Lecture 12. Bacterial Genetics III.docx

Describe the part of a bacterial crispr locus short

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Describe the part of a bacterial CRISPR locus: short direct repeats, spacers, CRISPR-associated genes (cas). For a visual aid look at figure 9.12 (anatomy of CRISPR locus). Note that there are different kinds of cas genes, core or subtype-specific. There are other sequences like RAMP which seem to encode a polymerase, don’t worry too much about those. Focus on repeats, spacers and cas. Which of these sequences are coding vs. non-coding? Cas vs. spacer and repeat\ What i is the role of CRISPR in bacterial immunity to phages? (CRISPR function). Be able to explain how the locus works, producing crRNAs, and how the complex cas-crRNA target the phage’s DNA. Use figure 9.13 as visual aid (An overall model of CRISPR/Cas activity) CRISPR locus acquire spacers by incorporating a piece of an invader’s DNA. One or more CRISPR Cas proteins may cleave part of the phage genome and integrate it as the lead spacer. Locus is transcribed upstream. RNA transcript is cleaved and trimmed into small RNAS composed of a single spacer sequence (crRNA- aka guide RNA). Each crRNA associates with Cas to form a riboprotein complex that binds to a homologous sequence from an infecting phage/plasmid and directs cleavage of foreign DNA-> infect cell is spared destruction. Skip section 9.2 (recombination) Section 9.3 Mutations: define and be able to explain the following mutations: spontaneous, induced, transition, transversion, point mutation, insertion/deletion, inversion, reversion, silent, missense, nonsense, frameshift, loss-of-function, gain-of-function, knock out.
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Can mutations arise spontaneously inside cells?
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