Editing Protein secondary structure (section)

== Experimental determination ==
The rough secondary-structure content of a biopolymer (e.g., "this protein is 40% [[alpha helix|α-helix]] and 20% [[beta sheet|β-sheet]].") can be estimated [[spectroscopy|spectroscopically]].<ref name="Pelton_ McLean_2000">{{cite journal | vauthors = Pelton JT, McLean LR | title = Spectroscopic methods for analysis of protein secondary structure | journal = Anal. Biochem. | volume = 277 | issue = 2 | pages = 167–76 | year = 2000 | pmid = 10625503 | doi = 10.1006/abio.1999.4320 }}</ref> For proteins, a common method is far-ultraviolet (far-UV, 170–250&nbsp;nm) [[circular dichroism]]. A pronounced double minimum at 208 and 222&nbsp;nm indicate α-helical structure, whereas a single minimum at 204&nbsp;nm or 217&nbsp;nm reflects random-coil or β-sheet structure, respectively. A less common method is [[infrared spectroscopy]], which detects differences in the bond oscillations of amide groups due to hydrogen-bonding. Finally, secondary-structure contents may be estimated accurately using the [[chemical shift]]s of an initially unassigned [[nuclear magnetic resonance|NMR]] spectrum.<ref name="pmid14668443">{{cite journal | vauthors = Meiler J, Baker D | title = Rapid protein fold determination using unassigned NMR data | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 100 | issue = 26 | pages = 15404–09 | year = 2003 | pmid = 14668443 | pmc = 307580 | doi = 10.1073/pnas.2434121100 | bibcode = 2003PNAS..10015404M | doi-access = free }}</ref>