Camerini 3 - Lecture 3 tRNA mRNA and Ribosomes Today we...

Info icon This preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Lecture 3: tRNA, mRNA and Ribosomes Today, we will discuss the following: The structure of tRNA The “adaptor hypothesis” and the “second genetic code” tRNA synthetases and tRNA synthesis reactions; double sieve model The “wobble” hypothesis mRNA structure; signals that regulate protein synthesis Ribosomes and protein synthesis; polysomes Composition of ribosomes Ribosome structure
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
2 tRNA functional sites A-form double helix
Image of page 2
3 Tertiary Structure of tRNA Acceptor (AA added here) D-loop folds over to contact the TyC loop Anticodon
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
4 “Adaptor hypothesis” Raney Nickel experiment Crick (1958): soluble RNA (sRNA) acts as adaptor for incorporation of AAs into proteins. Günther Von Ehrenstein (1961): chemically modified an AA attached to tRNA; (Cys to Ala, Raney Nickel expt.) Result: Ala inserted at site of Cys! Demonstrates that specificity is dictated by the “adaptor” not by the protein synthesis machinery (e.g. ribosome)
Image of page 4
5 tRNA Synthetases Class I tRNA synthetase 3D structure, glutaminyl-tRNA synthetase (blue; tRNA in red & yellow) 20 different synthetases, one for each AA Two classes: type I and type II Type I: transfer AA to 2’ OH of Adenine at end of acceptor stem (CCA); requires trans-esterification to transfer AA from 2’ to 3’ OH of tRNA. Bind minor-groove of acceptor stem. , both 2 domain structures Type II: transfer AA to 3’ OH of Adenine. Bind to major groove of acceptor stem. Both classes have 2 domains: -catalytic domain (interacts with 3’ CCA) -variable domain: binds to tRNA recognition domain tRNAs also have 2 functional domains: -anticodon -CCA acceptor (3’)
Image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
6 tRNA synthesis reactions Two types of tRNA synthetases: Class I: usually monomeric; AA added to 2’ OH of A Class II: oligomeric; AA added to 3’ OH Two phases of reaction catalyzed by tRNA synthetase: Type II Type I
Image of page 6
7 Aminoacyl-tRNA synthetases: the “second genetic code” Note that Ile and Val have similar size and charge. The specificity of first reaction not absolute; Ile-tRNA synthetase will catalyze transfer of adenine (from ATP) to valine. Prior to 2nd step (transfer of valyl-adenylate to acceptor of Ile-tRNA), Valine will trigger deacylase site of Ile- tRNA synthetase , which hydrolyzes the aminoacyl- adenylate. As described earlier, ribosomes don’t provide the specificity, the aminoacyl-tRNA synthetases do. How?
Image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
8 Specificity of tRNA charging: the “double sieve” model Two ways for tRNA synthetase to “know” if the wrong AA is bound (prior to charging): 1. If AA is too large, it cannot enter.
Image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern