Real Science and Other Adventures

CRISPR-Cas9 genome editing – answers

Last time we looked at CRISPR-Cas9 genome editing and I asked a couple of questions.

  1. How would the bacteria be able to make a specific “guide RNA” that matches a piece of viral DNA? (Hint – how is RNA made?)
  2. You want to use CRISPR-Cas9 to do some genome editing. Why do you need to design the guide RNA you are going to use?

These are my answers:

  1. RNA is made by transcription – it is copied from DNA. So the bacteria must have bits of viral DNA in their genome. This discovery of viral DNA in a bacterial genome was what led Fransisco Mojica to guess (propose a hypothesis) that this was a type of immune system against viruses.
  2. The guide RNA needs to match the DNA you want to cut. So you need to find out the sequence of the DNA you’re editing and design a matching RNA sequence.

A guide RNA sequence is complementary to the DNA strand it will bind to. But note that it is the same as the opposite DNA strand, except that RNA has a U where DNA has a T.


The story of CRISPR-cas9 research: This is the human story behind the discoveries, and was published in the scientific journal Cell. This is a timeline of the research. It starts with a chance observation made during basic research, and leads to using the results of research from different labs over several years for a specific purpose.



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This entry was posted on January 31, 2016 by in DNA tools and techniques, VCE Biology and tagged , , , , .
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