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Alpha-Helix and Beta-Sheet

Alpha-Helix and Beta-Pleated sheets are types of the secondary structure of the protein.

They both are shaped by hydrogen bonding between the carbonyl O of one amino acid and the amino H of another.

This section will discuss the protein, types of protein, and the primary and secondary protein structures, i.e. alpha-helix and beta-pleated sheets.

Table of Content

What is a Protein?

Protein is a giant, complex molecule that plays an essential role in our body. It does most of the cells work and is required to structure, function, and regulate the body’s tissues and organs.

Protein is made of hundreds or thousands of long-chain smaller amino acids. The sequence of amino acids determines the structure and function of the protein. Twenty different types of amino acids are combined to create a protein.

Types of Protein

Based on structure, we can divide protein into two types:

  • Primary Protein
  • Secondary Protein

Primary Protein

The linear sequence of amino acids within a protein is considered the protein’s primary structure.

Each protein has a distinctive primary structure that varies in the pattern amino acids are arranged and the total number of amino acids present in the protein molecule.

Haemoglobin is an example of primary protein.

Secondary Protein

Secondary Protein is the three-dimensional form of local protein segments. It is primarily defined by hydrogen bonds between amino acids and carboxyl oxygen atoms.

Alpha-Helix and Beta-Pleated sheets are types of the secondary structure of the protein.

Alpha-Helix Protein,

The most common type of secondary structure of a protein is the alpha-helix.

Linus Pauling predicted the structure of the alpha-helix protein. The prediction was confirmed when the first three-dimensional structure of protein myoglobin was determined by X-ray crystallography.

In the alpha-helix protein, a hydrogen bond is formed between the N−H group to the C=O group of the amino acid.

The alkyl groups of the alpha-helix chain are not involved in the H bonds but maintain the alpha-helix structure. Every winding turn in an alpha helix has 3.6 amino acids residues.

Beta-Pleated Sheets of Protein

The second essential type of secondary structure of a protein is the Beta-Pleated Sheets of Protein. It consists of various beta strands linked by hydrogen bonds between adjacent strands. Three to ten amino acids are combined to create a beta-strand polypeptide.

Beta sheets are involved in forming the fibrils and protein aggregates observed in amyloidosis.

Alike alpha-helix, the residue hydrogen bond between the adjacent strands are separate from each other.

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 acids 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 cant is 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

What is a Protein?

Protein is a giant, complex molecule that plays an essential role in our body. It does most of the cells work and is required to structure, function, and regulate the body’s tissues and organs.

Protein is made of hundreds or thousands of long-chain smaller amino acids. The sequence of amino acids determines the structure and function of the protein. Twenty different types of amino acids are combined to create a protein

What is a secondary protein?

Secondary Protein is the three-dimensional form of local segments of the protein. It is primarily defined by hydrogen bonds between amino acids and carboxyl oxygen atoms.

Alpha-Helix and Beta-Pleated sheets are types of the secondary structure of the protein.

What is an alpha helix protein?

The most common type of secondary structure of the protein is the alpha-helix.

In the alpha-helix protein, a hydrogen bond is formed between the N−H group to the C=O group of the amino acid.

The alkyl groups of the alpha-helix chain are not involved in the H bonds but maintain the alpha-helix structure. Every winding turn in an alpha helix has 3.6 amino acids residues.

What is a beta-pleated sheet of protein?

Beta-Pleated Sheets of Protein is a type of secondary structure of a protein. It consists of various beta strands linked by hydrogen bonds between adjacent strands. Three to ten amino acids are combined to create a beta-strand polypeptide.

Beta sheets are involved in forming the fibrils and protein aggregates observed in amyloidosis.

Alike alpha-helix, the residues hydrogen bond between the adjacent strands are separate from each other.

Give differences between alpha-helix and beta-pleated protein?

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 acids 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 cant is 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.

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