Why is there a difference in the consistency of the DNA between a ripe and an unripe banana?

Question

I am asking this question on behalf of my son who is in 4th grade and he did a science experiment where he extracted DNA from a variety of fruits when they were unripe and when they were very ripe. With the ripe banana DNA it was amazing - so clumpy it stuck to the sides of the test tube and he was able to scoop it out with a fork. For the unripe/green banana, it seemed that the same amount of DNA was extracted and it seemed to gather together the same, however, it was thinner and when he tried to scoop it out of the test tube it just fell through the fork. We are wondering why the DNA of the unripe banana was so much thinner and why the DNA of the ripe banana was thick and clumpy? What's the difference? On a side note - strawberry and kiwi DNA looked exactly the same between ripe and unripe fruit. With this experiment he won at his class level and is competing at the school level next week. Wish him luck!! Mom

Answer 1

Mitosis is the reason.  Mitosis is the process

in which the dna in a cell replicates itself

before the cell. divides into two daughter cells.

Due to mitosis the number of cells in the fruit,

and thus the dna, is doubling at a steady rate.

The ripe banana has more dna than the unripe

banana because mitosis has been occurring

longer in the ripe banana.

 

Mitosis is how people with burn injuries

can heal.  Google "mitosis" for further

information. 

 

Good luck.  :-)

Answer 2

Dear Mary

 

I do not know how your son extracted DNA, did he use kit? 

 

Unfortunately, mitosis is not the right answer here.

 

DNA from the ripe banana is in fact glycosylated, the extraction method did not get rid of all the sugar in ripe banana. It has remained clumped with DNA.

 

He may heat the DNA at 37C water-bath over night and reprecipitate it with ethanol. That might get rid of some sugar. 

 

In the lab, we soaked tiny pieces of mice tails over-night in buffer at 37C to break proteins for clean DNA extraction/isolation.

 

Hope this helps, please let me know the results and his thoughts.