Question

. 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.)