Fiberous proteins often serve the same function that cellulose serves in plants.
Most animal tissue is built out of proteins.
Ligaments, tendons, cartilege and hair are all made of protein. In the image to the right are two different kinds of protein fibers. The Blue and yellow fibers are actin and the red fiber is myosine. These proteins together make up muscle tissue. The ability of Myosine fibers to creep along the actin fibers allows muscles to contract.