Alpha helix

An alpha helix is a common protein secondary structure in which a polypeptide backbone coils into a right-handed spiral, stabilized by hydrogen bonds between backbone groups.

Protein backbone: The repeating chain of atoms linking amino acids in a protein, excluding their variable side chains. Its peptide bonds and atoms form the helical scaffold.
Protein: A molecule made of one or more folded chains of amino acids. Alpha helices are recurring structural elements within proteins.
Beta sheet: A protein secondary structure formed by extended strands linked through hydrogen bonds. It uses backbone hydrogen bonds like an alpha helix but arranges chains into sheets.
Coiled coil: A protein structure in which two or more alpha helices wrap around one another. It uses alpha helices as building blocks for stable assemblies.
Hydrogen bond: An attraction involving a hydrogen atom bonded to an electronegative atom and another electronegative atom. These interactions link backbone groups along the helix.
Amino acid: An organic molecule with amino and carboxyl groups that serves as a protein building block. Amino-acid sequence determines which helical structures a protein can form.
3₁₀ helix: A protein helix with three residues per turn and hydrogen bonds spanning three residue intervals. Its tighter geometry contrasts with the more common alpha-helical pattern.
Transmembrane helix: An alpha helix that crosses a biological membrane, often with hydrophobic side chains facing lipids. This specialized helix spans the membrane’s hydrophobic interior.
Peptide bond: The covalent amide bond joining amino acids in a polypeptide chain. Its partial double-bond character restricts backbone rotation and shapes helical geometry.
Protein secondary structure: Local, recurring arrangements of a protein’s backbone, including helices and sheets. The alpha helix is a defining type of this structural level.

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