Which type of protein structure is characterized by several protein subunits functioning as one complex?

The type of protein structure characterized by several protein subunits functioning as one complex is known as the quaternary structure. This level of protein organization occurs when multiple polypeptide chains, or subunits, come together to form a single functional protein complex. Each subunit can be identical or different, and they interact through various bonds and interactions, such as hydrogen bonds, ionic bonds, and hydrophobic interactions.

Quaternary structure is crucial for the proper functioning of many proteins, as the interactions between subunits can affect the overall shape and activity of the protein complex. A classic example of a protein with quaternary structure is hemoglobin, which consists of four subunits that work together to transport oxygen in the blood.

The other structures mentioned, such as primary, secondary, and tertiary, refer to different aspects of protein structure. Primary structure refers to the linear sequence of amino acids in a polypeptide chain, secondary structure involves localized folding of the polypeptide into structures like alpha helices and beta sheets, and tertiary structure refers to the overall three-dimensional shape of a single polypeptide chain. Thus, while all these structures are important in defining the structure of proteins, it is the quaternary structure specifically that describes the assembly and