Final answer:
Proteins such as keratin, collagen, and tubulin are exclusively structural and are not involved in cell shape changes. Keratin strengthens hair, skin, and nails, collagen forms connective tissues, and tubulin is part of the cellular scaffold. Actin, myosin, and kinesin, on the other hand, are involved in cell motility and not exclusively structural.
Step-by-step explanation:
To answer the question regarding proteins that are exclusively structural and not involved in cell shape changes, we must look at the role these proteins play within the cell and body. Among the list provided, the proteins known for their primary structural functions are keratin, collagen, and tubulin. Here's why:
- Keratin is a type of protein that provides structural strength to hair, skin, and nails.
- Collagen is the main component of connective tissues, providing support and structure to skin, tendons, and bone.
- Tubulin makes up the microtubules which serve as the scaffold for cells and are involved in a variety of cellular processes, but it is not primarily associated with cell shape changes; rather, it provides a structural framework within cells.
While actin and myosin are contractile proteins that are involved in muscle contraction and cell motility, and kinesin is a motor protein associated with movement along microtubules, these are not considered exclusively structural. Instead, they are linked to movements either of the cells themselves, as in the case of actin and myosin in muscle fibers or of cellular components, as in the case of kinesin. Therefore, the correct selections from the list are keratin, collagen, and tubulin.