How does primary structure differ from secondary structure in proteins?

In biochemistry, the primary and secondary structures represent different levels of protein organization:

• Primary Structure: This refers exclusively to the linear amino acid sequence of a protein's peptide chains. It is defined without regard for the spatial arrangement or conformation of the chain.1
• Secondary Structure: This refers to the local spatial arrangement of the main peptide chain. It is determined by the folding of the chain into regular patterns—such as the α-helix or the β-pleated sheet—stabilized by hydrogen bonds between the carbonyl and imino groups of the peptide backbone. Crucially, secondary structure is defined without considering the conformation of the amino acid side chains or other segments of the protein.123

While the primary structure provides the fundamental sequence, the secondary structure describes the resulting geometric shapes formed by the backbone of that sequence.1