Alpha Helix and Beta Sheet

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∟Alpha Helix and Beta Sheet

This section provides a quick introduction of protein secondary structures, alpha helix and beta sheet. Both structures are stabilized by hydrogen bonds between oxygen atoms and hydrogen atoms of two amino acid residues lined up side by side.

What Is Alpha Helix? - An alpha helix is a secondary structure in a protein, where a section of the protein sequence is twisted into a coil conformation. The oxygen of the carboxylic acid group of an amino acid residue is lined up to the hydrogen of the amino group of another amino acid residue located one circle away on the coil conformation to form a hydrogen bond.

Those hydrogen bonds keep an alpha helix stabilized.

The picture below provides a good illustration of an alph helix (source: researchgate.net):

Protein Secondary Structure - Alpha Helix

What Is Beta Sheet? - A beta sheet is a secondary structure in a protein, where a section of the protein sequence is positioned side by side with another section of the protein sequence into a pleated sheet conformation. The oxygen of the carboxylic acid group of an amino acid residue is lined up to the hydrogen of the amino group of another amino acid residue from the adjacent section on the pleated sheet conformation to form a hydrogen bond.

Those hydrogen bonds keep a beta sheet stabilized.

The picture below provides a good illustration of a beta sheet formed with 3 sections of the protein sequence (source: researchgate.net):

Protein Secondary Structure - Beta Sheet

If two adjacent sections of the protein sequence in a beta sheet are running in the same direction from N-terminal to C-Terminal, they have a parallel beta sheet relation. For example, the top two sections of the protein sequence in the above picture have a parallel beta sheet relation.

If two adjacent sections of the protein sequence in a beta sheet are running in different directions from N-terminal to C-Terminal, they have an anti-parallel beta sheet relation. For example, the bottom two sections of the protein sequence in the above picture have an anti-parallel beta sheet relation.