Alpha-helix is found in which level of protein structure ?

Step-by-step solution

The primary structure of a protein refers to the linear sequence of amino acids. The secondary structure refers to the local folded structures that form within a polypeptide due to interactions between atoms of the backbone. The most common types of secondary structures are the -helix and the -pleated sheet. The tertiary structure is the overall three-dimensional structure of a polypeptide. The quaternary structure is the arrangement of multiple folded protein or coiling protein molecules in a multi-subunit complex