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Semiconservative Science Dude

by Greg Crowther and J.P. Taylor


This is a musical summary of Meselson & Stahl's 1958 paper (Proc. Nat. Acad. Sci. 44: 671-82) in which they established that DNA replicates by a "semiconservative" mechanism.

A more detailed but very readable account of Meselson & Stahl's experiments may be found in the 4th edition (and perhaps subsequent editions) of Stryer's Biochemistry textbook.


I'm a semiconservative science dude;
I only trust data that are peer-reviewed.
But based upon empirical observation,
I believe in DNA replication.

My name is Franklin Stahl; I study DNA.
That's our genetic code. (Yes it is, yes it is.)
And what I want to know about our DNA
Is how it replicates inside a cell.

So here's what I will do: I'll grow some E. coli
And feed it N-15. (Yes I will, yes I will.)
And when those little bugs are full of N-15,
Their DNA will weigh more than it should.


So what will happen now if we switch to N-14
And let the cells divide (only once, only once)?
The daughter DNA inside each daughter cell
Is neither heavy nor light; it's in between.

Can you guess what occurs when the cells divide again
And make more DNA? (Can you guess? Can you guess?)
The new cells' DNA is different from before --
Half is of medium weight, and the other half light.


The data we've discussed confirm beyond a doubt
What Crick and Watson said (what they said, what they said).
The parent DNA is not conserved as is;
It's split between the pair of daughter cells.

So in each daughter cell, the DNA is mixed:
Half old and half brand-new (half and half, half and half).
In scientific terms, this replication scheme
Is "semiconservative" -- that's what it's called.


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