Question

The approximate diameter of actin filaments is:

• A. 4 micrometer (\(\mu\)m)
• B. 8 micrometer (\(\mu\)m)
• C. 4 nanometer (nm)
• D. 8 nanometer (nm)

Hint:

Remember the relative sizes: Actin Filaments<Intermediate Filaments<Microtubules. A good way to remember the approximate diameters is 7-8 nm (Actin), 10 nm (Intermediate), and 25 nm (Microtubules). Be careful with units: 1 micrometer (\(\mu\)m) = 1000 nanometers (nm).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The cytoskeleton of a eukaryotic cell is composed of three main types of protein filaments: microfilaments (actin filaments), intermediate filaments, and microtubules. These filaments differ in their protein composition, structure, and diameter. The question asks for the diameter of actin filaments.

Step 2: Detailed Explanation:
- Actin Filaments (Microfilaments): These are the thinnest of the three types. They are polymers of the protein actin and form a flexible, helical filament. Their diameter is approximately 7 to 8 nanometers (nm).
- Intermediate Filaments: As their name suggests, their diameter is intermediate between the other two. They are made of various proteins (like keratin, vimentin, lamin) and have a diameter of about 10 nm.
- Microtubules: These are the thickest cytoskeletal filaments. They are hollow tubes made of tubulin protein dimers and have an outer diameter of about 25 nm.

Step 3: Final Answer:
The options provided are in micrometers and nanometers. Micrometers are far too large for a cytoskeletal filament. The correct range is in nanometers. Between the nanometer options, 8 nm is the most accurate approximation for the diameter of an actin filament.
Therefore, option (D) is the correct answer.