MadSci Network: Molecular Biology

Subject: How are the DNA molecules arranged after an extraction lab?

Date: Fri Nov 5 18:26:21 1999
Posted by Lisa Hughes
Grade level: teacher/prof School: Bayside High School
City: Palm Bay State/Province: FL Country: U.S.How are the DNA
Area of science: Molecular Biology
ID: 941844381.Mb

After performing an extraction lab from calf thymus, the DNA was visible 
as strands as long as 2 meters hanging from the inoculating loop.  Are 
these multiple DNA molecules stuck together vertically to make them so 
visible to the naked eye?  When the DNA is precipitated in the ethanol, it 
forms 2 layers with the DNA settling in the bottom layer.  Is this bottom 
layer also where the ethanol is as my understanding is that the DNA is not 
soluble in the ethanol so that's why it clumps together in it and the rest 
of the cell parts are left behind in the water layer.  Is this right?

In response to the clarifications you requested.

1.  Yes, I mean 2 meters.  It was amazing.  My tallest student was holding
the strand above his head and it reached to the floor.

2.  The lab extracted the DNA from calf thymus.  It began with the addition
of a prep buffer (epsom salt, buffered aspirin, sucrose and distilled water)
and a detergent solution.  After that, some NaCl solution was added.  Then it
was centrifuged and finally a layer of ice cold ethanol was poured on top.
It was the ethanol that caused the DNA to precipitate out of the solution.
If you happen to know what the pellet consisted of after the centrifuging,
that would be great, too.  I am assuming it was the heavier of the cell
parts.  By the way, the buffer was used to both neutralize the negative
phosphate charges on the DNA and also to slow the enzymes down to avoid
shearing.  Thank you in advance for your help.  I do this lab every year but
am always frustrated by the questions my brilliant students ask.

Lisa Hughes

Re: How are the DNA molecules arranged after an extraction lab?

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