16. Microbial Genetics
16. Microbial Genetics
Play a video:
Was this helpful?
in this video, we're going to begin our lesson on the CRISPR CAS system. And so the crisper cast system is really in its natural state. A bacterial cell defense mechanism against various fage infections. And so the CRISPR CAS system is used by bacteria to defend or protect themselves against viruses, bacteriophages or phages that are capable of infecting them. And so CRISPR is actually an acronym that stands for clusters of regularly inter spaced short palindrome IQ repeats. And so you can see these letters here is where the crisper acronym comes from. And so really this is just a description, a detailed description of a specific region in the bacterial cells chromosome. And so the way that this CRISPR caste system works is that it protects the cell from infections that it once encountered. And it does this by storing small pieces of fage D. N. A. In its chromosome. And these small pieces of DNA that are stored in the chromosome are referred to as spacers. And so really what happens is upon the first fage infection, the first time a cell is encountered by a fage, it's possible that a protein complex within the cell degrades the fage D. N. A. Into small fragments and then those fage D. N. A fragments are sometimes capable of being incorporated into the chromosome as a spacer. And so these spacers within the bacterial cells chromosome really serve to act as a record of previous fage infections. And so what happens is during any subsequent fage infection, like for example a second infection by the same virus, the cell is able to transcribe those space or fragments of various fage D. N. A. And those transcribed RNA. S. That are really just from fage the fage spacers. They end up forming a complex with another enzyme within the cell called CASS. And so the Cast forms a complex with the R. N. A. And so it forms a Cast RNA complex. And this cast RNA complex is capable of targeting the infecting fage D. N. A. And it's able to cut it in order to inactivate the fage. And so ultimately this Cast RNA complex. This CRISPR caste system is all designed to protect and defend the bacteria from fe ages by inactivating the pages upon subsequent infections. And so this CRISPR CAS system because um it is being incorporated into the chromosome that means that it can also be passed down to future generations of bacteria. And so the future generations of the bacteria will also be able to protect themselves against those same viruses. And so if we take a look at our image down below we can get a better understanding of the CRISPR CAS system. And so what you'll notice is over here on the left hand side this is representative of the very first fage infection. And so um what you'll notice is that in this very first page infection you have the bacteriophage virus that's inserting its genetic material. However in some cases the genetic material of the fage the fage DNA that's being injected can be degraded and cut up into small fragments and then those small fragments can be incorporated into very specific regions of the chromosome. And so this is what we get. Uh this is where the spacers come from. And so the spacers are represented by these different colored regions that you see down below here and it's really just a zoom in of a very specific regions of the chromosome. And so these spacers serve to act as a record of previous fage infections. Since little tiny fragments of fage D. N. A. Are incorporated into the chromosome as spacers. And so um after the uh fage D. N. A. Is incorporated into the chromosome, the fragment of the D. N. A. Is incorporated into the chromosome. Then upon a second infection upon a second viral infection. What happens is uh this CRISPR system including the cast jeans and the spacers are going to be transcribed. And so it forms this RNA. A molecule here and the RNA molecule forms a complex with this cast enzyme. And so what you get is a Cast RNA a complex. And this cast RNA complexes capable of protecting the cell against subsequent infections protecting the cell from a 2nd and 3rd viral infection. And so the cell is protected from a second fage infection using the CRISPR CAS system. And so what you'll notice is uh the fage when it does infect for a second time, it injects its genetic material uh injects the infecting D. N. A. P. H. D. N. A. And what happens is the the crisper system. Okay which again is in this specific region it gets transcribing, it's activated and it forms this Cast RNA complex. And what happens is this Cast RNA complex is capable of targeting the fage D. N. A. And inactivating it cleaving it to inactivate it. And so really what happens is the RNA that's in the cast complex acts as a guide. And so its sequence here is complementary to a sequence in the fage D. N. A. And so it guides the cast enzyme to the fage D. N. A. And the cast is capable of cleaving and inactivating that fage D. N. A. And so the fage D. N. A. Is degraded by the Cast RNA complex. And what that means is that the bacterial cell now has a defense mechanism against this specific fage. And so it's protected against subsequent infections by this fage. And so once again because the crisper system is part of the chromosome it can be replicated and passed down to future generations of bacteria as they replicate. And so the defense mechanism against this particular fage is going to be passed down to future generations. And so this year concludes our brief lesson on the crisper cast system and how it serves as a bacterial cell defense mechanism against fage infections. And so we'll be able to get a little bit of practice on these concepts as we move forward in our course. So I'll see you all in our next video.
What is CRISPR?
Sequences of bacterial DNA derived from viral DNA fragments.
A gene editing tool.
A bacterial defense mechanism against viral infections.
All of the above.
The enzyme which targets phage (viral) DNA and destroys it before it can infect the bacterial cell is known as?