Investigation: DNA Extraction (AP Bio)

Strawberries are a favorite specimen for DNA extraction because they are octoploid, which means they have eight sets of chromosomes. The procedure for extracting DNA from a strawberry is simple, and the results are usually obvious, it is easy to see the white strands of DNA within the pink solution of strawberry juice.  The same technique can be used to extract DNA from other samples.

Experimental Question: 

How can DNA extraction techniques be used to compare DNA content of cells from different samples? Do some samples have more DNA than others?

Objectives

• Extract DNA from a living specimens using household products
• Compare the amount of DNA  in each specimen
• Suggest reasons for differences in DNA amounts.

Materials and Procedure

• DNA Extraction Buffer:1000 ml of deionized water,
  50 ml of clear dish detergent, 1 teaspoon of salt
• Living samples  (peas, strawberries, kiwi, grapes, bananas, beans)
• Ziploc bag
• Straining equipment (coffee filters, tulle, kitchen strainers)
• Funnel
• Test tubes collect filtrate
• Ethanol or 91% isopropyl alcohol (chilled)

1. Add sample to a Ziploc storage bag.  

2. Add about 10-20ml of the DNA extraction buffer and mash sample and buffer for about one minute. 

3. Use a funnel and strainers (or coffee filters) to filter the mixture into a beaker or test tube. 

4. Slowly pour or drip cold alcohol over the top of the filtrate.  You want a single layer.

5. White strands will form in the ethanol layer, use a stirring rod or toothpick  to spool the strands. 

Lab Report

1. Introduction
   - include background information and purpose of the experiment
   - should include a CLAIM that answers the experimental question

2. Data and Observations 
   -include descriptions or photos of your observations
   -compare samples

3. Analysis
   -answer the experimental question, providing citing EVIDENCE that supports the claim from your observations
   -use REASONING to suggest reasons why there are differences in the amount of DNA (cite sources)

4. Discussion (can include any or all of the following)
   -include personal reflections about the experiment
   -suggest how you could improve the design or discuss errors in your experiment
   - propose new experiments about DNA or extensions to this one (what else would you like to learn?)

Other Resources on DNA

DNA Extraction for Freshman - a simpler version of this activity, uses only strawberry

DNA Extraction from Saliva - rinse your mouth and discover DNA!

Coloring DNA – basic image of DNA and RNA for students to color following directions; includes questions and analysis

Transcription & Translation Coloring - shows structures involved, nucleotides, base pair rules, amino acids

DNA Concept Map - design a concept map showcasing the structure and function of DNA

DNA Models - students can examine 3D models of DNA to understand the structure

Construct a Paper Model of DNA - cut and paste nucleotides