Protein make up more than 50% of the dry mass of most cells. It plays major roles in organisms.
| Type of protein | Function | Examples |
|---|---|---|
| Defensive protein | Protect against disease | Antibody |
| Enzymatic protein | Catalyst of chemical reaction | Lactase |
| 存储protein | 存储of amino acids | Casein |
| Transport protein | Transport substance | Hemoglobin |
| Hormonal protein | Coordinate an organism activities | Insulin |
| Receptor protein | Response to chemical stimuli | Receptor in nerve cell membrane |
| Motor protein | Movement | Actin, myosin |
| Structural protein | 支持 | Keratin |