Alpha helix
Videos
An alpha helix is a sequence of amino acids in a protein that are twisted into a coil.
Contrast of helix end views between α (offset squarish) vs 310 (triangular)
Ramachandran plot (φ, ψ plot), with data points for α-helical residues forming a dense diagonal cluster below and left of center, around the global energy minimum for backbone conformation.
An α-helix in ultrahigh-resolution electron density contours, with oxygen atoms in red, nitrogen atoms in blue, and hydrogen bonds as green dotted lines (PDB file 2NRL, 17–32). The N-terminus is at the top, here.
Leucine zipper coiled-coil helices & DNA-binding helices: transcription factor Max (PDB file 1HLO)
Hydrogen bond
Videos
In chemistry, a hydrogen bond is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen at
AFM image of naphthalenetetracarboxylic diimide molecules on silver-terminated silicon, interacting via hydrogen bonding, taken at 77 K. ("Hydrogen bonds" in the top image are exaggerated by artifacts of the imaging technique.)
An example of intermolecular hydrogen bonding in a self-assembled dimer complex. The hydrogen bonds are represented by dotted lines.