Question

What is meant by the secondary structure of proteins?

Answer 1

Proteins:

• They are organic molecules that are composed of long chains of amino acids.
• Proteins are present in many essential biological compounds such as enzymes.
• Peptides are short chains of amino acids linked by peptide bonds.
• A polypeptide is a longer/continuous/unbranched peptide chain.

Secondary structure of proteins:

• The secondary structure of a protein refers to the shape in which a long polypeptide chain can exist.
• The secondary structures of proteins exist in two forms:

1. $\mathrm{\alpha }-$Helix
2. $\mathrm{\beta }-$sheets

$\mathrm{\alpha }-$Helix:

• "$\mathrm{\alpha }-$Helix is one of the most common ways in which a polypeptide chain forms all possible hydrogen bonds by twisting into a right-handed screw (helix) with the $–\mathrm{NH}$ group of each amino acid residue hydrogen-bonded to the $\mathrm{C}=\mathrm{O}$ of an adjacent turn of the helix.":

$\mathrm{\beta }-$sheets:

• “In $\mathrm{\beta }-$pleated sheet structure, all peptide chains are stretched out to nearly maximum extension and then laid side by side which is held together by intermolecular hydrogen bonds.”

The structure of $\mathrm{\alpha }-$Helix and of $\mathrm{\beta }-$sheets are shown below.