Question

Which level of protein organisation is exemplified by $\alpha$-helices and $\beta$-sheets?

• A. Primary structure
• B. Secondary structure
• C. Tertiary structure
• D. Quaternary structure

Answer 1

The correct option is B Secondary structure

The primary structure refers to the number and sequence of amino acids in a polypeptide.

The folding of the polypeptide chain in different ways gives rise to its secondary structure. ⍺-helix is the most common type of coil in which the polypeptide folds. Proteins such as keratin, myosin are present as ⍺-helices. Another type of secondary structure is represented by 𝛽-sheets. Here, the polypeptide chains are bonded with the help of hydrogen bonding through their backbone. The chains can occur in a parallel or antiparallel fashion.

Tertiary structure refers to the further coiling and folding of the secondary structure upon itself like a hollow woollen ball or mass.

The quaternary structure involves the aggregation of two or more polypeptide chains or subunits in their tertiary form together in a particular fashion. Each polypeptide develops its own tertiary structure. It includes the number and kinds of subunits in protein, together with their relative position with respect to each other.