Lecture 11

Lecture 11 - Lecture 11: Conformational changes: IF-2,...

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Lecture 11: - Conformational changes: IF-2, EF-Tu and EF-G are all examples of G proteins that undergo large conformational changes upon GTP hydrolysis o Movement of helix: form a big hole in the center of the molecule o EF-Tu, when bound to GDP (after hydrolysis), the molecule changes conformation – it gets stretched out – the subunits are stretched further away from each other = release of tRNA o When EF-Tu binds to GTP, the subunits are pretty close to each other So G proteins are kind of like a “switch” – because hydrolysis causes the large conformational change (that’s what the energy is being used for ) Wobble is different from this – Wobble is correct base pairing This conformational change is what’s driving translocation – release of tRNA, etc All of the tRNAs come into attached and this change in conformation is what releases it o EF-Tu brings in the charged tRNA to the A – Site The binding of tRNA occurs in the center/middle hole of the molecule If there is not a match between the codon and the anticodon, they (tRNA) come back out, they don’t release it If there is a match, that’s what stimulates GTP hydrolysis There is the movement and release of tRNA The tRNA moves into the A-site and is ready for peptide bond formation o We are using a lot more GTP than ATP when we synthesize proteins and it’s all the regulate these different processes and cause movement or translocation of the ribosome - Sum m ary of Elongation: o Binding a a-tRNA (amino acyl tRNA) with assistance by EF-Tu-GTP GTP hydrolysis The EF-TS: elongation factor that is involved in regen erating EF- Tu back into the GTP state (we won’t worry too m uch about that
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o Peptide bond formation: Nitrogen (N) on incoming aa-tRNA (amino acyl tRNA) attacks  carbonyl on peptide-tRNA (carbonyl that’s attached between the  peptide and the t-RNA), catalyzed by 23S rRNA Basically at the attack on carbonyl peptide-tRNA, you release  the tRNA and transfer this peptide to the new t-RNA This was initially thought to be catalyzed by 23S rRNA (we  know know that it’s more catalyzed by the 2’ hydroxyl) o Translocation  tRNA in P site moves to E site (peptide no longer attached –  moves to the Exit Site)), tRNA in A site moves to P site (tRNA in  the A site now has the peptide on it so it moves to the A-Site) The process and movements of tRNA from each site is facilitated  by EF-G-GTP (a G protein: EF-G), and hydrolysis of GTP (we  hydrolyze another GTP in the process) Addition of every aa uses 2GTPs and 1ATP ATP is the charging of the amino acyl-tRNA So for every peptide bond, we hydrolyze three high energy  bonds (this is a very high energy process to synthesize proteins) Termination of Proteins Synthesis: - Stop codon is recognized by release factors
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Lecture 11 - Lecture 11: Conformational changes: IF-2,...

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