F08 LS1a Pset 4keyfinalst-1

F08 LS1a Pset 4keyfinalst-1 - Name: TF Name: LS1a Fall 08...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Name: TF Name: 1 LS1a Fall 08 Problem Set #4 Due Monday 10/27 at noon in your TF’s drop box on the 2 nd floor of the Science Center 1. (28 points) Porins are transmembrane proteins with hollow centers through which small molecules can diffuse. The structure of one is shown below (in sideview). (a) What is the predominant secondary structure feature in a porin? (4 points) beta sheets (b) This particular porin allows the passage of sucrose into the cell. When the sequence of a single yellow protein strand is analyzed, it is discovered that consecutive amino acids alternate between hydrophobic and hydrophilic residues. Does this make sense? Briefly explain. (8 points) Yes, the side chains in a beta sheet alternate between above the plane of the sheet and below the plane of the sheet. For porin the hydrophobic side chains are in contact with the hydrophobic fatty acid tails of the membrane phospholipids and the hydrophilic side chains point into the aqueous environment of the channel.
Background image of page 1

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

View Full DocumentRight Arrow Icon
Name: TF Name: 2 (c) If this porin protein is tagged with a fluorescent molecule and FRAP is performed, the results below on the left are seen. If another transmembrane protein (Protein A) is tagged with a fluorescent molecule and FRAP is performed, the results below on the right are seen. Which of these proteins is more mobile in the plasma membrane? Briefly explain. (8 points) Protein A is more mobile. The fluorescence in the bleached area of the membrane for Protein A recovers fairly quickly whereas there is virtually no recovery of fluorescence in the bleached area of the membrane where porin is labeled. (d) Brief treatment with proteases cleaves some peptide bonds that are on the surface of a protein and more accessible. If the membranes containing either tagged Porin or tagged Protein A are briefly treated with a protease and then FRAP is preformed, the mobility of both proteins are indistinguishable from the results shown above for Protein A. Based on this information, provide a plausible explanation for the mobility of Porin in the absence and presence of protease treatment. (8 points) Porin is anchored to another protein restricting its mobility in the membrane. When the membranes are treated with protease, it breaks the association between porin and the fixed protein and allows protein to be mobile in the membrane.
Background image of page 2
Name: TF Name: 3 2. (32 points) A new method of DNA sequencing involves passing a single strand of DNA through a protein pore in a membrane. As each individual monomer subunit
Background image of page 3

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

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 03/23/2011.

Page1 / 7

F08 LS1a Pset 4keyfinalst-1 - Name: TF Name: LS1a Fall 08...

This preview shows document pages 1 - 4. Sign up to view the full document.

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