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13 Cards in this Set
- Front
- Back
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what happens when iron is low in the cell? high? (when is mRNA stable/unstable) |
iron low -> aconitase binds 3'UTR IRE (iron response element) and inhibits adjacent destabilizing sequences -> mRNA stable iron high-> aconitase binds iron and aconitase releases from 3' UTR IREs-> transferin receptor mRNA unstable |
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during high iron levels, what happens to IRE-stem-loops? |
unprotected IRE stem-loops susceptible to attack by RNase, which clips mRNA & exposes its 3' end for degredation |
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what are siRNA? cis or trans? |
short interfering RNA are produced artificially or in vivo from dsRNA precursors (trans acting: ie, external to the cell) trans acting |
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what are miRNA? cis or trans? |
microRNA derived from precursor RNAs that are encoded by genes expressed in cells where those miRNAs have specific regulatory functions (cis acting) |
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what are piRNAs? |
piwi-interaction RNAs, expressed predominantly in the germline and have features distinct from miRNAs |
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how are siRNAs and miRNAs made and the mode of action? |
Dicer processes dsRNA and pre-miRNA to make siRNAs and miRNAs The siRNAs and miRNAs direct a complexcalled RISC (RNA-induced silencing complex)to repress gene expression in three ways It attacks and digests mRNA that hashomology to siRNA and/or miRNA It interferes with translation of those mRNAs It directs chromatin-modifying enzymesto the promoters that direct expression ofthose mRNA 8 |
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how are siRNAs amplified? |
by RdRP, siRNA+RISC complex recruits RdRP to the targeted RNA where it uses siRNA as a primer to create dsRNA, then dicer cleaves and thus amplifying siRNA |
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compare and contrast siRNAs and miRNAS
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siRNA reduces target mRNA expression by transcript degredation, miRNAs can also but without degredation siRNAs transfect forgein pieces of RNA (trans) miRNAs normal and naturally occuring (cis) siRNAs made to bp perfectly with target RNA (anywhere on the length) miRNAs can imperfectly bp (usually 3') |
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how are miRNAs made? |
produced by 2 cleavage events by RNASE III-like enzymes (Drosha and Dicer) first drosha cleavage to get pre-miRNA, then dicer cleavage for dsRNA, then miRNA binds and guides argonaute protein to target mRNA |
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what is drosha and dicer? |
drosha - nuclear cleavage dicer - cytoplasmic cleavage |
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what kind of structure does Argonaute have? |
RNA-binding regions and RNAse H-like nuclease domains |
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what happens in perfect pairing between miRNA and target 3' UTR and in imperfect pairing? |
imperfect pairing -> translational block (no transcript degradation) perfect pairing -> mRNA cleavage and degredation |
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explain how phage T7 RNAP is used in manipulating gene expression |
used in RNAi (RNA interference)
the gene for the T7 RNAPis expressed artificially in these cells,under control of the lac promoter. |
