CRISPR-Cas Flashcards
who wont the 202 nobel prize for the discription of CRISPR-Cas system
Nobel Prize Chemistry 2020 for CRISPR-Cas - Jennifer Doudna (left) and Emmanuelle Charpentier (right) shared the prize
what is CRISPR-Cas
Clustered Regularly Interspaced Short Palindromic Repeats & CRISPR-associated genes - a segment of DNA containing short repetitions of base sequences, involved in the defence mechanisms of prokaryotic organisms to viruses.
where are the CRISPR sequences derived from and used for
are derived from DNA fragments of bacteriophages that had previously infected the prokaryote.
used to detect and destroy DNA from similar bacteriophages during subsequent infections.
what parts of the CRISPR-Cas system were found in 1987
in 1987, found homologous sequences as direct repeats in bacterial dna along with spacers
the CRISPR system is found in what percentage of bacteria and archaea
~50% of the Bacteria
~95% of the Archaea
how many of the spacers have sequences of known viruses or plasmids
Only 10% of the spacers give BLAST hits with known viruses or plasmids
(untapped reservoirs of virus diversity and virus-host interactions)
what are the 2 classes of CRISPR-Cas systems
class 1; type 1 3 and 4 class 2: type 2 5 and 6
what are the sequences present in the CRISPR-Cas sequences coding for
pre-crRNA processing effectors molecules target cleavage spacer insertion regulation domain helper
what is the main difference between the two CRISPR-Cas systems
main difference between the two classes is their effector molecules: Class 1 effectors contain multiple subunits while class 2 effectors are single large proteins
describe CRISPR immunity
New phage enters, injects its DNA. DNA is degraded upon entry and the loose info is bound by Cas1 and Cas2 and added to the CRISPR array. the CRISPR array has been expanded (new info, new spacer, ner repeat) and is transcribed. Cas proteins are formed and crispr RNA matures as Cas6/E cuts the loops of repeats (of pre crRNA). crRNA is loaded into the cascade proteins (Cas9)
when a known phage enters the cascade recognises the viral DNA (complementary sequence to the crRNA inside) and recruits the Cas 3 nucelease-helicase to cut the viral DNA
what is the Protospacer Adjacent Motif
A protospacer adjacent motif (PAM) is a 2–6-base pair DNA sequence immediately following the DNA sequence targeted by the Cas9 nuclease in the CRISPR bacterial adaptive immune system.
where does crispr first bind to the viral RNA
at the seed (5 nucelotides next to the PAM) in the protospacer
what are the 3 steps of invader DNA recognition in CRISPR-Cas
finds PAM sequence then scans for complementary protospacer . when it finds the correct complementary match it starts forming an R loop which recruits Cas3 to cleave one side of the loop
what are the 3 major stages of CRISPR-Cas immunity
adaptation
expression
interference
how does the invading virus escape the CRISPR immune system
- mutations in the seed of the phage (so crRNA doesnt recognise it)
- anti-CRISPR proteins
