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Alpha Helix and Beta-Pleated Sheet

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Last updated date: 11th Jul 2024
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An Introduction of Alpha and Beta-Pleated Sheet

In this definition of alpha helix, sheets are characterised through their tight pleats, while in beta pleated sheets, they have looser pleats. Additionally, alpha helix sheets are much less likely to stretch than beta pleated sheets. Alpha-Helix forms all possible hydrogen bonds by twisting into a right handed screw (helix) with the –NH group of each amino acid residue hydrogen bonded to the >C=O of an adjacent turn of the helix.

Beta-pleated sheet structure resembles the pleated folds of drapery.

Helix Meaning

Helix is something spiral in shape that is coiled and contains a repeating pattern. It is a kind of smooth space urve with tangent lines at a constant angle to a fixed axis. Helices are necessary in biology, as the DNA molecule is created as two intertwined helices. Lots of proteins have helical substructures, called alpha helices.

What is Protein?

Protein is a giant, complicated molecule that performs a critical function in our body. It does maximum of the cells' paintings and is needed to shape, feature, and adjust the body’s tissues and organs. Protein is a product of loads or hundreds of long-chain smaller amino acids. The series of amino acids determines the shape and feature of the protein.

Types of Protein

According to their structure, proteins are classified into three types. They are:

  • Primary Protein: The primary structure of a protein is outlined as the sequence of amino acids connected together to make a polypeptide chain.

  • Secondary Protein: The next level of protein structure, secondary structure, refers to local folded structures that form inside a polypeptide due to interactions between atoms. The most common forms of secondary structures are the α helix and the and the sheet.

  • Tertiary Protein: The three-dimensional structure of a polypeptide is termed its tertiary structure.

Primary Protein

The linear sequence of amino acids inside a protein is considered the protein’s primary structure. Each protein features a distinctive primary structure that varies in the pattern amino acids are arranged and the total number of amino acids present within the protein molecule.

Secondary Protein

Secondary protein is often described through intermolecular hydrogen bonds. Alpha-Helices and Beta-Pleated sheets are examples of the secondary shape of the protein.

Alpha-Helix Protein

The most common variety of secondary structure of a protein is the alpha-helix. In the alpha-helix protein, a H bond is created between the N−H group to the C=O group of the amino acid.

The alkyl groups of the alpha-helix chain aren't involved within the H bonds; however, they maintain the alpha-helix structure. Every winding turn in an alpha helix has 3.6 amino acid residues.

Alpha Helix and Beta Pleated Sheet

Alpha-Helix and Beta-Pleated sheets are forms of the secondary shape of the protein. In this arrangement, the polypeptide chains are extended beside one another and then bonded by intermolecular H-bonds. In this structure, all peptide chains are stretched out to almost maximum extension then laid side by side which is held along by intermolecular H bonds. The structure resembles the pleated folds of drapery and thus is known– a beta-pleated sheet.

Protein’s Secondary Structure

Protein’s Secondary Structure

Beta-Pleated Sheets of Protein

The second important type of secondary form of a protein is the Beta-Pleated Sheets of protein. The beta pleated structure of proteins includes various beta strands connected with the help of using H bonds among adjoining strands. 3 to 10 amino acids are mixed to create a beta-strand polypeptide.

Difference Between Alpha and Beta Helix

The difference between alpha helix and beta sheet on the basis of their definition, shape, formations and bonds are listed in the following table:

Alpha Helix

Beta Helix

Alpha helix shows intramolecular H bonding.

Beta-helix shows intermolecular H bonding.

The alpha helix forms a right-handed helix.

Beta-helix can form each right and left-handed helices.

The twisting of the amino acid sequence results in the formation of alpha helix.

In beta-helix formation, the 2 beta sheets either parallelor antiparallel are bound to form the helical structure.


Complex proteins have 3 structural organisational levels – primary, secondary, and tertiary. The secondary structures of proteins form the amide chains in several orientations. The peptide chains comprises amino acid sequences bound by amide bonds. Therefore, there are 2 main secondary structures in proteins which are alpha helix and beta helix. This article focuses on the difference between alpha and beta-helix .

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FAQs on Alpha Helix and Beta-Pleated Sheet

1. What are the similarities between alpha and beta helix?

The similarities between alpha and beta-helix are as follows: Alpha and Beta Helix are 2 secondary structures of proteins. Amino acids are the monomers of both secondary structures. Moreover, the chemical constituents of the alpha and beta helices are carbon, hydrogen, oxygen, nitrogen, and sulphur. Also, both secondary structures change into a higher-level organisation. Moreover, each is stabilised by H bonds. In each structure, the hydrophobicity is determined by the presence of the R groups of the amino acids.

2. What is the quaternary structure of protein ?

The quaternary structure of a protein is the association of many protein chains or subunits into a closely packed arrangement. Each of the subunits has its primary, secondary, and tertiary structure. The subunits are held together by H bonds and Van der Waals forces between nonpolar side chains. 

3. Where does the quaternary structure of protein occur and how is it important?

Quaternary structure exists in proteins consisting of 2 or more identical or different polypeptide chains (subunits). These proteins are known as oligomers because they have 2 or more subunits. The quaternary structure describes how subunits are arranged in the native protein. Quaternary structure is an important part that contributes to the sophisticated allosteric regulation mechanism in a key catalyst from Mycobacterium tuberculosis. The dimer is the simplest quaternary structure; it's just 2 subunits. "homodimer" describes  the similarities of its subunits.