The beta-sheet forms hydrogen bonds with neighboring amino acid chains, not within itself. Appear pleated due to the hydrogen bonding.
-Antiparallel - where the chains are hydrogen bonded in opposite directions
-Parallel – chains are hydrogen bonded in the same direction 


Grand Valley State University

Secondary protein structure refers to only the spatial arrangements of the polypeptide backbone that does not include the sided chain conformations. 
The most common secondary structures include:
-	Alpha helix
-	Beta sheets
- Turns

Secondary Protein Structure

Voet, D., Voet, J. G., & Pratt, C. W. (2013). Chapter 6: Proteins: Three-Dimensional Structure. In Fundamentals of biochemistry: Life at the molecular level (4th ed., pp. 127-175). Hoboken, NJ: Wiley. Retrieved January 05, 2021, from archive.org.

Fundamental of biochemistry: Life of the molecular level 4th edition: Chapter 6

The alpha helix is a right-handed and has a backbone consisting of hydrogen bonds binding to each 4th amino acid residue. There are about 3.6 residues for each turn. 

The Alpha Helix

The Beta Sheet

Turns are polypeptide sequences that connect secondary structures (i.e. alpha helices and beta sheets). There are two types of arrangements for turns: 
- Type I
- Type II

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