CRISPR-Cas Flashcards

1
Q

uses

A

to find what species are present in the gut

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2
Q

defense system

A

This defense system resides in half of the bacterial and almost all the archaeal genomes currently sequenced.
The immune system is characterized by its Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) and the CRISPR-associated (cas) genes

The CRISPR-Cas system relies on small non-coding RNAs to track and inactivate invasive genetic elements (e.g. conjugative plasmids or phages), to protect the cell’s genomic integrity.

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3
Q

why is it different to innate resistance mechanisms

A

In contrast to innate resistance mechanisms, the CRISPR-Cas system is unique in that it is invader-specific, adaptive and heritable. This means that the immune system has a memory that can be altered and passed on to its progeny.

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4
Q

composition

A

CRISPR loci (CRISPR arrays including the leader sequence and the associated cas genes) are found solely in organisms from the archaeal and bacterial domains of life. CRISPR loci exhibit several universal features:

(i) multiple direct repeats with identical or nearly identical, often palindromic sequences (black diamonds),

(ii) non-repetitive similar-sized spacer sequences (numbered rectangles),

(iii) a leader sequence flanking the repeats at one end (between cas2 and de first repeat),

(iv) and the genetic association of the direct repeats with cas genes (for example cas1).

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5
Q

repeats

A

The direct repeats are 28-40 base pairs in length and their number per CRISPR array can vary dramatically from one organism to another.

On average, an archaeal genome contains approximately five CRISPR arrays, while three CRISPR arrays are found per bacterial genome

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6
Q

spacer sequence

A

The spacer sequences are highly variable constituents of the CRISPR arrays ranging from 26 to 72 bp in length

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7
Q

leader sequence

A

This sequence is located at the 5’-end of the CRISPR array and is abundant in adenine and thymine nucleotides. Leader sequences have been shown to drive transcription of the CRISPR array, but may also be involved in the integration of new spacer sequences at the leader end of the CRISPR array.

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8
Q

mechanism

A

(1) CRISPR adaptation (Fig. 2, step 1-3); during this stage new spacers are added to the existing CRISPR array.

(2) CRISPR expression an crRNA maturation (Fig. 2, step 4-5); the array is transcribed into a long pre-crRNA transcript and processed to yield small crRNAs. These mature crRNAs, with the size of a single spacer and repeat, are retained by a complex of Cas proteins.

(3) CRISPR interference (Fig. 2, step 6-8); when infection takes place by a virus that is archived in the CRISPR blacklist, the crRNA-loaded protein complex uses the crRNA as a guide to recognize the invading DNA. The elimination of the viral DNA is carried out by the Cas protein complex alone or together with additional Cas proteins.

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