Cell biology: The protein subunits that assemble to form microtubule walls in eukaryotic cells are known as what?

Introduction / Context:
Microtubules are cytoskeletal polymers that drive chromosome segregation, intracellular transport, and cell shape. Knowing their molecular building blocks is essential for understanding mitosis, vesicle trafficking, and cilia or flagella function.

Given Data / Assumptions:

• Microtubules are hollow cylinders composed of protofilaments.
• Each protofilament is a linear polymer of tubulin heterodimers.

Concept / Approach:
Microtubules polymerize from alpha tubulin and beta tubulin dimers. These assemble head to tail into protofilaments, which associate laterally to form the microtubule wall. Dynamic instability arises from GTP binding and hydrolysis on beta tubulin.

Step-by-Step Solution:

Verification / Alternative check:
Cell biology references consistently identify alpha beta tubulin as the microtubule subunit, distinct from actin based microfilaments and keratin based intermediate filaments.

Why Other Options Are Wrong:

• Actin: microfilaments, not microtubules.
• Pectin and hydroxyproline proteins: components of plant cell walls, not cytoskeletal tubules.
• Keratin: intermediate filaments in animals.

Common Pitfalls:
Mixing up the three filament systems or assuming all filamentous proteins are interchangeable.

Final Answer:
Tubulin