Amino acids are molecules with the general structure shown below, where R can be H or various groups of bonded atoms. The 20 different R groups reflect the 20 naturally occurring amino acids. Although amino acids overall are polar, their relative polarity and relative degree of interaction with other substances is governed by the R group. 

Amino acids bond together (like "chains") to form proteins, which exhibit complex 3-dimensional structures resulting from various folds,   twists, and turns of the amino acid "chains". These specific structures   occur to provide very specific functions of the protein in an organism. 

Ferritin is a protein that stores iron in its core as Fe+3 and releases the Fe as Fe+2 for use in reactions elsewhere in an organism. The iron as Fe+2 (technically in a more complicated form, but we'll treat it as a simple ion) travels to and from the protein core via two major channels, a 3-fold and a 4-fold channel, illustrated below

3-fold channel  4-fold channel  (substances enter through the central hole)

The 3-fold channel is lined primarily with the amino acids aspartic acid and glutamic acid, illustrated below. The 4-fold channel is lined primarily with the amino acid leucine, also illustrated below. 

Lines 3-fold channel Lines 3-fold channel Lines 4-fold channel

(a) Into which channel is Fe2+ most likely to travel? Briefly explain your answer by including the dominant interparticle force between it and the amino acid R groups that line the channel.

(b) Into which channel is O2 most likely to travel? Briefly explain your answer by including the dominant interparticle force between it and the amino acid R groups that line the channel.

(c) Suppose there is a region in a protein where a significant amount of H bonding occurs between R groups of amino acids. Which of the amino acids on the previous page could you expect to be present in such a region? Illustrate one possible H bonding interaction between R groups of the amino acid(s) you chose. 

How do I solve these questions?