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#cell movement

6 public questions tagged with this topic.

Basics of Cell Biology

Which of the following is not a function of the cytoskeleton?

Cytoskeletal networks coordinate shape, division, and intracellular logistics. Actin filaments, 7 nm flexible helical polymers of ATP-G-actin nucleated by Arp2/3 at 70 degree branch and formins for linear cables, interact with 50 myosin classes for cortical contraction, formation of contractile ring with myosin II during cytokinesis, lamellipodial protrusion, and vesicle movement near periphery. Microtubules, 25 nm rigid hollow tubes of alpha-beta tubulin heterodimers assembling head to tail with GTP cap regulating dynamic instability, serve as polarized tracks for kinesin families moving outward to plus ends and dynein moving inward, positioning Golgi, endosomes, mitochondria, and assembling mitotic spindle with kinetochore capture ensuring chromosome segregation. Intermediate filaments, 10 nm non-polar rope-like polymers keratin, vimentin, desmin, lamins anchored via plectin and nesprin, provide mechanical resilience against shear stress. Together they govern intracellular transport, mechanical support, and motility. Protein synthesis uses ribosomal peptidyl transferase in cytoplasm and rough ER, not filaments, so translation is not cytoskeletal function.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Cytoskeleton Functions Overview.

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Cytoskeleton

Which type of myosin is primarily involved in non-muscle cell contractility?

Non muscle contractility underpins stress fiber maintenance, adhesion maturation, morphogenesis and wound closure, distinct from skeletal muscle sarcomeres employing troponin regulation. Myosin II family in non muscle cells includes isoforms IIA, IIB and IIC sharing hexameric composition two heavy chains plus essential and regulatory light chains, forming short bipolar filaments that transiently associate with actin rather than stable thick filaments. Activation occurs via phosphorylation of 20 kilodalton regulatory light chain RLC at Ser19 by calcium calmodulin dependent MLCK and Rho associated kinase ROCK, converting autoinhibited 10S folded conformation to extended 6S assembly competent state enhancing actin activated ATPase. Coordinated pulling of antiparallel actin bundles generates isometric tension, retrograde flow and cortex stiffness. Isoform IIA drives rapid adhesion turnover at leading edge, IIB sustains prolonged tension at rear. Myosin I single headed tension sensor, myosin III adaptation in photoreceptors, myosin VI minus end directed for endocytosis, not primary contractile generator. Therefore myosin II remains central for non muscle contractility.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 18: Nonmuscle Myosin II in Contractility.

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General Biology of Protists

Cilia and flagella differ mainly in

Cilia and flagella share fundamentally identical internal architecture termed axoneme composed of nine peripheral microtubule doublets surrounding two central singlets, 9+2 arrangement, radial spokes, and dynein motor arms producing bending via ATP hydrolysis and basal body anchoring. Ultrastructurally and proteomically they are synonymous organelles using tubulin and intraflagellar transport. Distinction rests on length, quantity, and waveform: flagella typically longer, fewer, propelling with undulating waves, while cilia are shorter, numerous, beating coordinately in metachronal waves to move fluids or cells, not internal microtubule composition.

Ref: Campbell Biology 11th ed., Chapter 6 Cilia flagella length number waveform same ultrastructure; Cooper Cell Biology 9+2 axoneme

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General Biology of Protists

Amoeboid locomotion occurs through

Amoeboid locomotion relies on dynamic remodeling of actin cytoskeleton producing cytoplasmic extensions termed pseudopodia meaning false feet. Through polymerization of G-actin at leading edge forming lamellipodia and depolymerization at rear, cytoplasm streams inside projection, adhesion complexes anchor to substratum via transmembrane proteins, propelling cell forward. Small GTPases Rac and Cdc42 regulate branching. Forms include lobopodia in Amoeba, filopodia in foraminifera, and reticulopodia in radiolarians. This crawling mechanism also mediates phagocytic capture of bacteria, distinguishing amoeboid motility from swimming via cilia or flagella requiring microtubules.

Ref: Alberts Molecular Biology Cell amoeboid locomotion pseudopodia actin; Campbell Biology 11th ed., Chapter 28 Protist motility pseudopods organization

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Cell Communication and ECM

ECM degradation during cell migration is mediated by

Matrix metalloproteinases, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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