What is a hollow rod composed of tubulin proteins that contributes to the structure of the cytoskeleton?

Microtubules are indeed hollow rods composed of tubulin proteins, which are essential components of the cytoskeleton in eukaryotic cells. They play several critical roles, including providing structural support to the cell, facilitating intracellular transport, and forming the spindle apparatus during cell division. Their dynamic nature allows them to grow and shrink, providing flexibility and enabling the cell to adapt to various conditions.

In contrast, intermediate filaments, while also part of the cytoskeletal network, are more varied in composition and provide mechanical support rather than the hollow structure seen in microtubules. Microfilaments, composed primarily of actin, are involved in cell movement and shape changes but are not hollow. Actin filaments are synonymous with microfilaments and do not form the hollow structures characteristic of microtubules. Therefore, the defining feature of microtubules being hollow rods made of tubulin distinctly qualifies them as the correct answer to this question.