Proteins are linear polymers of amino acids. They fold into compact structures. Sometimes, these folded structures associate to form homo-or hetero-dimers. Which one of the following refers to this associated form?

Some proteins consist of two or more polypeptide chain, called subunits (protomer). The spatial relation of subunits with one another is called the quaternary structure. Dimers contain two polypeptide chains. Homodimers have same polypeptide chains whereas heterodimers have different polypeptide chains.