26. The discovery that the intermediate filament protein keratin is essential fo

Question

26. The discovery that the intermediate filament protein keratin is essential for mechanica epithelial cell layers was made in a. cell cultures. b. organ cultures. c. small invertebrates d. transgenic mice. a' 27. The concentration of actin monomers at which the rate of polymerization into filaments equais te rate of depolymerization is called theConcentration. a. equilibrium b. dynamic c. steady-state d. critical 28. Actin exists in cells in two major forms called a. monomers and dimers. b. alpha-actin and beta-actin. c. G actin and D actin. d. G actin and F actin. 29. The phenomenon that takes place at a concentration of free actin at the midpoint between the critical concentrations of the barbed and pointed ends of an actin filament is called a. assembly. b. dynamic instability. c. treadmilling. d. disassembly 30. Actin filaments are stabilized by a. cofilin. b. gelsolin. c. thymosin. d. tropomyosin. 31. Actin filaments are anchored at junctions called a. adherens junctions. b. tight junctions. C. d. gap junctions. 32. Microtubules are assembled from a. alpha-tubulin dimers. b. beta-tubulin dimers. C. c. alternating alpha-tubulin dimers and beta-tubulin d. dimers of alpha and beta-tubulin. chayvior in which some microtubules areraplsy depolymrizing and some are 33. The microtubule behavior in which some microtubules are growing is called a. an equilibrium state. b. dynamic instablity. d. recycling. 2016 Sisascy

Explanation / Answer

26. The discovery that the intermediate filament protein keratin is essential for mechanical strength of epithelial cell layers was first made in transgenic mice through the expression of mutant keratins. Therefore, your answer is (d)

27. At critical concentration the rate of polymerization of actin monomers into filaments at one end becomes equal to the rate of depolymerization of actin filaments into monomers at the other end. Therefore, your answer is (d)

28. In cells, actin can be present either as a free monomer form called G-actin (globular) or as part of a linear polymer microfilament called F-actin (filamentous). Therefore, your answer is again (d)

29. Treadmilling is the phenomenon that takes place at the midpoint between the critical concentration of the barbed and the pointed ends of actin filament. It occurs when one end of a filament grows in length while the other end shrinks resulting in a section of filament seemingly moving across a stratum or treadmilling. Therefore, your answer is (c)

30. Tropomyosin stabilizes the conformation of actin filaments. Therefore, your answer is (d)

31. Principal interactions of structural proteins take place at cadherin-based adherens junction. The actin cytoskeleton is similarly anchored to regions of cell-cell contact called adherens junctions. Therefore, your answer is (a)

32. Microtubules are made up of polymerised alpha- and beta-tubulin dimers. These alpha/ beta-tubulin dimers polymerize end-to-end (alternately) to form a single microtubule. Therefore, your answer is (c)

33. Dynamic instability is the coexistance of rapid depolymerization at one end and the growing (by polymerization) at the other end a microtubule. Therefore, your answer is (b)

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