Cytoskeleton
The cytoskeleton is a dynamic network of protein filaments and tubules that extends throughout the cytoplasm of eukaryotic cells, providing structural support, shape, and mechanical resistance. It consists of three main components: microfilaments (actin), intermediate filaments, and microtubules, each with distinct diameters and functions. The cytoskeleton also facilitates intracellular transport, cell division, and cell motility through the action of associated motor proteins such as myosin, kinesin, and dynein.
Comparison of Cytoskeletal Components
| Component | Diameter | Protein Subunit | Primary Function | Motor Protein |
|---|---|---|---|---|
| Microfilaments | 7 nm | Actin (G-actin) | Cell shape, movement, division | Myosin |
| Intermediate filaments | 8–12 nm | Vimentin, keratin, etc. | Mechanical support, anchoring | None |
| Microtubules | 25 nm | Tubulin (α and β) | Intracellular transport, mitosis | Kinesin, Dynein |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Cell Junction
Cell junctions are specialized regions of contact between adjacent cells or between cells and the extracellular matrix, serving roles in structural integrity, intercellular communication, and selective barrier function. In animal tissues, the three major types are tight junctions (which form impermeable seals between epithelial cells), anchoring junctions (desmosomes and hemidesmosomes, which provide mechanical strength), and gap junctions (which form channels allowing direct cytoplasmic communication between cells). Plant cells use plasmodesmata as their equivalent of gap junctions, enabling movement of water, nutrients, and signaling molecules between cells through the cell wall.
Active Transport
Active transport is the movement of molecules or ions across a cell membrane against their concentration gradient (from low to high concentration), requiring the expenditure of cellular energy in the form of ATP. Primary active transport uses ATP directly to power transport proteins called pumps, while secondary active transport uses the electrochemical gradient established by primary active transport to drive the movement of another solute. Active transport is essential for maintaining cellular ion balances, nutrient uptake, and nerve impulse transmission.
Endocytosis
Endocytosis is the process by which a cell engulfs extracellular material by invaginating its plasma membrane to form an intracellular vesicle, allowing large molecules, particles, or even other cells to be taken up without crossing the membrane directly. The three main types are phagocytosis (engulfment of solid particles), pinocytosis (engulfment of fluids and dissolved solutes), and receptor-mediated endocytosis (selective uptake via surface receptors such as clathrin-coated pits). Endocytosis requires energy (ATP) and plays critical roles in immune defense, nutrient uptake, and signal regulation.
From Greek "kytos" (hollow vessel, cell) and "skeletos" (dried body, skeleton). The concept of an intracellular scaffold was developed throughout the 20th century, with the term gaining prominence after electron microscopy techniques revealed the filament network in the 1960s–1970s.