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MBB 222 Study Guide - Midterm Guide: Membrane Transport Protein, Disulfide, Beta Turn

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browncricket987
20 Dec 2018
School
Simon Fraser University
Department
Molec Biol & Biochem
Course
MBB 222
Professor
Adam Barlev

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Document Summary

Porins are passive membrane transport proteins consisting of -barrel structures that provide a channel for ions and small molecules to pass through the outer membrane of gram- negative bacteria. Porin - a passive membrane transport protein that has a -barrel structural motif and is abundant in the outer membrane of bacteria, mitochondria, and chloroplasts. Alpha helix: backbone on inner portion of helix, side chains on outer portion // right vs left handed. Beta sheet: polypeptides are linear, stacked on top of one another // parallel vs antiparallel. Parallel: an amino acid on one strand interacts w/ 2 amino acids on opposite strand. Beta turn: c=o group of nth amino acid interacts with h-n group of n+3 amino acid (hydrogen bond). R groups on beta turns interact with polar solvent found outside proteins (hydrophilic). Understand the molecular interactions that stabilize a folded protein.

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Related Questions

The non-polar core of a membrane bilayer is found to be 3.4 nmin thickness. From studies of protein structure, we know that eachamino acid residue in a beta strand extends the length of thestrand by 0.35 nm on average (twists in the strand may cause somevariation in this length, but we will ignore these for now.) Usingthis information, answer the following questions:

a.What is the minimal number ofamino acids that must be found in a transmembrane ?-strand thatspans the non-polar core of the membrane? (Your answer should be awhole number.)

b. Porins are large channel proteins found in bacteria and inthe outer mitochondrial membranes of eukaryotes. The human porin(also known as the VDAC = voltage-dependent anion channel) has 19transmembrane ?-strands that form a ?-barrel. The porin protein isformed by 283 amino acids. Approximately what percentage of theamino acids (to the nearest whole number) are found in thetransmembrane segments?

c.At the N-terminus of thepolypeptide, there is a segment of 25 amino acids that extends outfrom the membrane and is not part of a ?-strand. Only 1 amino acidextends beyond the membrane surface at the C-terminus. Assumingthat the remaining amino acids form connecting loops of random coilbetween the ?-strands, on average, about how many amino acids arefound in each loop? (Your answer does not need to be a whole numberin this case, but do not exceed one decimal place.)

. The non-polar core of a membrane bilayer is found to be 3.4 nmin thickness. From studies of protein structure, we know that eachamino acid residue in a beta strand extends the length of thestrand by 0.35 nm on average (twists in the strand may cause somevariation in this length, but we will ignore these for now.) Usingthis information, answer the following questions:

a. (1 pts) What is the minimal number of amino acids that mustbe found in a transmembrane ?-strand that spans the non-polar coreof the membrane? (Your answer should be a whole number.)

b. (2 pts) Porins are large channel proteins found in bacteriaand in the outer mitochondrial membranes of eukaryotes. The humanporin (also known as the VDAC = voltage-dependent anion channel)has 19 transmembrane ?-strands that form a ?-barrel. The porinprotein is formed by 283 amino acids. Approximately what percentageof the amino acids (to the nearest whole number) are found in thetransmembrane segments?

c. (2 pts) At the N-terminus of the polypeptide, there is asegment of 25 amino acids that extends out from the membrane and isnot part of a ?-strand. Only 1 amino acid extends beyond themembrane surface at the C-terminus. Assuming that the remainingamino acids form connecting loops of random coil between the?-strands, on average, about how many amino acids are found in eachloop? (Your answer does not need to be a whole number in this case,but do not exceed one decimal place.)