[1] Lectures 7-10 Flashcards
(83 cards)
3 types of cytoskeleton components:
Microfilament [7nm]
Intermediate filaments[8-10nm]
Microtubules [25nm]
Characteristics of actin monomers and filaments:
Monomers= G-actin [globular]
Long chains= F-actin[filamentous]
3 major varieties: alpha, beta, and gamma
Actin monomers (G actin)
Each actin monomer has a binding site for ATP-binds tightly to G actin.
2 monomers can bind tightly w/ 2 other actin monomers to form filamentous actin [f-actin]
Actin monomers are oriented in same or opposite direction?
SAME
Can actin polymerization be reversed?
Reversible….very dynamic!
First step in actin polymerization:
Nucleation: a trimer is formed and additional actin monomers can then be added to either end.
ATP-actin asso. W/ plus [barbed] end and the ATP is hydrolyzed to ADP following polymerization
What determines rate of polymerization in actin:
Proportional to the cytosolic [ ] of actin monomers.
+ ends grow larger at lower [ ] and higher [ ] of monomers indicates growth…low [ ] indicates depolymerization (from - end)
Treadmilling
The intermediate [ ] favor a dynamic equilibrium btw - and + end of actin microfilaments
Drugs that affect polymerization of actin microfilaments:
Cytochalasins: bind to barbed end [blocks polymerization/inhibits cell movement]
Phalloidin: Binds to actin filaments and prevents dissociation. Visualization w/ fluouro.
Drugs that affect treadmilling actin microfilaments
Thymosin:prevents poly. Profilin:regulates poly. +/- Gelsolin: prevent poly/loss Cofilin:trigger depoly. Arp2/3: initiates growth Phalloidin:prevents depoly. Latrunculins:induces depoly.
Spectrin
Actin binding protein Found in RBCs
Binds cortical cytoskeleton to the plasma membrane
Dystrophin
Actin binding protein
Binds to cortical cytoskeleton to plasma membrane
Villin and fimbrin
Actin binding protein
Cross links into microvilli
Calmodulin and myosin I
Actin binding protein
Cross links actin to plasma membrane in microvilli
Alpha-actin
Actin binding protein
Cross links stress fibers and connects actin to protein plasma membrane complex complexes
Filamin
Actin binding protein
Cross links actin at wide angles to form screen like gels…creates networks
Basic structure and assembly of intermediate filaments:
1: 2 monomers form parallel dimer
2: 2 dimers in anti-parallel form tetramer.
3: tetramers align end to end =protofilament
4: pairs of protofilaments asso. Laterally to form protofibril
5: 4 protofibrils wind up to form a rope like 10 nm IF.
NONPOLAR
Type I Intermediate filament ex:
Keratin
Struture of microtubule
25 micrometers diameter
Composed of Tubulin dimers [alpha+beta unit]
Protofilaments in longitudinal rows of tubulin dimers
13 protofilaments in PARALLEL - cylindrical w/ hollow core
+ end= fast growing [B tubulin]
+end also grows faster in low [Ca++]
-end = slow growing [a tubulin]
Dynamic instability
Alternate phases of slow growth and rapid depolymerization of microtubules.
Results from the hydrolysis of GTP-tubulin dimers, release of hydrolyzed phosphate, and subsequent release of GDP-tubulin subunits.
Cytoskeleton functions:
Cell movement, Support/strength, Phagocytosis, Mitotic spindle formation Cytokinesis Cell-to-cell / cell-to-extracellular matrix adherence Changes in cell shape
Role of microtubules in mitosis:
Actin filaments are the railroad tracks and pull chromosomes to opposite ends during mitosis
Mechanism of intraciliary transport
1:anterograde transport of cargos along a microtubule mediated by kinesin.
2: retrograde transport of cargo by Dynein.
3. Dissassembly of the raft protein complex-cargo-molecular motor machinery.
Then starts all over again w/ tubulin dimer and raft protein
Relate axonal transport to Intraciliary transport
The same except for the cargo comes from the Golgi of the axon nucleus
