| Category | Function |
|---|
| Enzymes | Catalyze (speed up) biochemical reactions |
| Structural proteins | Provide physical stability and movement |
| Defensive proteins | Recognize and respond to nonself substances (e.g., antibodies) |
| Signaling proteins | Control physiological processes (e.g., hormones) |
| Receptor proteins | Receive and respond to chemical signals |
| Membrane transporters | Regulate passage of substances across cellular membranes |
| Storage proteins | Store amino acids for later use |
| Transport proteins | Bind and carry substances within the organism |
| Gene regulatory proteins | Determine the rate of expression of a gene |
| Motor proteins | Cause movement of structures in the cell |