CBIO 3400 Lecture Notes - Lecture 4: Crispr, Cas9, Base Pair
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Exam 4 Lecture 4
Genome Editing and CRISPR/Cas9
Bacterial Adaptive Immune System: CRISPR-Cas9 Invader Immunity
• CRISPR: Clustered Regularly Interspace Short Palindromic Repeat
• It’s a type of bacterial adaptive immune strategy.
• Certain regions in the genome that look strange → Short palindromic sequences (repeat
regions scattered throughout the genome)
o This is how they protect themselves from invading pathogens they have to deal
• CRISPR locus
o Repeat regions- Short palindromic sequences
▪ Reads the same forward as it does backwards.
▪ Palindromes (CGTT, GCAA), these things base pair with each other and
create hair pin structures which is important of the processing of CRISPR
▪ Hair pin helps tell us where we want to cut the sequence
▪ Palindromes help id the target regions for bacterial phages. Serve as book
ends to help separate the functional pieces
o In b/w repeat regions, there are spacers.
▪ The different “spacer” regions correspond to foreign DNA elements
o Cas genes- Cas = CRISPR-Associated genes
Overview of the CRISPR-Cas9 Pathways
• Bacteria phage inserts its genome into the bacteria.
• Adjacent to PAM (protospacer adjacent motif)
o NGG is the PAM sequence for CRISPR-Cas9 nuclear machinery
o PAM are everywhere.
• Cut out spacer region and put it in-between the repeated sequences
• Transcribes RNA from this locus
o Makes CRISPR RNA which fit into the Cas machinery
• Makes a cut in double stranded DNA
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