General Chemistry

The Protein Subunit

Each subunit in Figure 2 contains regions with a coiled shape; many of the amino acids that make up the polypeptide chain interact to form this particular structure, called an alpha helix. In an alpha helix (Figure 3), each amino acid is "hydrogen-bonded" to the amino acid that is four residues ahead of it in the chain. In hemoglobin, the hydrogen-bonding interaction occurs between the H of an -NH group and the O of a -CO group of the polypeptide backbone chain; the amino-acid side chains extend outward from the backbone of the helix. Approximately 75% of the amino-acid composition of hemoglobin adopts an alpha-helical structure. Another common structural motif is the beta-pleated sheet, in which amino acids line up in straight parallel rows.

Hydrogen Bond

Figure 3

This is a molecular model of the alpha-helix structure in a subunit of hemoglobin. The blue strands are a ribbon representation to emphasize the helical structure. The green dotted lines show the hydrogen bonding between the -NH and -CO functional groups.

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Note: To view the molecule interactively, please use Jmol, and click on the button above.

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View Movie

Please click on the pink button above to view a QuickTime movie showing a rotation of the alpha-helix structure shown in Figure 3.

Click the blue button below to download QuickTime to view the movie.


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This page created by Matt Traverso, Washington University in St Louis.
© 2004, Washington University.
Materials and Information present may be reproduced for educational purposes only.

Revised: 2004-08-08