Proteins are among the most abundant organic molecules in living systems and are way more diverse in structure and function than other classes of macromolecules. They contain nitrogen and sulfur. A single cell can contain thousands of proteins, each with a unique function. Although their structures, like their functions, vary greatly, all proteins are made up of one or more chains of amino acids. Types of proteins include enzymes and hormones.
Proteins can play a wide array of roles in a cell or organism.
Protein Types and Functions
| Role | Examples | Functions |
|---|---|---|
| Digestive enzyme | Amylase, lipase, pepsin | Break down nutrients in food into small pieces that can be readily absorbed |
| Transport | Hemoglobin | Carry substances throughout the body in blood or lymph |
| Structure | Actin, tubulin, keratin | Build different structures, like the cytoskeleton |
| Hormone signaling | Insulin, glucagon | Coordinate the activity of different body systems |
| Defense | Antibodies | Protect the body from foreign pathogens |
| Contraction | Myosin | Carry out muscle contraction |
| Storage | Legume storage proteins, egg white (albumin) | Provide food for the early development of the embryo or the seedling |
A protein’s shape is critical to its function, and many different types of chemical bonds may be important in maintaining this shape. Changes in temperature and pH, as well as the presence of certain chemicals, may disrupt a protein’s shape and cause it to lose functionality, a process known as denaturation.