alpha helixn. A secondary structure of proteins, characterized by a single, spiral chain of amino acids stabilized by hydrogen bonds.[From alpha-form, the form taken by unstretched protein molecules.]al?pha-hel?i·cal (-h?l??-k?l, -h??l?-) adj.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.alpha helix n (Biochemistry) biochem a helical conformation of a polypeptide chain, found abundantly in the structure of proteins Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014al?pha he?lix n. the spatial configuration of many protein molecules in which the polypeptide backbone is stabilized by hydrogen bonds between amino acids in successive helical turns. [1950?55] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.