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What Is an Alpha Helix?

If an alpha helix breaks, it can cause other local proteins to unwind.
Water molecules may be attracted to one side of an alpha helix beta sheet and repelled by the other.
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  • Written By: Andrew Kirmayer
  • Edited By: Allegra J. Lingo
  • Last Modified Date: 22 June 2014
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Proteins are essential for life and come in many forms. Their structure can vary, which can have a significant effect on the functions of amino acids and various biological functions. An alpha helix is comprised of a chain of amino acids bonded by hydrogen, classifying the helix as a secondary protein structure. It is typically 10 amino acids long and has properties that are similar to a spring. Forces that can break the bonds can damage a single helix as well as the structure of cells and the binding of deoxyribonucleic acid (DNA).

If an alpha helix breaks, it can cause other local proteins to unwind. Cellular functions and higher biological functions can be disrupted. Alpha helices store energy in their bonds, and it takes a force strong enough to break each bond to cause the structures to unravel their shape. They come in various motifs, such as helix-turn-helix motifs, and have a diameter that is equal to that of a groove in DNA.

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The protein alpha helix serves as a structurally supporting component for DNA, and for cellular cytoskeletons on a larger scale. On larger biological dimensions, alpha helices are important in the construction of hair as well as wool and hooves. They also serve a role in the composition of other structures, such as the alpha helix beta sheet, in which two or more chains of amino acids sit in parallel. There are multiple hydrogen bonds that form in between the strands of the beta sheet to form a rigid structure. One side can be resistant to water molecules, while the other is charged and able to interact with or be altered by water.

Polar charge is a contributing factor to stability. An alpha helix is typically positively charged on one end and negatively charged on the other, which can destabilize the structure. A negatively charged amino acid ordinarily sits at the positive end, but sometimes a positively charged protein is found at the negative end instead. Either arrangement stabilizes the helix and keeps it intact.

Each alpha helix is submicroscopic but features a degree of mechanical durability, even at the molecular level. A certain level of elasticity and strength is attributed to the proteins, but the effect of mechanical load on these structures is not fully understood. How any deformation or failure happens is not known, but if breakage and unwinding occurs, it can be detrimental to cells and the biological functions of organisms.

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