Complex sentence: Microtubules are part of a structural network (the cytoskeleton) within the cell's cytoplasm, but, in addition to structural support, microtubules take part in many other processes.
Split into simpler sentences: Microtubules are part of a structural network (the cytoskeleton) within the cell's cytoplasm. However, in addition to structural support, microtubules also take part in many other processes.