320Fall09Homework5_key - Cell Biology (BIO 320), Fall 2009,...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Cell Biology (BIO 320), Fall 2009, Dr. Bushart Homework set #5 1. Why is it crucial that the signal peptide is removed after translocation of a soluble lumen protein of the ER? The signal peptide is a hydrophobic region that remains inserted in the membrane through laterally gating of the translocator (Sec61). If it is not removed then the protein as a whole remains bound to the membrane by its signal sequence and cannot be freely soluble. 2. A particular ER protein contains an internal non-cleavable ER signal sequence. This sequence is flanked by positive charges towards the N-terminus and negative charges on the C-terminal side. There are 4 other regions of significant positive value on a hydropathy plot. a. Give a rough sketch of the protein based on its description. Be sure to appropriately label the ends of the protein as C and N. This protein will be a transmembrane protein embedded in the ER. Based on the charges around the signal sequence the N-terminus will be in the cytosol (the picture should have the sides of the membrane labeled as well). The 4 hydrophobic regions (based on the hydropathy) will be transmembrane passes. The peptide chain therefore crosses the membrane a total of 5 times. This puts the C-terminus in the lumen of the ER. b. Is the last hydrophobic region acting as a start or stop transfer? How do you know (or is it not possible to determine?)? The last region is a start transfer. We can know this because it is only the order of regions that matters. The initial orientation of the signal peptide establishes it as a normal start transfer [unlike the figure in the book]. The new part of the polypeptide
Background image of page 1

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

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/25/2010 for the course BIO 51055 taught by Professor Bushart during the Fall '09 term at University of Texas at Austin.

Page1 / 2

320Fall09Homework5_key - Cell Biology (BIO 320), Fall 2009,...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online