Which cytoskeletal element serves as tracks for intracellular transport and is the substrate for dynein and kinesin?

• A. Microfilaments
• B. Nuclear lamina
• C. Intermediate filaments
• D. Microtubules

Answer: (D)

Intracellular transport uses highways formed by microtubules. These hollow tubes, built from tubulin dimers, provide directional tracks for motor proteins like dynein and kinesin. Dynein typically moves cargo toward the minus end of microtubules (usually toward the cell center), while kinesin carries cargo toward the plus end (toward the cell periphery). Because these motors travel along microtubules, they depend on this cytoskeletal network to move vesicles and organelles efficiently within the cell. Other cytoskeletal elements have different roles—actin filaments support cortical structure and muscle contraction, intermediate filaments give mechanical stability, and the nuclear lamina sits inside the nuclear envelope rather than in the cytoplasm.