Cytoskeleton
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Direct answer
The cytoskeleton is an elaborate network of proteinaceous fibres that courses through the cytoplasm of eukaryotic cells, consisting of microtubules, microfilaments and intermediate filaments. It is involved in mechanical support, motility and the maintenance of cell shape: microtubules, made of tubulin, form the spindle and the axonemes of cilia and flagella; microfilaments, made of actin, drive cytoplasmic streaming and cleavage; and intermediate filaments consolidate the structural framework. It is a dynamic structure, being dismantled and rebuilt as the cell's activities change.
What you must remember
- Three components: microtubules (hollow cylinders about 25 nanometres wide), microfilaments (solid, about 7 nanometres) and intermediate filaments (about 10 nanometres, intermediate in size between the two).
- Microtubules: composed of the protein tubulin; form the mitotic spindle that separates chromosomes, and the 9+2 axoneme core of cilia and flagella, plus centrioles and basal bodies.
- Microfilaments: composed of actin; responsible for cytoplasmic streaming (cyclosis), amoeboid movement, and the cleavage furrow of dividing animal cells.
- Intermediate filaments: rope-like fibres without motor activity; anchor organelles and maintain cellular integrity, notably in animal cells.
- Functions summarised: mechanical support to the cell and maintenance of its shape; motility of the whole cell or of cell components; intracellular transport along the fibres.
- Dynamic nature: the fibres polymerise and depolymerise as needed, letting the cell reshape rapidly during division, movement and growth.
Common confusion
The protein identities are swapped more often than anything else here: tubulin builds microtubules and actin builds microfilaments — reversing them is the classic mark-loser. The second confusion is between the cytoskeleton and the cell wall; the wall is a non-living outer secretion giving tissue-level rigidity, whereas the cytoskeleton is a living intracellular network. Note also that intermediate filaments do not participate in movement — they are structural — so any option pairing them with motility is wrong.
Exam-focused takeaway
NEET-UG keeps cytoskeleton questions short and definitional: identify the three fibre types, match tubulin with microtubules and actin with microfilaments, and state the trio of functions (mechanical support, motility, maintenance of shape) that NCERT lists. Link microtubules forward to the spindle apparatus and the 9+2 arrangement of cilia, which the exam treats as cell-biology overlaps. Statement items often assert that intermediate filaments cause movement; be ready to reject that pairing instantly.
Frequently asked questions
What are the three types of cytoskeletal fibres?
Microtubules, microfilaments and intermediate filaments, differing in diameter, protein composition and function.
Which proteins make up microtubules and microfilaments?
Microtubules are polymers of tubulin, while microfilaments are polymers of actin.
What roles does the cytoskeleton play in a cell?
It provides mechanical support, maintains cell shape and participates in motility, including intracellular movement of organelles.
How are microtubules connected to cell division?
Microtubules form the spindle fibres that attach to chromosomes and pull them to opposite poles during mitosis and meiosis.
Do intermediate filaments help in movement?
No, intermediate filaments mainly provide structural support and anchor organelles; movement involves microtubules and microfilaments.