Structural protein

Structural proteins Structural proteins confer stiffness and rigidity to otherwise-fluid biological components. Most structural proteins are fibrous proteins; for example, collagenand elastinare critical components of connective tissuesuch as cartilage, and keratinis found in hard or filamentous structures such as hair, nails, feathers, hooves, and some animal shells. [ 36 ]Some globular proteinscan also play structural functions, for example, actinand tubulinare globular and soluble as monomers, but polymerizeto form long, stiff fibers that make up the cytoskeleton, which allows the cell to maintain its shape and size. Other proteins that serve structural functions are motor proteinssuch as myosin, kinesin, and dynein, which are capable of generating mechanical forces. These proteins are crucial for cellular motilityof single celled organisms and the spermof many multicellular organisms which reproduce sexually. They also generate the forces exerted by contracting muscles [ 37 ]and play essential roles in intracellular transport.