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Primary structure is simply the sequence of amino acids in a polypeptide chain. For example, the hormone insulin has two polypeptide chains. Each chain has its own set of amino acids, assembled in a particular order.

Secondary structure refers to local folded structures that form within a polypeptide chain.secondary structure does not involve R group atoms.) The most common types of secondary structures are the A helix and the B pleated sheet. Both structures are held in shape by hydrogen bonds, which form between the carbonyl O of one amino acid and the amino H of another.

The tertiary structure is primarily due to interactions between the R groups of the amino acids that make up the protein.Protein tertiary structures are the result of weak interactions. When a protein folds, either as it is being made on ribosomes or refolded after it is purified, the first step involves the formation of hydrogen bonds within the structure to nucleate secondary structural (alpha and beta) regions.

The quaternary structure proteins are made up of multiple polypeptide chains, often referred to as protein subunits. These subunits may be the same or different. The refers to the quaternary structure how these protein subunits interact with each other and arrange themselves to form a larger aggregate protein complex. The final shape of the protein complex is once again stabilized by various interactions, including hydrogen bonding,