Question

Microfilaments are composed of a protein called

• A. Tubulin
• B. Actin
• C. Myosin
• D. Ribosome

Hint:

Keep the cytoskeleton subunits clear:
- Microfilaments = Actin ($7\,\text{nm}$)
- Microtubules = Tubulin ($25\,\text{nm}$)
- Intermediate Filaments = Keratin, Vimentin, etc. ($10\,\text{nm}$)

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The cytoskeleton is a dynamic network of protein filaments in the cytoplasm of eukaryotic cells.
It consists of three primary types of fibers: microtubules, intermediate filaments, and microfilaments.

Step 2: Detailed Explanation:
Microfilaments, also known as actin filaments, are the thinnest components of the cytoskeleton, measuring approximately $7\,\text{nm}$ in diameter.
They are composed of repeating globular monomers of the protein actin (G-actin).
These monomers polymerize in a head-to-tail manner to form two intertwined helical strands of filamentous actin (F-actin).
Let us review the other proteins:
- Tubulin: This dimeric protein polymerizes to form microtubules, which are larger, hollow cylinders ($25\,\text{nm}$ in diameter).
- Myosin: This is a motor protein that interacts with actin filaments to facilitate muscle contraction and cell motility, but is not the structural subunit of the microfilament itself.
- Ribosome: This is a cellular organelle involved in protein translation, not a cytoskeletal protein.

Step 3: Final Answer:
Therefore, microfilaments are composed of actin, which corresponds to option (B).