Editing Protein folding (section)

=== Secondary structure ===
{{Main|Protein secondary structure}}
[[File:Alpha helix.png|thumb|332x332px|The [[alpha helix]] spiral formation]]
[[File:BetaPleatedSheetProtein.png|left|thumb|150x150px|An anti-parallel [[beta pleated sheet]] displaying hydrogen bonding within the backbone]]

Formation of a [[Protein secondary structure|secondary structure]] is the first step in the folding process that a protein takes to assume its native structure. Characteristic of secondary structure are the structures known as [[alpha helix|alpha helices]] and [[beta sheet]]s that fold rapidly because they are stabilized by [[Intramolecular force|intramolecular]] [[hydrogen bond]]s, as was first characterized by [[Linus Pauling]]. Formation of intramolecular hydrogen bonds provides another important contribution to protein stability.<ref name="Rose">{{cite journal | vauthors = Rose GD, Fleming PJ, Banavar JR, Maritan A | title = A backbone-based theory of protein folding | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 45 | pages = 16623–33 | date = November 2006 | pmid = 17075053 | pmc = 1636505 | doi = 10.1073/pnas.0606843103 | bibcode = 2006PNAS..10316623R | citeseerx = 10.1.1.630.5487 | doi-access = free }}</ref> α-helices are formed by hydrogen bonding of the [[Backbone chain|backbone]] to form a spiral shape (refer to figure on the right).<ref name="Voet_2016" /> The β pleated sheet is a structure that forms with the backbone bending over itself to form the hydrogen bonds (as displayed in the figure to the left). The hydrogen bonds are between the amide hydrogen and carbonyl oxygen of the [[peptide bond]]. There exists anti-parallel β pleated sheets and parallel β pleated sheets where the stability of the hydrogen bonds is stronger in the anti-parallel β sheet as it hydrogen bonds with the ideal 180 degree angle compared to the slanted hydrogen bonds formed by parallel sheets.<ref name="Voet_2016" />