Alpha Helix Pitch and Rise

Practice: How many amino acid residues are needed for the α-helix backbone to obtain exactly one full periodic repeat?

Practice: Suppose a cell membrane is 45 Å thick & an embedded protein has 7 parallel transmembrane α-helical segments. Calculate the minimum # of aa-residues required for all 7 α-helical segments to traverse the membrane.

Practice: Hair is predominantly made of α-helix structures. Suppose hair grows at a rate of 20 cm/year. What is the rate at which amino acid residues are synthesized to account for the indicated growth of hair?