What function do structural proteins serve in a cell?

Structural proteins play a crucial role in providing support and shape to cells. These proteins contribute to the integrity and stability of cellular structures, forming the framework that maintains the cell's shape and architecture. For example, proteins such as collagen in connective tissues and keratin in hair and nails are pivotal in organizing cells and providing physical strength to tissues.

In contrast, the other answer choices describe different functions vital to cellular activities. Some proteins are indeed involved in catalyzing biochemical reactions, acting as enzymes (as mentioned in option A), while others serve as energy sources, like stored proteins that the body can break down as needed (referenced in option C). Additionally, certain proteins play key roles in regulating gene expression, controlling when and how genes are turned on or off (which relates to option D). Однако, none of these functions pertain to the specific role that structural proteins serve, which is primarily to maintain the physical architecture of cells.