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The alpha helix is the most common helix found in nature. It consists of a coiled polypeptide chain, in which the side chains of the amino acids extend outward from the core, this allows it to maintain its shape. They can be found in many different types of proteins, from globular proteins, such as myoglobin to keratin, which is a fibrous protein. Both these are prodominantly alpha helical in structure. The strength of the helix is determined by the number of disulphide bonds between the different turns of the helix.

It can either be a right-handed or left-handed helice but it has been shown that the right-handed coil is favoured as the side chains do not clash. Hydrogen bonds are formed between the CO of each amino group and the NH of the amino acid four residues prior to it. This gives the alpha-helix stability. There are 3.6 amino acid residues per turn of the alpha-helix coil [1]. Alpha-helices are the main components of Keratin in hair, nails etc as it is flexible and stretchy. Collagen is also made up of coiled alpha-helices and is found in skin, bone cartilage and teeth.

Unlike DNA double stranded helices, the protien alpha-helix is made up of only one strand of polypeptides and is a lot smaller than the DNA double helix.

The alpha-helix is an examply of a secondary structure protein. Another example secondary structure proteins is the beta pleated sheet.

The side chains point out 100oapart [2].


  1. Berg et al., Biochemistry, 6th Edition, New York, W.H. Freeman and Company, 2007
  2. Champe, Pamela C. Biochemistry, 4th Edition. United States of America, Lippincott Williams &Wilkins, 2008.

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