DNA extraction
DNA is found in the nuclei of eurkaryotic cells
Eukaryotic cells like animal and plant cells contain their genetic material inside the nuclei of cells.
DNA is wrapped around organising proteins called histones to form structures known as chromosomes.
In order to extract DNA from strawberry cells successfully, it requires a number of steps. You may refer to the protocol at the end of this page if you want to try your own DNA extraction at home.
As DNA is located inside the nucleus, it needs to be separated from the histone proteins and released from the nuclear membrane. Additionally, the cell wall and the cell membrane must also be removed in order for DNA to be isolated properly.
big vs small fruit
Click here to read up on the different species and hybrids of strawberry plants.
Strawberry plants exhibit this condition known as polypoidy, where the nucleus can contain multiple sets of chromosomes.
Polypoidy is a result of whole-genome duplications, and has the potential to contribute to novel phenotypes.
underneath the sepal
After carefully removing the sepals of the strawberry fruit, take a closer look!
Fruits develop from flowers that are successfully pollinated.
The stamens (anther & filament) are usually still present underneath the sepals in strawberry fruits.
polypoidy
Some strawberry species can be decaploid. This means that the strawberry genome contains 10 sets of chromosomes.
That is a lot of DNA! Thus making them suitable specimens for DNA extraction as they have a high yield of DNA.
precipitation of DNA
The addition of ice cold ethanol to the strawberry mixture causes DNA to precipitate out of solution.
The DNA molecules are the white strands that form between the interface of the two liquids.
isolated DNA
DNA that has been precipitated out of solution can be removed by twirling it around a glass rod or satay stick.
This isolated DNA can be redissolved in distilled water. pH indicator can be added to determine the pH of DNA.
pH of DNA in solution
DNA extraction from strawberries was an old protocol that I tried with students from my previous school too. My three ex-students show you the results they obtained after adding a few drops of universal indicator into their DNA sample dissolved in distilled water.
Suggest an explanation for each of their results.
Hardworking and meticulous, Caleb makes an effort to follow the steps of his protocol exactly.
pH indicator reads RED.
remarks: well done!
pH indicator states that DNA in solution is strongly acid.
The phosphate groups in the DNA molecule tend to deionise and lose H+ ions to the surrounding solution.
When the pH indicator was added, the large amounts of H+ ions in solution caused the indicator to turn RED.
Intelligent, yet slightly complacent, Shaun may attempt to skip or modify certain steps in the protocol to finish his experiment more quickly.
pH indicator reads ORANGE.
remarks: relatively well done.
pH indicator states that DNA in solution is acidic.
This observation implies that there was slight detergent contamination in the DNA sample.
As the phosphate groups in the DNA molecule deionise and lose H+, some of these H+ were used to neutralise the detergent contaminant. The remaining H+ that were not used in the neutralisation reaction remained, thus causing the indicator to turn ORANGE.
Amiable, but a little aloof, Chien Lun sometimes struggles to follow protocol and has the tendency to accidentally add wrong volumes of solutions or completely skip certain steps.
pH indicator reads BLUE.
remarks: room for improvement. =(
pH indicator states that DNA in solution is alkaline.
This observation implies that his DNA sample he extracted was contaminated with large amounts of alkaline detergent solution (that was previously added), resulting in the BLUE colour when universal indicator was added.
Protocol for DNA extraction from strawberries
Place 1 strawberry into the mortar and pestle and add 10 cm3 of detergent solution.
Pound the strawberry to break up the cells and nuclear membranes to release the DNA.
Pour (decant) the fluid into a clean boiling tube.
Add 3 - 4 drops of meat tenderiser solution to denature any proteins bound to the DNA. Mix well and leave the test tube to stand for a few minutes.
Carefully pour 10 cm3 of ice-cold ethanol down the side of the boiling tube to form a layer on top of the strawberry mixture. Let the mixture stand for 3-5 minutes.
Using a twirling motion, slowly move the end of the glass rod through the interface of the two layers (area between the ethanol and strawberry mixture). You will see some white translucent strands. These are DNA strands.