6. Cytochalasin B strongly inhibits certain forms of cell motility. In classic e

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6. Cytochalasin B strongly inhibits certain forms of cell motility. In classic experiments that defined its mechanism, short lengths of actin microfilaments were decorated with myosin heads and then mixed with actin subunits above the critical concentration in the presence (+) or absence-) of cytochalasin B Assembly of actin microfilaments was assayed by examining samples by electron microscopy. The figure to the right shows results describing the appearance of actin microfilaments formed in the presence and absence of cytochalasin B. The decorated actin microfilaments (gray circles + lines) present before the addition of actin monomers are shown at the top of each set of three. Microfilaments present after increasing times of incubation with actin monomers (red circles) are shown in the next two rows. minus plus A. (3pts) Please propose a molecular mechanism for how cytochalasin B affects the dynamics of actin microfilaments that is consistent with the EM data B. (2pts) Why was it informative to decorate the actin microfilaments with myosin heads before adding mixing with actin subunits? 7. (4pts) Many transport vesicles carry both kinesins and dyneins. Please provide a reason why this might be the case

Explanation / Answer

ANS 6 A) Actin filaments participate severely in lots of factors of neuronal boom and development. mobile actin exists in each monomeric (g-actin) and polymerized (f-actin) shape. equilibrium between these states is atp established and controlled by using a variety of actin-associated proteins. actin filaments can be both solid, with their lengths exactly designated, or dynamic, undergoing rapid polymer elongation and shrinkage (1, 2). stable actin filaments underlie specialised mobile structures, like muscle sarcomeres, brush border microvilli, and hair-cellular stereocilia. dynamic actin filaments mediate diverse styles of cellular motility, including migration, membrane ruffling, and filopodial extension. activities mediated by using dynamic actin filaments are arrested rapidly inside the presence of actin assembly inhibitors (aais) like the cytochalasins and latrunculins (3, 4). these instructions of compounds work by means of wonderful mechanisms to induce net depolymerization of dynamic actin filaments, however they have got relatively little effect on extra solid filaments that flip over slowly.

ANS 6 B) The actin microfilaments are decorated with myosin heads before adding mixing with actin subunits because the polymerization system is monitored through viscometry, sedimentation, and fluorescence spectroscopy. whilst actin filaments become long enough to become entangled, the viscosity of the solution will increase, which is measured as a decrease in its flow rate in a viscometer. the idea of the sedimentation assay is the capacity of ultracentrifugation to pellet f-actin but no longer g-actin. the 0.33 assay uses g-actin covalently categorised with a fluorescent dye; the fluorescence spectrum of the modified g-actin monomer changes while it's miles polymerized into f-actin. those assays are beneficial in kinetic research of actin polymerization and in the course of purification of actin-binding proteins, which pass-link or depolymerize actin filaments.

ANS 7) inside cells, membrane-bounded vesicles and proteins are frequently transported many micrometers along well-described routes within the cytosol and introduced to specific addresses. diffusion by myself can't account for the rate, directionality, and locations of such shipping approaches. early video light microscopy studies confirmed that these long-distance movements comply with immediately paths in the cytosol, frequently along cytosolic fibers, suggesting that transport includes some sort of tracks. subsequent experiments, using nerve cells and fish-scale pigment cells, first demonstrated that microtubules characteristic as tracks inside the intracellular transport of membrane-bounded vesicles and organelles, and that movement is propelled via microtubule motor proteins.

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