In a trimer we have three subunits. In a tetrimer we have four subunits and so forth. Now, these subunits can be different or they can be identical. It really depends on the type of protein that we're discussing. Now, all the different types of proteins inside our body can usually be categorized into two categories. So we have a type of protein known as a fibrous protein also called structural proteins and we also have globular protein.