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CYTOSKELETON II Intermediate Filaments Prof. Dr. Müjgan CENGİZ Intermediate Filaments 1. Their diameter about 10 nm(actin 7,microtubul 25 nm) 2. All eukaryotic cells contain actin and tubulin 3. They Found only at metazoans (vertebrates, nematodes, mollusca). 4-They are not involved in cell movement. They play structural role by provide mechanical stres. They have rope like character. They can easily bent but difficult to break. Actins and microtubuls polymers of single type proteins, İntermediate filaments different types of proteins. Major function is to supply physical strength to the cells and tissues. Plentiful in neronal aksons. There are more than 50 different Int. Filament. They are identified and classified into six groups . Classification based on similarities of their amino acids. There are 2 types of keratins(they are used for production of hair nails and corns). Acidic keratins(type I), basic/neutral keratins(type II). 20 different types of human epitel cells exist 10 type more specific for hair and nails. Some types of type I and II keratins called (hard keratins)(hair, nail and corn) The types of type I and II keratins called(soft keratins) Abundant in epthelial cells. The type III IF include vimentin. Type IV NF include 3 type of proteins(L;H;M).Major NF of mature neurons ɑ internexin expressed early stage of neuron development Cooper,G.M: The Cell. A molecular Approach 2nd edition. Boston university. Sunderland(MA). Sinauer Associates,2000 L Cross linked keratin networks held together with S-S bond. They may survive even after death of the cells. Disease about keratin Epidermolysis bullosa simplex (mutation in keratinType 14). (defective keratins expressed in the basal layer of the epidermis). ALS (amylotropic lateral sclerosis. Loss of motor neurons) Microtubules 1. Microtubules are polymers of protein tubulin 2. Tubulin is a dimer made up of two closely related a and b tubulin. 55kd 3. Dimers aggregate head to tail to form parallel arrays of protofilaments. 4. Microtubules consist of 13 linear protofilaments assembled around a hollow core Function of Microtubules 1. Cell shape 2. Self locomotion 3. Intracellular transport of organelles 4. Separation of chromosomes during mitosis Polarity of Microtubules 1. Microtubules like actin filaments are polar structures with two distinct ends, fast growing and slow growing. 2. Polarity is important consideration in determining the direction of movement along microtubules just like the polarity of actin filament, which defines the direction of myosin movement. Stabilization of Microtubules and cell polarity Dynamic behaviour of the microtubules is regulated by 1-Ca Low con of the Ca increases polymerization(1.10-6) 2-MAPs –Microtubul associated proteins. Map1, Map2, Map3, Map4(bins the microtubuls and inhibit dis.of tubulin) 3-Tau proteins. Only one Tau gene 64 different tau protein) Drugs which bind tubulin: Colchicine Colcemid Vincristine Vinblastine Inhibit polymerization And thus selectively inhibit Cell division Taxol Stabilizes microtubules and also Blocks cell division Anti-Cancer Drugs Vinblastine and vincristine bind tubulin and inhibit polymerization. They inhibit selectively rapidly dividing cells. Taxol stabilizes microtubules rather than inhibiting their assembly. Such stabilization blocks cell division Amantia falloides is a mushroom and falloidin isolated from it. It binds to the aktin and increazes its polymerization. Motor Proteins in Cytoskeleton 1. Myosin - Translocates along actin toward positive ends 2. Kinesin - Translocates along microtubules toward positive ends 3. Dynein - Translocates along microtubules toward negative ends Properties of Dynein • 2000 kd protein • 2 or 3 heavy chains with a number of light chain and intermediate polypeptides. • Globular head domains are motor domains which bind ATP • Dynein occurs in several forms but all move along microtubules toward minus ends Properties of Kinesin • Kinesin head (340 AA) and myosin head (850 AA) domains are structurally similar. From the common ancestor. • This portion is responsible for binding to other cell component. • 100 other kinesin proteins have known. • Some move along microtubules toward the positive and some towards the negative ends. • Different tail sequences - move different cargo types - vesicles, organelles and chromosomes. • CENTROSOME • Centrosome is the microtubule organizing(MOC) center in which the minus ends of microtubules are anchored. It is located adjacent to the nucleus near the center of the interphase cells. • Centrosome plays a big role in determining the intracellular organization of microtubules. • Centrosome serves as the initiation role of the assembly of microtubules which grow outward from the centrosome toward the periphery of the cell. Organization of Microtubules in Nerve Cells • A neuron has a cell body, an axon and dendrites • Axons and dendrites contain microtubules in certain polarity • Both contain specific MAP proteins • Axons contain tau protein and no MAP-2 • Dendrites contain MAP-2 and no tau •Microtubule associated proteins (MAP) bind to microtubules and increase their stability •There are alot of of MAPs have been identified. Most well known are, MAP-1, MAP-2 and tau and MAP-4 in nonneuronal cells. •The tau protein is the main component which found in the brains of Alzheimer patients.