4. Support.
- Fibrous, or threadlike, proteins play structural
roles; these structural proteins include keratin in
hair, fibrin in blood clots, and collagen,
5. Motion.
- Muscles contract through the sliding motion of
two kinds of protein filament: actin and myosin.
6. Contractile proteins
- play key roles in the cell’s cytoskeleton and in
moving materials within cells.
7. Regulation.
-Small proteins called hormones serve as intercellular
messengers in animals.