, made of lipids and proteins, they need to be eliminated in order to release the DNA. It is very important that the directions be followed carefully to ensure good results.

MATERIALS PER GROUP

(**indicates how the stock solution is prepared**)

  1. 1 cup with 10ml of clear Gatorade or .9% salt solution.
  2. 2 small beakers
  3. 2 test tubes
  4. test tube rack
  5. stirring rod
  6. transfer pipette
  7. microscope
  8. microscope slide and cover-slip
  9. 10ml ICE COLD 95% ethanol
  10. 10ml Extraction Solution (E sol.)

(** 10ml detergent, 10g NaCl, 1g meat tenderizer, 90ml H2O**)

  1. 25ml 5% salt solution (**5g NaCl, 100ml H2O**)
  2. Methyl Blue

PROCEDURE

  1. Label the beakers:
  • Ethanol
  • E. Sol.

and one test tube:

  • NaCl Sol.
  1. Fill each beaker with 10ml of each of the solutions.
  1. Put at least 10 mL of water in your mouth and swirl the water around vigorously for at least 30 seconds. Spit the water back into the plastic cup.

The swirling of the water washes cells from the inside of your cheeks into the water

  1. Transfer 3-4ml of the cheek-cell water, very carefully, from the cup into a clean test tube, Add 20 drops (about 1ml) of E sol.. Swirl or stir the test tube very carefully to mix.

The meat tenderizer will denature any protein that will contaminate the DNA and the detergent will break open the cell membranes.

Continued on back

  1. Carefully pour 5ml of ice cold ethanol down the side of the test tube to form a layer on the top of the cheek cell mixture. Let stand for a minimum of 3 minutes.

**You should start to see the DNA rise into the ethanol layer. It looks like mucus and usually has some air bubbles trapped in it.

  1. With a twirling motion of the glass rod, slowly move it through the interface (where the two solutions meet) of the two layers. Collect the mucus-like DNA and place it in a test tube containing the 5% salt solution.
  1. Add 1-2 drops of methyl blue stain to the DNA solution. Stir gently and let it stand for about 3 minutes.
  1. Collect the stained DNA and place on a clean slide. Cover with the cover-slip.
  1. Observe under 40x, 100x and 400x. Under 400x a super coil of DNA could be visible.

QUESTIONS

  1. What was the purpose of having detergent in the Extraction solution?
  1. What steps were undertaken to eliminate any protein contamination in the process?
  1. Methyl blue bonds with nucleic acids and turns them a blue/purple color upon contact. What type of molecule is DNA?
  1. What is the function of DNA in the body?
  1. How does DNA work with mRNA and tRNA to accomplish its function?
  1. Using the genetic code, what three amino acids would the following DNA strand code for? 3’ T A C G G A T A G 5’
  1. Describe the structure of a DNA molecule (in words) and sketch a drawing of the molecule.
  1. What is base pairing?
  1. What are similarities and differences between the structure of DNA and RNA?
  1. What is DNA polymerase? What is RNA polymerase? Describe the differences in each of their function.
Top View