secondary structure

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The protein structure characterized by folding of the peptide chain into an alpha helix, beta sheet, or random coil.
• noun The folded, helical structure of double-stranded DNA.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biochemistry The general three-dimensional structure of a biopolymer such as DNA or a protein.