α-Helix There is a repeating pattern in the main chain - the φ/ψ angles are the roughly same from one amino acid to the next generating the slinky structure. Again, note how the N-H bond from one amino acid points directly at the O=C bond of another. This is true all around the cylinder. In many pictures if structures the curly ribbon will represent the mainchain atoms of a helix. The side chains radiate out from the cylinder of the helix. In the demonstration below, the helix is exposed to water on one side and buried in the protein on the other. The polar sidechains generally, can be seen on the water side, while those buried in the protein tend to be hydrophobic.

β-Sheet There is a repeating pattern in the main chain - the φ/ψ angles are the roughly same from one amino acid to the next generating the extended structure. Again, note how the N-H bond from one amino acid points directly at the O=C bond of another - but this time in the other strand of the sheet. In many pictures if structures the arrow ribbon will represent the mainchain atoms of a sheet strand. Notice that tha sidechains project above and below the plane of the sheet alternating...one "up" - one "down" - etc. In the demonstration below, the sheet is exposed to water on one side and buried in the protein on the other. The polar sidechains generally, can be seen on the water side, while those buried in the protein tend to be hydrophobic.

Proline ends helix For the helix in the picture H-bonds can be deduced in the usual places (drawn in orange here). If the top amino acd were not a proline a third anothercould be drawn but instead of a N-H bond pointing at the appropriate C=O a CH₂ from the proline sidechain is directed at it instead, thus no H-bond can be made. This is usually the prime reason for cited for proline ending a helix.

Color definition. Blue=Nitrogen, Gray=Carbon, Red=Oxygen, White=Hydrogen, Yellow/Green=Ribbon, Orange=Hydrogen bonds(Proline structures only)