Exam_3__Fall_07__KEY - Penn State Forensics NAME: KEY BMB...

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Penn State Forensics Science Serving Justice NAME: KEY BMB 400 EXAM 3 14 November 2007 100 POINTS 1. With the help of the spliceosome figure provided below, list the steps involved in the splicing of exons in the order in which they occur . (Hint: there are ~6 steps) Make sure to account for all contributing factors/snRNPs. How are the initial splicing factors recruited to the individual splice sites? 10 Points 1. The snRNP U1 binds to the 5’ splice site and the protein factor BBP (B ranch-point B inding P rotein) binds to the branch site, with the help of respectively ) 2. The snRNP U2 binds to the branch point and displaces BBP, again with the help of the U2AF’s, causing the branch point A to protrude 3. The snRNP complex U4U5U6 binds and U1 is displaced by U6 4. U4 is displaced through interactions between U6 and U2, producing the “active site” 5. The formation of the active site brings the 5’-splice site and the branch point together and facilitates the first transesterification reaction 6. The U5 snRNP subsequently uses protein:protein interactions to bring the 3’-end of the 5’-exon into proximity with the 5’-end of the 3’-exon and facilitates the second transesterification reaction The splicing factors are delivered by the phosphorylated CTD tail of the RNAP II. SR (serine/arginine) rich protein factors bind to ESE (exonic splicing enhancer) sites and help to recruit the initial splicing machinery (U2AFs and U1).
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Page 2 BMB 400 Exam 3 14 November 2007 Initials _____________ 2. Is the DNA sequence shown below involved in Rho-dependent or Rho- independent termination of transcription, and why ? 5 Points Rho-independent The inverted tandem repeat (shaded in blue), once transcribed, will form a hairpin loop which will temporarily block the exit channel of RNAP II. The stretch of U’s in the transcript (downstream of the hairpin), will weaken the association of the transcript with the template and, along with the hairpin providing a temporary block in the exit channel, will facilitate release of the transcript and termination of transcription. 3. What are two ways that an aminoacyl-tRNA synthetase ensures that the correct amino acid is added to the correct tRNA. 4 Points 1. The initial recognition mechanism of the synthetase (i.e., which amino acid is being added to the tRNA), and the editing domain in the enzyme that recognizes and removes the wrong amino acid attached to the 3’-end of the tRNA 2. The acceptor stem (including discriminator base) and anticodon region of the tRNA have affinities for the correct synthetase
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Page 3 BMB 400 Exam 3 14 November 2007 Initials _____________ 4. List three of the four primary roles for the (sigma) factor subunits in transcription initiation. 6 Points
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This note was uploaded on 03/31/2008 for the course B M B 400 taught by Professor Holland,mitchell during the Fall '07 term at Pennsylvania State University, University Park.

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Exam_3__Fall_07__KEY - Penn State Forensics NAME: KEY BMB...

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