DNA Extraction Activity

Why extract DNA from a…….? Demonstrate that food actually has DNA in it! One study showed that some people think that traditionally bred plants DON’T have DNA while biotech- developed plants do Show that DNA is a physical entity that can be analyzed, cut into pieces and “reassembled” People have a hard time “visualizing” DNA. This makes it very difficult for them to understand how transformation works, etc. Demonstrate that DNA from various sources looks the same Important to understand that, even though DNA comes from different species, it has the same basic makeup (bases, base-pairs, etc.) Use as an attention-getting activity and to increase participant involvement

DNA Lab objectives Life Science The cell - DNA is located in the cell nuclei of all living organisms Molecular basis of heredity - DNA molecule directs the synthesis of every protein and contains all the genetic information that is passed on to new cells. Physical Science Chemical reactions - structure of cell membrane Science as Inquiry Design and conduct scientific investigations Formulate and revise scientific explanations and models using logic and evidence

Cell membrane Cytoplasm Nuclear membrane Proteins To Extract DNA, You Must Remove … Three Main Steps in Any Extraction  Break apart cells  Release DNA from nucleus  Precipitation of the DNA

To extract DNA from a strawberry, have each team…. 1. Put a #2 coffee filter over the top of a 5 oz plastic cup to create a funnel. Fold the edges of the filter down to secure it to the cup. 2. Place ¼ - ½ strawberry in a 1 quart Ziploc bag. Crush the strawberry by repeatedly squeezing the bag. 3. Pour 15 ml of the soap solution into the bag with the strawberry. Squeeze the bag until only very small pieces of strawberry remain in the soap solution. 4. Pour the “mashed strawberry mix” into the coffee filter funnel. The liquid part of the strawberry-detergent mix will pass through the filter and into the bottom of the cup Step #:

5.Remove the filter and discard. Pipette 1 ml of the strawberry-soap solution (filtrate) from the bottom of the cup and carefully pour it down the side of the test tube containing the alcohol. 6. Cap the tube and gently rock the test tube from side to side (Don’t shake it). Bubbles and white, cotton-like strands should begin to rise toward the top of the alcohol. This is the DNA. 7If desired, use the tip of the pipette to remove the “glob” of DNA from the test tube. To extract DNA from a strawberry, have each team… Step #:

Why Detergent? Detergent dissolves the lipids in the cell membranes and nuclear envelope Soap molecules and the lipids (fats) in cell membranes are made of two parts: membranes are made of two parts: hydrophillic heads hydrophobic tails When detergent comes close to the cell, it captures the lipids and proteins (due to their similar structures)

Why Ethanol or alcohol? The addition of the cold alcohol precipitates the DNA since it is insoluble in high salt and alcohol. Since water is soluble in ethanol, the water becomes dissolved into the comparatively large volume of ethanol, which effectively removes the water from around the DNA—causing the DNA to precipitate. Salt stabilizes the negatively charged phosphate groups and allows the DNA strands allows the DNA strands to clump together. DNA has a negative electrical charge due to the phosphate groups on the DNA backbone, and the electrical charge makes it soluble. When salt is added to the sample, the positively charged sodium ions of the salt are attracted to the negative charges of the DNA, neutralizing the electrical charge of the DNA. This allows the DNA molecules to come together instead of repelling each other. Why Salt?

What happened? Squashing the strawberry broke down the cell walls The shampoo broke down lipids in the cell walls As a result of both actions, proteins, DNA and other cell material were released Filtering the solution removed the larger material When the filtered solution was poured into the alcohol, the DNA precipitated (as well as some other material), forming a cotton-like mass.

Discussion Questions Where can DNA be found in the cell? What is DNA? What are the three basic steps in any DNA extraction? What is the purpose of the detergent? Of the sodium chloride? Of the alcohol? Describe the appearance of your final product. Is this a pure DNA sample? List some practical applications where extracting DNA is necessary.