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Title: GTP hydrolysis in mRNA translation Post by: i_love_science on Dec 1, 2023 How many GTP are necessary to synthesize 2 linear peptides of 11 amino acids each using an in vitro prokaryotic system? Assume the tRNAs provided are already loaded with their proper amino acids. All 3 steps of the protein synthesis reaction must be completed.
My answer was 46. I thought that translation initiation uses 2 GTPs (the GTPs on IF2 and IF5B are hydrolyzed). Elongation involves 2 GTPs for each amino acid after the first methionine (the GTPs on EF1𝛂 and EF2 are hydrolyzed) - there are 10 amino acids left, so 2x10=20 GTPs are used. Termination involves 1 GTP (the GTP on RF3 is hydrolyzed). So for one linear chain of 11 amino acids, 2+20+1=23 GTPs are used, and for 2 chains, 46 GTPs are used. The correct answer is 44. I'm not sure where in my reasoning I went wrong. In what steps were there less GTPs used, and which proteins instead did not actually have GTP hydrolysis? Thank you. Title: Re: GTP hydrolysis in mRNA translation Post by: bio_man on Dec 1, 2023 Termination involves 1 GTP (the GTP on RF3 is hydrolyzed). I believe the mistake is here. Do you have a source that can confirm a GTP is required for the stop codon? Title: Re: GTP hydrolysis in mRNA translation Post by: caitlynhartzog on Dec 1, 2023 Where are you getting information on GTP required for the process? I've been browsing a whole bunch of images on the translation, and all of them don't seem to include GTP as an energy source.
Title: Re: GTP hydrolysis in mRNA translation Post by: bio_man on Dec 3, 2023 Excerpt The ribosome has three tRNA-binding sites, designated P (peptidyl), A (aminoacyl), and E (exit). The initiating N-formylmethionyl tRNA is positioned in the P site, leaving an empty A site. The second aminoacyl tRNA (e.g., alanyl tRNA) is then brought to the A site by EF-Tu (complexed with GTP). Following GTP hydrolysis, EF-Tu (complexed with GDP) leaves the ribosome, with alanyl tRNA inserted into the A site. A peptide bond is then formed, resulting in the transfer of methionine to the aminoacyl tRNA at the A site. The ribosome then moves three nucleotides along the mRNA. This movement translocates the peptidyl (Met-Ala) tRNA to the P site and the uncharged tRNA to the E site, leaving an empty A site ready for addition of the next amino acid. Translocation is mediated by EF-G, coupled to GTP hydrolysis. The process, illustrated here for prokaryotic cells, is very similar in eukaryotes. (Table 7.1 gives the names of the eukaryotic elongation factors.) 2 GTP per amino acid and two polypeptide 11 * 2 * 2 = 44 Title: Re: GTP hydrolysis in mRNA translation Post by: i_love_science on Dec 8, 2023 Termination involves 1 GTP (the GTP on RF3 is hydrolyzed). I believe the mistake is here. Do you have a source that can confirm a GTP is required for the stop codon? My textbook says that in termination, release factor 3 (RF3)•GTP is hydrolyzed to RF3•GDP, allowing the peptide chain to be cleaved and the tRNA and polypeptide chain to be ejected. Title: Re: GTP hydrolysis in mRNA translation Post by: bio_man on Dec 9, 2023 Thanks for the source ^^
https://www.ncbi.nlm.nih.gov/books/NBK9849/ I didn't realize the amount of detail this process is described in - we've certainly come a long way since I graduated. However, i_love_biology (https://biology-forums.com/index.php?action=profile;u=901658) should keep in mind that if his text is geared towards a more advanced audience, then perhaps the questions you're studying expect a less detailed approach to answering them. In other words, your reasoning may be correct, but the reasoning they are seeking is simpler, like that mentioned by the anonymous poster. Quote 2 GTP per amino acid and two polypeptide 11 * 2 * 2 = 44 |