Intermediate Filaments: Examples and Functions in Human Cells

📚 Quick Study Guide

• 🧬 Definition: Intermediate filaments (IFs) are cytoskeletal protein structures found in the cytoplasm of eukaryotic cells. They provide mechanical support and help maintain cell shape.
• 🔩 Structure: IFs are ~10 nm in diameter, "intermediate" in size between actin filaments and microtubules. They are composed of fibrous subunits coiled together.
• 🛡️ Function: Primarily provide tensile strength to cells and tissues. They anchor organelles and participate in cell-cell and cell-matrix junctions.
• 📍 Location: Found throughout the cytoplasm and also within the nucleus (lamins).
• 🧪 Examples:
  • Keratins (epithelial cells)
  • Vimentin (fibroblasts, leukocytes, endothelial cells)
  • Desmin (muscle cells)
  • Neurofilaments (neurons)
  • Lamins (nuclear envelope)
• 🤝 Assembly: IF assembly does not require nucleotide triphosphate (ATP or GTP) hydrolysis, unlike actin filaments and microtubules.
• 🧫 Regulation: Phosphorylation can regulate IF assembly and disassembly.

Practice Quiz

1. Which of the following is a primary function of intermediate filaments in human cells?
   1. A. Facilitating cell movement
   2. B. Providing tensile strength
   3. C. Transporting organelles
   4. D. Participating in cell signaling
2. Which type of intermediate filament is typically found in epithelial cells?
   1. A. Vimentin
   2. B. Desmin
   3. C. Keratin
   4. D. Neurofilament
3. Where are lamins, a type of intermediate filament, primarily located?
   1. A. Cytoplasm
   2. B. Plasma membrane
   3. C. Nuclear envelope
   4. D. Endoplasmic reticulum
4. Which cell type contains desmin as its primary intermediate filament?
   1. A. Fibroblasts
   2. B. Neurons
   3. C. Muscle cells
   4. D. Epithelial cells
5. What is the approximate diameter of intermediate filaments?
   1. A. 5 nm
   2. B. 7 nm
   3. C. 10 nm
   4. D. 25 nm
6. What distinguishes intermediate filament assembly from actin filament and microtubule assembly?
   1. A. Requires GTP hydrolysis
   2. B. Requires ATP hydrolysis
   3. C. Does not require nucleotide triphosphate hydrolysis
   4. D. Requires calcium ions
7. Which of the following processes can regulate the assembly and disassembly of intermediate filaments?
   1. A. Glycosylation
   2. B. Methylation
   3. C. Phosphorylation
   4. D. Acetylation