Term
| What are ribonucleoproteins (RNPs) |
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Definition
| RNAs and proteins that play a large role in splicing |
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Term
| What are heterogenous nuclear RNAs? |
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Definition
| Longer than mRNAs, 5'cap and polyA tail, short lived, that never seem to be mentioned again |
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Term
| What is the spliceosome composed of? |
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Definition
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Term
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Definition
| A specfic adenin in the intron attacks the 5' splice site, cutting the sugar phosphate backbone. The 5' inton then links to the adenine nucleotide that attacked the splice site, the 3' end reacts with the next exon, and the intron is released as a lariat? |
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Term
| What happens to lariats after they are released? |
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Definition
| Most are digested and recycled, but some are repurposed into snoRNAs etc. |
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Term
| What are the two types of spliceosome? |
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Definition
U2 - regular
U12 - rare, only in certain eukaryotes |
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Term
| How is the spliceosome assembled? |
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Definition
| The U1 snRNA binds to the pre-mRNA, followed by U2. This is now the pre-spliceosome complex, or A complex. U4/6 and U5 also bind to form the pre-catalytic spliceosome complex. Major rearrangments in RNA-RNA and RNA-protein interactions then lead to the destabilization of U1 and U4, leading them to dissociate and the activated spliceosome is formed, also known as the Bact complex. This is activated by RNA helicase Prp2, and ATP, which generates the B* complex, and this catalyzes the first two steps of splicing. This leads to the formation of complex C, which catalyzes the last step, after which the spliceosome dissociates and is remodelled. |
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Term
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Definition
| Exactly what it sounds like. An exon is skipped. |
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Term
| What is cryptic splice site selection? |
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Definition
| A cryptic splice site is used instead of the needed one, leading to only a portion of an exon being included |
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Term
| How is splicing altered in alternative splicing? |
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Definition
Transcription elongation rates - affect excision of introons
Secondary structure of pre-mRNA can alter spliceosome access
Protein bind to pre-mRNA and enhance/repress spliceosome assembly |
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Term
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Definition
| A drosophila cell adhesion molecule required for formation of neuronal circuits. 20 constitutively spliced exons, 95 alternatively spliced - arranged into 4 blocks. Many different potential isoforms. Offers increased binding specificity with few amino acids having large differences in binding affinities. |
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Term
| What 3 steps need to have occured before nuclear export can? |
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Definition
Capping
Splicing
3'end formation |
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Term
| What are the main structural elements of the nuclear pore? |
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Definition
| nuclear basket, connected to the ring subunit via nuclear fibrils, annular subunits inside the pore, cytosolic fibrils extending into the cytosol, and nucleoporins (Nups) - standard name fro proteins that compose the nuclear pore complex |
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Term
| How does nuclear export occur? |
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Definition
| First, TAP is recruited to the mRNA, before attracting multiple other proteins such as EJC, NXF!, ALY and p15. Next, the mRNA is localised to the NPC periphery, which pulls it toward the basket for docking. Proteins then allow the translocation along the fibrils untils it is in the basket ready for cytoplasmic release. |
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Term
| What occurs after nuclear export? |
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Definition
| The translocation proteins are released, and the cap modified. When it leaves the NPC it is bound by intiation factors for protein synthesis. It then goes through nonsense mediated decay to lose the capping binding protein. The mRNA is now ready for translation. |
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Term
| What are the two main methods foreign objects can use to move through the nuclear envelope? |
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Definition
| NPC enlargement and nuclear envelope budding. |
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Term
| How does translation occur? |
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Definition
The mRNA enters in the A site, and the charged tRNA binds to the transcript in the A site and brings with it the next amino acid for the chain.
The tRNA moves to the P site, where it is able to bind the amino acid to the chain. The next charged tRNA binds to the A site with the required amino acid based on the codon.
The original tRNA moves to the E site (and exits), the second tRNA can move to the P site and bind the aa to the end of the chain, and the A site is free for the next tRNA. (start cycle again). |
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Term
| How does Cap mediated initiation occur? |
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Definition
It begins with a methionine, which can recognize the AUG codon.
Initiation factors specially identify this tRNA, which is loaded into the small ribosomal subunit along with eIFs (eukaryotic initiation factors).
Small ribosomal subunit binds to the 5’ end of mRNA, by virtue of its cap and moves forward (5’ to 3’) in search of AUG codon.
At this point initiation factors dissociate, allowing the large ribosomal subunit to assemble with the complex |
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