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: Concept Summary:
Eukaryotic cells possess a cytoskeleton composed of microfilaments (actin filaments), intermediate filaments, and microtubules. These filaments vary in protein composition, structure, and diameter. This question focuses on the diameter of actin filaments.

Step 2: Detailed Filament Properties:
- Actin Filaments (Microfilaments): The thinnest filaments, polymers of actin, forming flexible, helical structures. Their diameter is approximately 7-8 nm.
- Intermediate Filaments: Intermediate in diameter, composed of various proteins (e.g., keratin, vimentin, lamin), with a diameter of about 10 nm.
- Microtubules: The thickest filaments, hollow tubes of tubulin dimers, with an outer diameter of about 25 nm.

Step 3: Solution:
Given the options are in micrometers and nanometers, and knowing cytoskeletal filaments are on the nanometer scale, we can eliminate the micrometer options. Of the nanometer options, 8 nm is the closest to the actual diameter of an actin filament.
Therefore, option (D) is correct.