Sequence Analysis:
1) alpha-helices (20aa without proline or glycine present) and beta-bends (proline with a small aa before or after it, like glycine or alanine) can be somewhat reliably predicted from reading the sequence of aa's. Out in the research world, many people are working on mathematical algorithms that can more reliably predict the folding for the other types of secondary structures.
2) Antiparallel and parallel beta-strands.
3) In a beta-pleated sheet, the sideschains are oriented above and below the plane of the sheet.
4) The antiparallel sheet should have linear hydrogen bonding while the parallel sheet should have slightly off-center/skewed hydrogen bonding. Just make sure you line up the backbone correctly. The antiparallel beta-sheet should be stronger because the hydrogen bonds are stronger when they are linear. The sidechains are extending outside of the sheet, projecting above and below the plane of the beta-sheet.
5) I must admit to you that I thought this was a pretty straightforward question. Now I realize that the answer requires consideration of many, many elements that contribute to structural strength. Alpha-helices and antiparallel beta-sheets both have linear hydrogen bonding between every backbone NH and CO group (as long as the sheet has more than two strands). So, you could consider the strength based on hydrogen bonding equal, all other things being equal. But what about those other issues? Sidechains and their placement, exposure (or lack of) to water, the length of the helix, the number of strands in the sheet, etc. Go ahead and think about the possible contributing factors. And, I hope you'll be as amazed as I was by the variety of elements that go into the stabilization of protein structure.
6) From your problems book, see answer for Peptides and Proteins #14.
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