MICROTUBULE CONSTRUCTION a. Dimerization of a and b tubulin subtypes

b. Linear repitition of the heterodimers makes a MOUVEMENT -Centriole a b - a b - a b - a b - a b - a b - a b - a b - a b - a b + Microtubule organizing tubulin protofilament growing -Centrosome center -Kinetochore c. Side-by-side assembly of 13 protofilaments to make a sheet -Axonène d. Rolling of the sheet into a tubule

-Cellule ciliée + e. Elongation controlled by [ions] [a b ] GTP GDP rate

Colchicine blocks elongation

BUILD A CENTRIOLE or BASAL BODY

Assemble 2 partial & one CENTRIOLES - MTOC - complete microtubules into KINETOCHORES a TRIPLET C 10 B subfibers 10 13 A protofilaments

Arrange 9 triplets in parallel & position an identical array nearby & perpendicular

CENTROSOME = 2 Centrioles + Microtubule Organizing Center

1 • The cell cycle and mitosis: mechanism (example)

nonkinetochore kinetochore microtubule microtubules

MICROTUBULES BUILD AN AXONEME of or flagellum The axoneme has a 9 double MT + 2 center MT pattern with dynein arms on the outside for sliding action! Extend A & B subfibers to be the axoneme’s doublets This is the “Sliding Filament Theory”

B 10 subfibers 13 protofilaments A

9 doublets

central pair

Other microtubule arrays are the MITOTIC SPINDLE & AXONAL CORE

2 MICROTUBULES FOR THE CILIARY BEAT

Dynein arm with ATPase activity to power movement - generating a sliding interaction with B subfiber of adjacent microtubule doublet

Connections turn the microtubule sliding into BENDING of the Cilium

3 MICROTUBULES FOR THE CILIARY BEAT CILIATED AIRWAY CELL

Dynein arm with ATPase 9 + 2 Microtubular array (9 doublets) activity to power movement - CILIUM generating a sliding interaction Basal bodies with 9 + 0 array (9 triplets) with B subfiber of adjacent . . Zonula occludens microtubule doublet . Zonula adherens

Macula adherens/ Connections turn the microtubule GOLGI Keratin Intermediate Filaments sliding into BENDING of the Cilium

Centrioles & MTOC MEDICAL CORRELATIONS for Microtubules A genetic axonemal dynein deficiency impairs ciliary clearance of luminal the airway, leading to severe lung infections of Kartegener’s cortex syndrome lateral Hemi-desmosome

Dangerous cell proliferation in cancer can be halted by vinblastine . which blocks mitotic spindle formation BL basal

SENSORY ON AUDITORY SENSORY STEREOCILIA ON AUDITORY HAIR CELL

bundled, as the as the core of the stereocilium Stereocilia are core of the stereocilium non-motile, Actin filaments Ion channels Actin filaments opened by but can be deflection of meshwork, as anchoring moved by the meshwork stereocilium cuticular plate stimulus Stereocilia are non-motile, Hair cell also but can be has a solitary moved by the tall true stimulus cilium, with microtubules

Synapses

4 SENSORY STEREOCILIA ON AUDITORY HAIR CELL

bundled, as the as the core of the stereocilium Actin filaments meshwork Note: no Ion channels microtubules in the signal-transduction mechanism

& Stereocilia are non-motile

So why the ‘cilium’ name? Why, indeed!

Synapses

Dynein arms move across adjacent MTs and cause sliding and axonemal bendingmotion

5 CELL SHAPES VARIETIES OF MOVEMENT

1 Cylindrical/columnar, cuboidal, polyhedral, flattened Ciliary & Flagellar Whole cell epithelial cell shapes to fit into multicellular patterns Intracellular vesicles Extension of processes 2 Spheroid & Ovoid - defensive blood cells Chromatids during mitosis Separation of cells at mitosis 3 Elongated - muscle cells & fibroblasts Whole cell (sperm) Intracellular vesicles 4 Multiple branching processes - neurons, glial cells, pigment cells by MICROTUBULES by ACTIN FILAMENTS Generalizations Generalization Little direct motor role for Intermediate Filaments Microtubules and intermediate filaments with cell junctions Microtubules & IFs highly concentrated around the nucleus & hold shape and polarization extend radially; actin more peripheral under the plasmalemma in the “cortex” Exceptions are: muscle, neurons, mature epidermal cells, RBCs Actin microfilaments (with & without ) modify shape Movements are closely related to cell’s shape & polarity

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