The cytoskeleton is the cell's dynamic scaffolding system. It's made up of protein filaments that maintain cell shape, enable movement, and facilitate internal transport. This network is crucial for cell division, ensuring genetic material is evenly distributed to daughter cells.
There are three main types of cytoskeletal filaments: microfilaments, intermediate filaments, and microtubules. Each type has unique properties and functions, working together to support cellular processes and maintain structural integrity.
Structure and Function of the Cytoskeleton
Structure and function of cytoskeleton
- Dynamic network of protein filaments extending throughout eukaryotic cell cytoplasm
- Maintains cell shape by providing mechanical support (skeleton of the cell)
- Enables intracellular transport by serving as tracks for organelle and vesicle movement (highways within the cell)
- Crucial for cell division by forming the mitotic spindle to segregate chromosomes (ensures genetic material is evenly distributed to daughter cells)
- Consists of three main protein filament types
- Microfilaments (actin filaments)
- Intermediate filaments
- Microtubules
Types of cytoskeletal filaments
- Microfilaments (actin filaments)
- Thin, flexible filaments (6-8 nm diameter) composed of actin monomers
- Enable cell movement (muscle contraction), maintain cell shape
- Support plasma membrane, form cellular protrusions (microvilli, lamellipodia)
- Contribute to stress fibers, which provide tension and support cell adhesion
- Intermediate filaments
- 8-12 nm diameter filaments made of keratins, lamins, vimentins
- Provide mechanical strength, resistance to shear stress (help cells withstand external forces)
- Maintain cell shape, anchor organelles within cytoplasm
- Involved in cell-cell and cell-matrix adhesion (desmosomes, hemidesmosomes)
- Microtubules
- Hollow, cylindrical structures (25 nm diameter) of α- and β-tubulin dimers
- Organize cytoplasm, provide tracks for intracellular transport (dynein and kinesin motor proteins move along microtubules)
- Form mitotic spindle during cell division to segregate chromosomes
- Provide structural support for cilia and flagella
- Originate from the centrosome, which acts as the main microtubule-organizing center
Cellular Motility and Cytoskeletal Differences
Cilia and flagella in motility
- Specialized organelles protruding from cell surface enabling movement
- Structure
- Core axoneme of nine doublet microtubules in 9+2 pattern (nine outer doublets around two central singlets)
- Dynein arms connect outer doublets, generate force for movement (ATP-powered motor proteins)
- Basal body anchors cilium/flagellum to cell, organizes microtubule assembly
- Function
- Cilia shorter, more numerous, beat coordinately to move fluids/particles (respiratory tract, fallopian tubes)
- Flagella longer, less numerous, propel cells through liquid (sperm cells)
Cytoskeleton in prokaryotes vs eukaryotes
- Prokaryotic cells
- Lack true cytoskeleton, possess actin (MreB) and tubulin (FtsZ) homologs
- MreB forms helical filament beneath cell membrane, maintains shape, involved in cell wall synthesis
- FtsZ forms Z-ring at division site, guides cell wall synthesis during binary fission
- Eukaryotic cells
- Complex cytoskeleton with microfilaments, intermediate filaments, microtubules
- Animal cells
- Lack cell wall, rely on cytoskeleton for support and shape
- Intermediate filaments provide tensile strength, resist mechanical stress (skin cells, muscle cells)
- Plant cells
- Cell wall provides support and determines shape
- Microtubules crucial for cell wall deposition during growth and division
- Intermediate filaments less abundant and diverse than in animal cells
Cytoskeleton Dynamics and Cell Polarity
- Cytoskeleton undergoes constant remodeling (cytoskeleton dynamics) to respond to cellular needs
- Cell polarity established and maintained through asymmetric organization of cytoskeletal elements
- Focal adhesions connect the cytoskeleton to the extracellular matrix, facilitating cell-substrate interactions