Secondary Structure of Protein

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The illustration shows an alpha helix protein structure, which coils like a spring, and a beta-pleated sheet structure, which forms flat sheets stacked together. In an alpha-helix, hydrogen bonding occurs between the carbonyl group of one amino acid and the amino group of the amino acid that occurs four residues later. In a beta-pleated sheet, hydrogen bonding occurs between two different lengths of peptide that are antiparallel to one another.
The α-helix and β-pleated sheet are secondary structures of proteins that form because of hydrogen bonding between carbonyl and amino groups in the peptide backbone. Certain amino acids have a propensity to form an α-helix, while others have a propensity to form a β-pleated sheet.

Source: OpenStax Biology 2e

OpenStax Biology 2e

The local folding of the polypeptide in some regions gives rise to the secondary structure of the protein. The most common are the α-helix and β-pleated sheet structures. Both structures are held in shape by hydrogen bonds. The hydrogen bonds form between the oxygen atom in the carbonyl group in one amino acid and another amino acid that is four amino acids farther along the chain.

Every helical turn in an alpha helix has 3.6 amino acid residues. The polypeptide’s R groups (the variant groups) protrude out from the α-helix chain. In the β-pleated sheet, hydrogen bonding between atoms on the polypeptide chain’s backbone form the “pleats”. The R groups are attached to the carbons and extend above and below the pleat’s folds. The pleated segments align parallel or antiparallel to each other, and hydrogen bonds form between the partially positive nitrogen atom in the amino group and the partially negative oxygen atom in the peptide backbone’s carbonyl group. The α-helix and β-pleated sheet structures are in most globular and fibrous proteins and they play an important structural role.

– What is a common motif of regular secondary structure in proteins which consist of beta strands (also β-strand) connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet?

A Ramachandran plot originally developed in 1963 by G. N. Ramachandran, C. Ramakrishnan, and V. Sasisekharan is a way to visualize energetically allowed regions for backbone dihedral angles ψ against φ of amino acid residues in protein structure.


Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: