Which type of cytoskeletal filament is characterized by a diameter of approximately 25 nm and is composed of tubulin subunits?

• A. Intermediate filaments
• B. Collagen fibers
• C. Actin filaments (microfilaments)
• D. Microtubules

Answer: (D)

Verified step by step guidance

1. Understand the question: The problem is asking about a cytoskeletal filament with a specific diameter (approximately 25 nm) and composed of tubulin subunits. The cytoskeleton is a network of protein filaments in cells that provides structural support, intracellular transport, and other functions.
2. Review the characteristics of the cytoskeletal filaments: The cytoskeleton is made up of three main types of filaments: microtubules, intermediate filaments, and actin filaments (microfilaments). Each has distinct properties, including size and composition.
3. Recall the properties of microtubules: Microtubules are the largest cytoskeletal filaments, with a diameter of approximately 25 nm. They are composed of tubulin subunits, which polymerize to form hollow tubes. Microtubules are involved in processes such as cell division, intracellular transport, and maintaining cell shape.
4. Eliminate incorrect options: Intermediate filaments have a smaller diameter (about 10 nm) and are composed of various proteins, not tubulin. Collagen fibers are extracellular matrix components, not cytoskeletal filaments. Actin filaments (microfilaments) are the smallest cytoskeletal filaments, with a diameter of about 7 nm, and are composed of actin, not tubulin.
5. Conclude that the correct answer is microtubules, as they match the given characteristics: a diameter of approximately 25 nm and composition of tubulin subunits.