The cytoskeleton is composed of three primary components:
Microfilaments
Intermediate Filaments
Microtubules
Each component has unique structural and functional attributes.
Microfilaments
Also Known As: Actin
Size: Smallest of the cytoskeletal elements
Structure:
Made of G-actin monomers
G-actin polymerizes to form F-actin
Two F-actin form a double helix structure
Functions:
Cell Shape and Movement
Allows cells to change shape and move, e.g., diapedesis in white blood cells
Involved in cell division during cytokinesis by forming a constriction ring
Cell Extensions
Forms microvilli (small extensions) and stereocilia (larger extensions)
Microvilli increase surface area for digestion and absorption in the GIT
Stereocilia involved in balance and hearing (inner ear)
Cell Junctions
Integral in tight junctions and adherens junctions, preventing cell separation
Muscle Contraction
Works with myosin for muscle contraction
Membrane Transport
Involved in endocytosis and exocytosis
Intermediate Filaments
Size: Intermediate (middle child)
Characteristics:
Most resilient and tough
Used as immunohistochemical markers in tumor diagnosis
Types and Locations:
Lamins: Found in the nucleus
Keratin: Found in epithelial cells
Vimentin: Found in connective tissue (fibroblasts)
Desmin: Found in muscle cells
Neurofilaments: Found in neurons
Functions:
Cell Structure and Support
Maintains cell shape against compressive forces
Cell Junctions
Forms desmosomes (cell-cell) and hemidesmosomes (cell-extracellular matrix)
Microtubules
Size: Largest of the cytoskeletal elements
Structure:
Composed of alpha and beta tubulin dimers
Forms protofilaments which combine to make a hollow tube
Have polarized ends: positive (periphery) and negative (nucleus)
Functions:
Intracellular Transport
Acts as railroad tracks for motor proteins (kinesin and dynein)
Axonal Transport
Kinesin: Anterograde transport (body to axon terminal)
Dynein: Retrograde transport (axon terminal to body)
Cell Movement
Forms structures like flagella and cilia
Flagella provide motility (e.g., sperm)
Cilia move mucus in the respiratory tract and aid egg movement in Fallopian tubes
Cell Division
Forms centrosomes that give off mitotic spindles
Mitotic spindles connect to chromosomes at kinetochores to separate chromatids
Conclusion
The cytoskeleton is essential for maintaining cell shape, facilitating movement, aiding in cell division, and supporting various other cellular functions.