Primary structure of proteins refer to the sequence in which the amino acids are arranged in them. Proteins have specific sequence of amino acids which are essential for a particular biological activity. The change in even one amino acid can alter the biological activity.
Secondary structures of protein refer to the arrangement of the polypeptide chain giving rise to a particular shape, which arises due to hydrogen bonding.
The two common secondary structures of proteins are α-helix and β-pleated sheet structure.
An α helix is a right-handed helix that is held together by hydrogen bonding. In this structure the hydrogen bond is formed between the N-H on one amino acid and the C=O on another amino acid 4 residues away.
The β sheet is formed when beta strands are linked together by hydrogen bonds, forming a pleated sheet of amino acid residues. Again, the hydrogen bonds are between the N-H group of one amino acid and the C=O group of another.
Structures of α-helix and β-pleated sheet.
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