Question

Explain the terms primary and secondary structure of proteins. What is the difference between $\alpha$-helix and $\beta$-pleated sheet structure of proteins?

Answer 1

Primary and secondary structures of protein

Proteins may have one or more polypeptide chains, Each polypeptide in a protein has amino acids linked with each other in a specific sequence and this sequence of various amino acids is said to be the primary structure of that protein.

Secondary structure of proteins

The secondary structure of protein refers to the shape in which a long polypeptide chain can exist. They are found to exist in two different types of structures viz. $\alpha$-helix and $\beta$-pleated sheet structure. These structures arise due to the regular folding of the backbone of the polypeptide chain due to hydrogen bonding between
$>C=Oand–NH$ groups of the peptide bond.

Difference between $\alpha$-helix and $\beta$-pleated sheet structure of proteins

$\begin{array}{cc}\alpha -helix& \beta -pleatedsheet\\ \text{Right-handed coiled rod-like structure}& \text{Sheet-like structure}\end{array}$

$\begin{array}{cc}\alpha -helix& \beta -pleatedsheet\\ \text{Intramolecular hydrogen bonding within the polypeptide chain}& \text{Intermolecular hydrogen banding between two separate polypeptide chains}\end{array}$

$\begin{array}{cc}\alpha -helix& \beta -pleatedsheet\\ \text{Hydrogen bands form between the -NH group of each amino acid residue and the >C=O of an adjacent turn of the helix}& \text{Hydrogen bonds form between the- NH and >C-0 groupsof adjacent peptide chains}\end{array}$