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Last Friday, we had another in the series of weird DNA structures. (You can see the first here).

I asked the audience to identify the unusual feature in this molecule. Here’s the first picture:


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Here’s the answer:

Steve L. guessed it correctly. This is not just DNA, it’s a DNA:RNA hybrid. I circled a 2′ hydroxyl group here to make it easier to see the difference. (Remember – the “D” in DNA stands for “deoxy.”) The oxygens are red and it’s easiest to tell the difference between the strands if you count them.


For extra credit – where might you find this kind of thing in nature?


  1. #1 G Barnett
    August 3, 2007

    Where in nature? During DNA transcription for protein production, I’d think. DNA strand splits apart, RNA forms up until the code for a protein has been copied over, then it heads off to manufacturing.

  2. #2 Sandra Porter
    August 3, 2007

    yep, you win!

  3. #3 qetzal
    August 3, 2007

    Also during DNA replication. DNA polymerases generally can’t start new strands. They can only extend from the 3′ end of an existing strand, called a primer. Primers are generally made of RNA (because RNA polymerases can start new strands).

    Also also, during reverse transcription to convert an RNA virus into a DNA provirus.

  4. #4 PeteK
    August 5, 2007

    And in retrovirues etc …

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