depending on their tertiary structure, proteins can be classified into 3 categories:
1) fibrous proteins: large, elongated, stiff molecules often composed of tandem copies of a short sequence that forms a single repeating secondary structure (ex: collagen); usually play a structural role or help with movement
2) globular proteins: water-soluble, compactly folded structures, often spherical that comprise a mixture of secondary structures
3) integral membrane proteins: embeded within phospholipid bilayer of cell membranes
these aren't mutually exclusive!