Cytoskeleton

Definition
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Network of each cell consisting of thin, thread-like protein structures (filaments). The cytoskeleton is responsible for the mechanical stability of a cell as well as for active movements of a cell. It also performs sensory functions that are important for signal transmission between cells.

Classification
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There are 3 classes of cytoskeletal filaments, each of which is formed by different proteins or classes of proteins, each of which has specific accompanying proteins and each of which participates in different ways in the tasks of the cytoskeleton:
- Actin filaments,
- intermediate filaments,
- microtubules.
Actin filaments (also microfilaments) are fibres with a diameter of 7 nm. They are arranged like a net in the cell, stabilize its outer shape and fix membrane-bound proteins in their place. The motor proteins of actin form the protein class of myosins. The movement of the muscles is mainly based on interactions between actin and myosin.
Intermediate filaments: These are a series of protein filaments about 10 nm (8-11 nm) in diameter. They are much more stable than microtubules and actin filaments and absorb mainly mechanical traction forces. Thus, they mainly serve to mechanically stabilize the cells and form their supporting scaffold. 6 Intermediate filaments are distinguished:
- acidic keratins: occurrence in epithelia
- basic keratins: occurrence in epithelia
- Desmine:
  - GFAP (glial fibrillar acidic protein): Occurrence in glial cells, astrocytes
  - desmin (muscle cells)
  - Vimentin (cells of mesenchymal origin)
  - Peripherin (found in peripheral neurons)
- alpha-internexin (found in the CNS during development)
- Laminins:
  - Laminin A, lamin B, lamin C (found in the nucleus)
- Neurofilaments:
  - NF-L, beta-internexin, NF-M, NF-A (found in neurons)
  - Nestin (neuroepithelial stem cells)
Microtubules: hollow cylinders with a diameter of 25 nm. They are composed of the protein tubulin. Intracellularly, with their motor proteins dynein and kinesin, they are responsible for prolonged transport processes and the movement or attachment of organelles in the cytosol.