What is CRISPR SYSTEM?
CRISPRSYSTEM was first found in bacterial cells or in prokaryotic cells CRISPR
SYSTEM is like a type of immune system in these bacterial or
prokaryotic cells so it's a region on the bacterial genome so
this is called the CRISPR and Marcus
CRISPR locket from its name is
clustered regularly interspaced short palindromic repeats what does that mean
so the CRISPR locus is a repeat of
DNA so like this is this sequence is exact these sweet Pete's are first of all
shores.
Palindromic sequence in CRISPR
SYSTEM
Secondly or palindromic and what's palindromic
means is that if you read them from left to right or from right to left you end
up with the same sequence and they are received in regularly interspaced it
means that they there are space your DNA between them and these spacer DNA's
are regular so it between each two-plus and crisper air repeats there is a DNA
spacer so the CRISPR locus is DNA or
a piece with space of DNA in between so this is what we call the CRISPR lockers CRISPR quick the lipids are ephemeral between it is between 28 and
37 base pairs in length and the space of DNA is between 32 and 38 days.
Working
principle of CRISPR SYSTEM
The bacterial cell there is something called B bacteria phages. Bacteria phages are viruses like this it's virus and this virus can infect the bacterial cells how does the bacteria phage infect the bacterial film? the bacteria stage invade the bacterial cell if it attached itself on the bacterial surface and then it injects its genome inside the bacterial cell so this is the viral genome now this viral genome will force the cells to produce the viral proteins and the viral enzyme and then it will change the whole-cell machinery in the bacterial cell and this is how the bacteria phage invade or infect the bacterial cell. Now the bacterial cell because a CRISPR SYSTEM can like it can prevent this to happen a second time so the CRISPR SYSTEM is somehow like the adaptive immune system in human so it's a kind of memory it's a kind of memory to prevent the same bacteria phage from infecting this gel and other times.
Mechanism of CRISPR SYSTEM
The CRISPRSYSTEM is a three steps mechanisms the first is the space your
acquisition. The first step is a spacer
acquisition then have the quick-drying and processing and then have the interference
these are the three steps of the CRISPR SYSTEM.
Spacer acquisition
This
acquisition step is the same in the three different types of CRISPR
SYSTEM. There are three types so
· Bacterial cell surface
·
Bacteriophage
·
Bacteria phage
The viral
genome and this is the CRISPR locus
so what's going to happen is that when the bacteria phage infected cell person
for the first time, the bacterial cells chop up the viral genome and take a
piece of it and insert this piece into the G and a space of DNA so what you
should know is that space your DNA's is nothing but pieces of different buyer
viral genomes that have infected the cells previously so each time about a
bacteriophage insects this cell to cell take a piece of it and insert it into
the spatial DNA. the CRISPR locus
there are the gaps inside this cat's genes which is the cast enzyme the cap
enzymes are many enzymes that are implicated in the clear in the crystal process
the café's lines in general are most of them are nucleases or helicases to
understand this so let's imagine this is a this is the DNA sequence nucleus can
pop the DNA in this way it cuts the link between the nucleotides where is
Henrique’s can cut the hydrogen bonds between the two strands and then it can
separate the two strands of DNA from each other most of the cap enzymes are
nucleus of any helicases in the fifth position we have two main players we have
cash flow and cash - both of them are diamonds there- form that is form
conflicts to get a Catholic a student conforming complex together in order to undergo
spacer
acquisition.
Step 1:
There are three types of CRISPR SYSTEM type one two and three
have the same spatial acquisition step gas form is a nucleus can behave nucleus
and integrate activity so it can cut the viral genome and integrate the piece
of genome in the spatial DNA whereas capture is in the ribonuclease so some
bacterial pages have RNA genome so this here this bacterial page has DNA genome
but other viruses have has RNA genomes so castor is an endoribonuclease.
Step 2:
Now the second step
which CRISPR RNA is processing. rRNA is CRISPR RNA processing now we have this CRISPR largest we have different pieces
of bacteriophages genomes in the spacer DNA what's going to happen now is that
one of the two strands of DNA is going to be the transcribed into messenger RNA
now this messenger RNA is exactly complementary to this trend and it's complimentary
to the lower strand and in this case, we call the lower strand decoding turn
because if this trend that was transcribed to a messenger RNA now this Matthews
RNA as complementary to the lower sense which contains complementary sequences
from the CRISPR repeats and the viral
genome sequences.
Creeper repeat loops:
The Creeper repeat loops are looked like this
they form loops and then the messenger RNA will be cut using gas 6e or caste 6f
enzyme the messenger RNA this sequence is going to be chopped up like this so
we will end up with small pieces of RNA each piece contains the CRISPR sequence which forms a loop empty viral the piece of the
viral genome.
CRISPR RNA:
these small
pieces are the CRISPR RNA this is a
platform in fact - so we have another player in this CRISPR processing it's called the tracer RNA there are these pieces
of RNA which are bound to the to the CRISPR
sequences on the messenger RNA so this star is called the trace or RNA trace.
the TRA is from trans activating tra CR is from CRISPR and RNA these pieces of RNA bind to the CRISPR repeats on the messenger RNA and then the messenger RNA will
be chopped out by cast 9 and another enzyme called RNA s 3 and we'll end up
with these pieces of RNA so in this case you have the CRISPR repeat we have the viral the piece of the virus genome and
the tracer RNA together and these are the whisper RNAs in type 2 type 3 is very
simple so type 3 cast 9 homolog is going to chop up them and message or
indirectly and we will end up with the quiz for RNA containing the CRISPR repeat and the piece of the viral genome.
Step 3:
The interference
which is also different between the three types of CRISPR SYSTEM but in
general the CRISPR RNA will be integrated with the cap protein to end up with
the conflicts containing the caps proteins with a piece of RNA inside which is
decreased for RNA this is, in general, this is the interference the interference
is between the Cal specific tasks protein and RNA sequence they are going to
Mir to be merged together to form this complex now the differences between the
three types let's go to task one in fact one
we have the CRISPR sequence is looped then then
what's going to happen is that when this when the stage when the bacteriophage
infects the cell and all the time so as I told you in the bacteriophage
infected this the cell the first time this beach was taken from this state and
now when this page comes another time to infect this bill this piece of RNA can recognize this piece of
DNA because it's complimentary
Pam sequence:
There is a
very important player in type 1 and type 2 which is this
yellow sequence here it's called with Pam and Families protospacer their
adjacent motive what is the tablet let me tell you a little bit about the time
because it's important scientists have found that when – like when the
bacterial cells choose a piece of the viral genome to take it doesn't take just
any piece of the viral genome it takes the piece of the viral genome which is
adjacent to the Pam sequence so the
bacterial cells can recognize the Pam
sequence and then it takes the adjacent seeker in order to add it into the
space your DNA and then in order to form the CRISPR RNA and the CRISPR
complex from it why the time is important because the cast enzyme can recognize
the time sequence so here we increase the specificity because not only the RNA
sequence can recognize the DNA sequence here but also the cast enzyme can recognize
the time sequence here and in this case we are increasing the specificity of
recognition tom is very important in type 1 and type 2 but noting type 3 so
what's going to happen here is that the
casts enzyme will recognize the Pam
sequence and then the RNA sequencer is going to recognize the adjacent
sequence here which is exactly complementary to this sequence so it's going to
happen if that be the viral genome will bind to the R and H like this - the
complementary strand because this is complementary and then the viral genome
will bind the lower strand was copied so the lower strand is complementary to
this and then the lower strand will bind to the RNA sequence.
Types of CRISPR SYSTEM
CRISPRSYSTEM has three types depending on the bacterial cells
I.
CRISPR SYSTEM type 1
II.
CRISPR SYSTEM type 2
III.
CRISPR SYSTEM type 3
CRISPR
SYSTEM type 1:
type 1 when
this binding happens this will activate a cascade of cat enzyme so many gas enzymes will be
activated and it's very complicated actually no one exactly knows the process
until now but at the end this gas cascade will recruit we recruit Castries to
chop up the viral genome like this so in type 1 gas 3 will chop up the or on
will cut the viral genome to end up with a liquid degraded viral genome so the
virus cannot invade the cell anymore this virus in us cannot infect the cell
anymore this is a platform in type 2.
CRISPR
SYSTEM type 2:
type 2 isn't
the most important in fact to the main player is cast 9 so before the time
sequence is also important in type 2 because cast 9 enzymes can recognize the
time sequence and then this RNA sequence can recognize this DNA sequence and
then they will bind together to form like the RNA is complementary to the lower
strand and then they will bind together and then this cast enzyme itself will undergo
something called the doubles strand break in the viral genome and what double
strand break means is that the cast
enzyme will break the two strands exactly at the same place it's called a
double-strand break the cast enzyme has two domains so this is what we end up
with the viral genome will be chopped up the capping enzyme has two domains called
the air HMC and they are like RNase H
like in the nucleus domains and the
cache enzyme can use these two domains in order to do this double-strand break
this is type 2.
CRISPR
SYSTEM type 3:
Type 3 is very
simple also there is a CAF enzyme there is no pam here in fact 3 so the RNA sequence
we recognize it's complimentary here on the viral genome and then they will bind
together and there will be also a cascade of cache enzymes like type 1 and then
the viral genome will be chopped up.
Conclusion:
system is a
three-step system the first step is special acquisition in which the bacterial
cells took a piece of the viral genome which invades the bacterial cell for the
first time and if it is too great this sequence into the spacer DNA so we will
have several pieces of different viruses into the spacer DNA's then in the
crystal RNA processing this strand will be copied to the messenger RNA and then
the messenger RNA will be chopped up to give the twist paralanguage contains a
complementary to the piece of crystal speed and the piece of viral genome and
in the third step the interference this CRISPR
RNA will be merged with the cast enzyme to form this coke like and then when
the viral when the same virus will invade the cell or will try to infect this cell another time this
cast enzyme and the piece of RNA will recognize the complementary Spiece here and this will cause the
chopped-up in the viral genome.
