Broccoli DNA Extraction
Materials needed:
broccoli, distilled water, scissors, detergent, ethanol, sodium chloride (salt), sieve, mortar and pestle, electronic scale, pipette, petri dish, 2 beakers
Experiment date: 9/22/23
Written by: Sophia Han
Step 1
Add 2g of sodium chloride in 150ml of distilled water and stir it with a pipette (you can use a stirring rod as well) until it dissolves.
Then, add 7ml of detergent into the solution and mix it with a pipette once again.
Step 2
Cut out 50g of broccoli with scissors (you can also use a cutter knife) and grind them using a mortar and a pestle.
Step 3
Put the ground broccoli into the solution (the one with distilled water, sodium chloride, and detergent) and mix it with a pipette (mix it enough so you can get an accurate result).
Step 4
Using a sieve, filter out the 'broccoli mixture' into another beaker (try not to get any broccoli or bubbles into the beaker).
Step 5
Slowly pour ethanol (has to be cold ethanol) onto the filtered solution and observe what happens.
Discussion
Results:
The DNA moves up to the surface (towards the ethanol). The longer you wait, the more visible the DNA threads become.
How did this happen?
Unlike animal cells, plant cells have a cell wall surrounding the cell membrane. It is only when the cell wall is destroyed physically that the DNA can escape from the cell, which is why we had to grind the broccoli into smaller pieces. Similarly, detergent is required for the DNA to be released. Detergents are made of molecules (called surfactants), in which the head is hydrophilic (i.e., attracted to water; water-loving) and the tail is hydrophobic (i.e., repels water; water-hating). The detergent binds to the hydrophobic end of the cell membrane and separates the head, hence breaking the cell membrane.
When dissolved in water, sodium chloride, better known as salt, is divided into sodium ions (Na+) and chloride ions (Cl-). By adding ethanol, the sodium ions (cations=positively charged ions) combine with the DNA (anionic nature=negatively charged). This causes the DNA to become white in color and to join together.
Ethanol decreases the solubility of the DNA and makes it visible to the eye in the ethanol layer. By using cold ethanol, it reduces any damage inflicted on the DNA and helps with its condensation.
What exactly is DNA?
The DNA, the abbreviated form of deoxyribonucleic acid, is a molecule carrying the genetic information of an organism. It is present inside the nucleus of a cell and is made up of two long chains of nucleotides, formed into twisted strands to make a helix. A nucleotide consists of 4 bases, adenine (A), thymine (T), cytosine (C), and guanine (G), along with a 5-carbon sugar molecule and phosphoric acid. While the phosphate and sugar molecules stay the same throughout the chain, the bases can be any of the four. It is the chemical bonds between these bases that hold the two strands together (A is always paired with T and C always pairs with G).
