Alpha-Helix and Beta-sheets are forms of the protein’s secondary structure.
The carbonyl O of one amino acid forms hydrogen bonds with the amino H of another.
This section will address proteins, protein types, and the primary and secondary protein structures, including the alpha-helix and beta-pleated sheets.
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What is a Protein?
Protein is a large, complicated molecule that serves a crucial function in the human body. It is essential for the structure, function, and regulation of the body’s tissues and organs and performs the majority of the cell’s tasks.
Hundreds of thousands of long-chain, smaller amino acids compose a protein. The sequence of amino acids controls the protein’s structure and function. Twenty distinct amino acid types are combined to form a protein.
Types of Protein
On the basis of their structure, proteins can be divided into two classes:
- Primary Protein
- Secondary Protein
Primary Protein
The main structure of a protein is the linear sequence of amino acids contained inside it.
Each protein has a unique fundamental structure that differs in the arrangement of amino acids and the number of amino acids contained in the molecule.
Haemoglobin is a fundamental protein example.
Secondary Protein
Local protein segments are represented in their three-dimensional form by secondary protein. Hydrogen bonding between amino acids and carboxyl oxygen atoms characterize it primarily.
Alpha-Helix and Beta-Pleated sheets are forms of the protein’s secondary structure.
Alpha-Helix Protein
The alpha-helix is the most prevalent form of secondary structure in proteins.
Linus Pauling predicted the alpha-helix protein structure. When the first three-dimensional structure of the protein myoglobin was determined using X-ray crystallography, the prediction was confirmed.
In the alpha-helix protein, the NH group forms a hydrogen bond with the C=O group of the amino acid.
The alkyl groups of the alpha-helix chain are not engaged in the H bonding, but they keep the structure of the alpha-helix intact. Each turn of an alpha helix contains 3.6 amino acid residues.
Beta-Pleated Sheets of Protein
Beta-Pleated Protein Sheets are the second fundamental form of secondary protein structure. It is composed of several beta strands connected by hydrogen bonds. A beta-strand polypeptide is produced by combining three to 10 amino acids.
In amyloidosis, beta sheets are involved in the formation of fibrils and protein clumps.
Similar to alpha-helix, the residue hydrogen bonds between adjacent strands are distinct.
Differences between Alpha-Helix and Beta-Sheet
| S No. | Alpha-Helix | Beta-Sheet |
| 1 | Amino acids exist in the right-handed coiled rod-like structure. | Amino acids exist in an almost entirely extended conformation, i.e. linear or sheet-like structure. |
| 2 | Intramolecular hydrogen bonding forms within the polypeptide chain to create a spiral structure. | Beta sheets are formed by linking two or more beta strands by intermolecular hydrogen bonds. |
| 3 | 3.6 amino acid residues are winded to form an alpha-helix polypeptide. | Three to ten amino acids are combined to form a beta-strand polypeptide. |
| 4 | Alpha-Helix can be a single-chain polypeptide. | Beta-Sheet cannot be in a single-chain Polypeptide. There must be two or more beta strands. |
| 5 | Alkyl groups of alpha-helix are oriented outside of the helix. | Alkyl groups are oriented both inside and outside of the sheet. |
| 6 | Example: Keratin, Myoglobin and Haemoglobin. | Example: Skin Fibres or Fibroin. |
Frequently Asked Questions on Alpha-Helix and Beta-Sheet
Q.1 What is a Protein?
Protein is a large, complicated molecule that serves a crucial function in the human body. It is essential for the structure, function, and regulation of the body’s tissues and organs and performs the majority of the cell’s tasks.
Hundreds of thousands of long-chain, smaller amino acids compose a protein. The sequence of amino acids controls the protein’s structure and function. Twenty distinct amino acid types combine to produce a protein.
Q.2 What is a secondary protein?
Secondary Protein is the three-dimensional structure of local protein fragments. Hydrogen bonding between amino acids and carboxyl oxygen atoms characterize it primarily.
Alpha-Helix and Beta-Pleated sheets are forms of the protein’s secondary structure.
Q.3 What is an alpha helix protein?
The most prevalent kind of protein secondary structure is the alpha-helix. In the alpha-helix protein, the NH group forms a hydrogen bond with the C=O group of the amino acid.
The alkyl groups of the alpha-helix chain are not engaged in the H bonding, but they keep the structure of the alpha-helix intact. Every alpha helix turn contains 3.6 amino acid residues.
Q.4 hat is a beta-pleated sheet of protein?
Beta-Pleated Sheets of Protein are a form of protein’s secondary structure. It is composed of several beta strands connected by hydrogen bonds. A beta-strand polypeptide is produced by combining three to 10 amino acids.
In amyloidosis, beta sheets are involved in the formation of fibrils and protein clumps.
Similar to alpha-helix, the residues that form hydrogen bonds across adjacent strands are distinct from one another.
