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.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.)
