Which structure consists of two or more polypeptide chains?

The quaternary structure of a protein is characterized by the organization and interaction of two or more polypeptide chains, often referred to as subunits. These chains can be identical or different, and their arrangement and interaction are crucial for the biological function of the protein.

In this structure, the subunits can come together to form a larger, functional protein complex. The assembly of these subunits can involve various types of interactions, such as ionic bonds, hydrogen bonds, hydrophobic interactions, and disulfide bridges, which stabilize the overall structure.

Understanding the quaternary structure is fundamental for comprehending how proteins function in biological systems, as many proteins require multiple polypeptide chains to work effectively. This contrasts with primary, secondary, and tertiary structures, which refer to stages of a protein's configuration that do not yet involve multiple polypeptide chains coming together to assume a complete functional form.