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Cytoskeleton

Lecture IIb

Bismark Oliver C. Lemana, M.Sc. Biological Sciences Department, College of Science University of Santo Tomas, Manila

Complex network of protein structures: Microtubules

Microfilaments (actin filaments)

Intermediate filaments

Functions: Determine cell shape

Movement of organelles and particles in and out of the cell

Movement of the entire cell

Cytoskeleton

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Found in:

Cytoplasm of eukaryotic cells

Cilia and flagella

centrosomes

and tubulin

13 units in a complete spiral

Polymerization controlled by Ca2+ and MAPs

Microtubules

Polymerization of microtubules

Microtubule growth

Occurs at the extremities (+ and ends)

Microtubules

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Microtubule

Polymerization of microtubules Microtubule growth

Occurs at the extremities (+ and ends)

Colchicine Blocks the (+) extremity from adding more tubulin

units

Depolarization at (-) end

Arrests mitosis at metaphase stage

Vincristine, vinblastine and taxol Prevention of cancer cell proliferation

Microtubules

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Cilia and flagella

Movement of materials

Cell locomotion

Microtubules

Microtubules

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Spindle Fibers

Function: Contractile activity (actin and myosin)

Present in muscle tissues

Organization 1. Skeletal muscles

Paracrystalline array integrated with myosin filaments

2. Most cells Formation of cell cortex in plasmalemma

Associated with endo- and exocytosis, and cell migratory activity

Actin Filaments

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3. Association with organelles

Shifting and moving of cytoplasmic components

Cytoplasmic streaming

4. None-muscle myosin

purse-string ring of filaments

Cleavage of mitotic cells

5. Scattered in unorganized fashion in cytoplasm

Actin Filaments

Actin Filaments

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Proteins associated with IF Keratins

Found in epithelia Epidermis, nails, hooves, horns, feathers, scales Protection from abrasion, dehydration and heat

Vimentin Mesenchymal in origin

Desmin (skeletin) Smooth muscles and the Z-disks of skeletal and cardiac muscles

Glial filaments Characteristic of astrocytes

Neurofilaments Restricted to neurons

Lamins Structural network of the nuclear envelop

Intermediate Filaments

10 MINUTE BREAK!!!