Term
| How does RNA stability flucuate and what are some contributing factors to this stability? |
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Definition
mRNAs vary greatly in stability. The balance between mRNA degradation and transcription of new messages determines the level of individual mRNA in cell. The 5' caps and 3' tails contribute to mRNA stability and sequence elements present in some mRNAs cause them to be less stable. Quickly degraded mRNAs usually have A-U rich sequences in the 3' UTR |
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Term
| How does nonsense-mediated mRNA decay work? |
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Definition
(see slide 4) A splicing mistake leaves an intron and this particular intron contains a stop codon. Surveillance proteins detect the splice junction binding proteins since the ribosome stalls at a premature stop codon. The RNA is then decapped and degraded by nucleases |
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Term
| How do silk worms produce so much fibroin (the main component of silk)? |
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Definition
Their silk glands first become highly polyploid so they accumulate thousands of copies of each chromosome. 2. The fibroin gene has a very strong promoter which results in about 10,000 mRNA messages per copy of DNA. 3. The fibroin mRNA lasts for days instead of 3 hours like most mRNA |
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Term
| Is encoding proteins the only function that RNAs have? |
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Definition
No. tRNAs are involved in transfer RNA translation, snRNPs are involved in splicing and miRNAs/RNAi's are involved in the regulation of gene expression |
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Term
| How do small regulatory RNAs control translation? |
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Definition
They base-pair with mRNA transcripts. This involves anti-sense RNA pairing with mRNA transcript in order to be regulated and these srRNAs can activate or inhibit RNA translation. Anti-sense mediated silencing lead to the discovery of RNAi (RNA-interference) |
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Term
| What is the interaction between regulatory OxyS RNA and flhA mRNA? |
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Definition
OxyS keeps flhA turned off in times of stress. Complimentary loops can undergo base pairing which inhibits the ribosomal binding site and inhibits translation |
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Term
| How does the regulatory RNA DsrA affect rpoS mRNA? |
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Definition
DsrA turns on rpoS. The ribosome-binding site is hidden in the stem of the stem and loop structure in the rpoS RNA and base pairing between the sections opens up the ribosome binding site |
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Term
| What is RNAi and how does it work? |
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Definition
RNAi is RNA interference which uses a double-stranded RNA (dsRNA) to target and destroy matching RNA (this silences gene expression). Destruction of mRNA is accomplished by the protein/RNA complex called RNA induced silencing complex (RISC) |
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Term
| How can RNAi be used experimentally and what else can be used for this process? |
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Definition
RNAi is a valuable experimental tool for investigating gene function in many organisms. Similar small RNAs called microRNAs (miRNAs) are important regulators f gene expression |
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Term
| What was the initial theory regarding dsRNA before Mello and Fire's experiment? |
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Definition
The theory was that dsRNA couldn't be translated |
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Term
| What was the theory after Mello and Fire's 1998 experiment regarding dsRNA? |
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Definition
They showed that dsRNA had been a contaminant in their initial trials. They realized that inorder to properly analyze the results of the normal and twitchy phenotypes they had to first purify the ssRNA from the ss+ds samples |
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Term
| How do cells use RNAi for their own good? |
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Definition
Cells can use RNAi to fight viruses. RNAi machinery can detect viruses with dsRNA genomes, viral RNAs that form hairpins, viral RNAs that form dsRNA due to bidirectional transcription |
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Term
| How do viruses "fight back" when cells use RNAi mechanisms to try and fight them off? |
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Definition
A dicer cleaves the dsRNA and leaves a dsRNA duplex. The virus then produces a protein called p19 which sticks to the dsRNA and keeps RNAi from targeting viral genes |
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Term
| How could some potential RNAi-based therapies work? |
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Definition
They work by knocking down gene expression so the trick is the find diseases where over-expression is a problem. The challenge, however, is delivery that is targeted, not transient and doesn't set off the immune system |
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Term
| What are small RNAs also known as and why are they so interesting? |
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Definition
Small RNAs are also called micro RNAs (miRNAs). They are interesting because they are good research tools, they're potentially therapeutic, they're found in diverse organisms and they might regulate as many as 30% of vertebrate genes |
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Term
| How do miRNAs regulate gene expression? |
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Definition
They usually regulate gene expression by blocking translation |
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