51 public questions tagged with this topic.
Microtubules form tracks along which organelles and vesicles move within the ll, facilitating intracellular transport. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Cell Structure and Function, Cell Cycle and Biomolecules, Topic: Cell organelles and biomolecular structure.
P-granules, ribonucleoprotein assemblies marking germline, segregate to posterior blastomere P1 during first division and subsequently to germline precursors P2-P4. Their posterior migration along cell cortex before division requires microtubule motor dynein transporting granule components along cortical microtubules toward centrosome at posterior pole. PAR-1 dependent microtubule organization creates flow. Mutants in dynein heavy chain dhc-1 or its regulator dynactin cause equal distribution of P-granules to both AB and P1, losing germline restriction. Myosin II and kinesin contribute to cort
Ref: Updike & Strome 2010; Gilbert Chapter 4: Dynein motor responsible for P-granule migration in early embryo.
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 outw
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Cytoskeleton Functions Overview.
Cytoskeleton provides scaffold and track system built from protein polymers regulated by nucleation factors, GTPases, and post-translational modifications. Actin filaments, 7 nanometer diameter polarized structures polymerizing from ATP-G-actin mediated by Arp2/3 complex branching at 70 degrees and formins nucleating straight cables for filopodia, associate with myosin II for contractility at cortex and myosin V for short-range vesicle transport near cell periphery, driving lamellipodia extension and endocytic invagination. Microtubules, 25 nanometer hollow tubes of alpha-beta tubulin dimers w
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Cytoskeleton and Intracellular Transport.
Maintenance of biconcave disc shape maximizing surface to volume ratio for deformability and gas exchange depends on membrane skeleton elasticity and organization. Spectrin consists of alpha two hundred eighty kilodalton and beta two hundred forty six kilodalton subunits each containing twenty triple-helical spectrin repeats of one hundred six residues forming elongated flexible anti-parallel heterodimer one hundred nanometers long, two heterodimers associate head to head via helical bundle forming tetramer about two hundred nanometers acting as entropic spring with persistence length about te
Ref: Lux and Palek, Erythrocyte Membrane Skeleton and Spectrin Elasticity, Blood Cells.
Erythrocyte mechanical stability depends on vertical linkages mediated by ankyrin-R isoform one hundred ninety kilodaltons to two hundred ten kilodaltons comprising three distinct domains enabling integration. N-terminal membrane binding domain contains twenty four tandem ankyrin repeats each thirty three residues forming elongated superhelical solenoid that creates concave binding surface recognizing cytoplasmic loop of Band 3 anion exchanger between residues one hundred seventy five to one hundred eighty five with nanomolar affinity, also binding Na K ATPase alpha subunit, voltage gated sodi
Ref: Mohandas and Peters, Erythrocyte Cytoskeleton and Ankyrin Function, Annu Rev Med.
Intermediate filaments constitute one of three major cytoskeletal polymers alongside actin microfilaments and microtubules, classified by ten nanometer diameter and apolar rope-like assembly through parallel coiled-coil dimers antiparallel tetramers laterally associating into filaments without polarity. Major classes include keratins in epithelia, vimentin in mesenchyme, desmin in muscle, glial fibrillary acidic protein in astrocytes, neurofilaments in neurons, lamins in nucleus. Their primary mechanical role is tensile resistance to shear and stretching, absorbing deformation through flexible
Ref: Herrmann J Cell Sci; IF 10nm tensile strength, anchored at desmosomes hemidesmosomes, no polarity.
Dynein heavy chains are among the largest AAA+ machines, containing six concatenated AAA modules forming an asymmetric ring. AAA1 is primary catalytic site where ATP binding closes interface with AAA2, straightening linker and detaching stalk from microtubule. Hydrolysis and phosphate release trigger linker swing from pre to post power stroke, pulling tail forward while microtubule-binding domain reattaches downstream. This cycle strictly depends on ATP concentration and hydrolysis; nonhydrolyzable analogs such as AMP-PNP arrest motility in strong binding state, vanadate traps ADP-Pi intermedi
Ref: Alberts Ch 16 Motor proteins; dynein AAA+ requires ATP hydrolysis, minus-end directed transport.
Cytoplasmic dynein generates minus-end directed transport using a microtubule-binding domain at the tip of an antiparallel coiled-coil stalk that extends from the AAA ring. The binding interface undergoes ATP-dependent registry shift between strong and weak states. When mutations, deletion or antibody blockade abolishes microtubule attachment, the motor continues to bind ATP and hydrolyze it via AAA1, but force cannot be transmitted to the filament, uncoupling ATPase activity from movement. Cargo adaptors such as BICD2, HOOK and dynactin still recruit dynein via tail and intermediate chains, b
Ref: Vale 2003 Cell; Roberts Cell 2013 dynein stalk MTBD binding essential for cargo translocation.
Plectin is a giant cytolinker of the plakin family that simultaneously recognizes actin, microtubules and intermediate filaments, integrating cytoskeletal networks into a cohesive mechanical continuum. Its structure includes an N-terminal actin-binding domain composed of two calponin-homology motifs, a central 200-nm coiled-coil rod dimerization domain, and a C-terminal repeat domain that binds vimentin, keratin, desmin and glial fibrillary acidic protein with distinct isoform specificity. Alternative splicing of first exons targets isoforms to hemidesmosomes via integrin beta4, to focal adhes
Ref: Alberts Ch 16; Fuchs & Cleveland, Science 1998 plakin plectin crosslinks IF, actin, microtubules.
Intermediate filaments are apolar polymers of tetrameric coiled-coil dimers that lack intrinsic nucleotide turnover, so dynamic regulation relies on post-translational modification. Phosphorylation within the N-terminal head domain by mitotic kinases such as Cdk1, Plk1, Aurora B, as well as PKA, PKC and MAP kinases, introduces dense negative charge that disrupts head-to-rod electrostatic interactions essential for filament elongation. The result shifts equilibrium toward soluble tetramers and monomers, enabling mitotic disassembly of vimentin networks and nuclear lamina breakdown at prometapha
Ref: Alberts Ch 16 Cytoskeleton; Lodish Ch 18; IF phosphorylation controls disassembly via head domain serine.
Cilia and flagella motility requires active sliding filament machine within conserved axoneme evolutionary ancient. Structure nine outer doublet microtubules surrounding central pair retains dynein motors as exclusive driver of beating: outer dynein arms contain two or three heavy chains per arm inner arms more heterogeneous but also axonemal dynein isoforms both anchored to A tubule via docking complex and reaching to B tubule of neighboring doublet executing ATP hydrolysis cycle. Power stroke toward minus end attempts to slide doublets relative each other but nexin dynein regulatory complex
Ref: King, J Cell Sci 2012 – Dynein motor protein moves cilia and flagella beating machinery.
