ABSTRACT
In Chapter 1, we saw that protein structure can be subdivided into primary, secondary, tertiary, and quaternary structures. However, evolution does not work in such terms: the fundamental evolutionary unit is the domain. Domains also form the fundamental functional units. This chapter considers why domains are so important. We shall see that they are a convenient size for evolution to make use of, and they provide an instant benefit, allowing evolution to create new proteins and new functions at a stroke.
