Hello guys, Welcome to Africa's Largest Video Search Engine, and you are watching Nonsense-Mediated Decay (NMD), NonStop Decay, & No Go Decay (mRNA surveillance pathways). and this video is uploaded by the bumbling biochemist at 2023-02-20T11:13:56-08:00. We are just promoting this video only for entertainment and educational purpose only. I hop you like our Video Search Engine. [Z6_ny9DE9Yw]
| Name | Nonsense-Mediated Decay (NMD), NonStop Decay, & No Go Decay (mRNA surveillance pathways) |
| Video Uploader | Video From the bumbling biochemist |
| Upload Date | This Video Uploaded At 20-02-2023 19:13:56 |
| Video Discription | In each of your billions of cells, millions of ribosomes are traveling along hundreds of thousands of messenger RNAs (mRNAs), using the mRNA’s instructions to piece together the correct amino acids to form desired proteins (in a process called translation). Perhaps even more amazing is that all goes well most of the time - but not always! If there is a problem with the mRNA, the ribosome can get stuck (stall) when trying to translate it. This stalling is actually a good thing, though, because it alerts to cells that something’s wrong with the mRNA, and allows them to come in with their destruction machinery to degrade the faulty mRNA before other ribosomes reach the same fate and before more messed-up proteins or partial proteins get made. blog form: https://bit.ly/translation_coupled_mRNA_decay There are 3 main forms of mRNA surveillance that take place, which differ in what kinds of faulty mRNA they detect and what molecular machinery is involved. These 3 pathways are: * Nonsense Mediated Decay (NMD) - deals with mRNA transcripts that have premature stop/termination codons (PTCs) so the ribosome stops making a protein midway through * NonStop Decay (NSD) - deals with the sort of opposite situation, transcripts that are missing stop codons, so the ribosome plows on through to the end end of the transcript, polyA tail and all, and still can’t recruit the termination machinery needed to let it off * NoGo Decay (NGD) - deals with ribosomes that stall for some other reason (weird secondary structure, etc.) and cause traffic jams (ribosome collisions) They may use different players but the end result is usually the same: * Degrade the mRNA so other ribosomes don’t try to use it: cut the mRNA near the stalled ribosome, exposing unprotected ends to RNA chewers (exonucleases) that can finish the job * Degrade the nascent (newly-formed) peptide (the probably messed-up protein that was getting made) before it can go around wrecking havoc in the cell: ubiquitinate it (attach a little protein called ubiquitin to it) to give it a ticket to the protein shredder (proteasome) * Free the ribosome - it wasn’t its fault and a lot of work and energy, lots of protein and RNA parts, went into making it so you want to use it as much as possible!: proteins called helicases spend energy to kinda pry things apart * Check the tRNA and reuse if all’s okay: the tRNA gets cut in the ribosome associated quality control pathway (RQC) and the cut leaves a characteristic signature that allows it to be flagged for a check-up and repair before being released into circulation The terminology gets kinda muddled and aspects of the specific pathways overlap, but NSD and NGD have more in common with each other than with NMD. And from my best understanding, these two are said to follow a ribosome associated quality control pathway (RQC). In these pathways, stalled ribosomes are detected (such as by sensing collisions) and tagged by ubiquitin. Instead of targeting them to the proteasome like ubiquitin often does, these ubiquitination makes them the target of proteins that will split the ribosome into its large and small subunits. It’s kinda like prying open a jammed stapler - opening it up makes it easier to get out the peptide - and it provides access to sites for a different ubiquitin ligase (called Listerin) to come in and ubiquitinate that chain. Although Listerin binds at the base of the large subunit, it wraps around to the top, kinda like the handle of a coffee mug, and does the actual ubiquitination up top, where the chain’s exited the tunnel already. It can’t ubiquitinate just any old place on that chain however. It needs there to be a readily-accessible lysine (one of the amino acids). If there’s not a lysine that fits the bill, the cell tries to make one. In a process called CAT tailing (seriously!), a complex adds a Carboxy Terminal tail to the growing end of the peptide. This tail consists of untemplated adenines and threonines (other amino acids). Adding them to the growing end pushes the amino acids hidden in the peptide exit tunnel out of the tunnel. If there was a lysine, now that lysine can be seen! In the case of NonStop Decay, if the ribosome has traveled into the polyA tail it will start putting in lysines because AAA codes for lysine (when the ribosome encounters AAA it incorporates a lysine into the growing chain). So lysine shouldn’t be a problem (but the messed up transcript is!) finished in comments [Z6_ny9DE9Yw] |
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