A composite showing the original ribbon-drawing representations for helix, sheet, and loops.  Taken from drawings by Jane Richardson (User:Dcrjsr).
<a href="//commons.wikimedia.org/wiki/User:Dcrjsr" title="User:Dcrjsr">Dcrjsr</a>
CC BY 4.0
<span class="int-own-work" lang="en">Own work</span>