Chapter 1 General Physiologic Processes Movements of ciliae and flagellae. Ciliae and flagellae are hair-like cell sur face projections. Their walls are formed by nine arrays of paired tubula structures,much in the same way as centrioles are formed by nine arrays of triplets(Figure 1-4). They grow from and are anchored to structures called basal bodies, whose structure resembles that of each member of a centriole pair. A motor protein, dynein, causes the bending and sweeping motion of these projections. The heads of this molecule project from one tubular struc ture of a pair to the other fiber, bind there, hydrolyze ATP, and use the ated energy to walk"along the fiber, thereby causing local bending Intracellular transport. Microtubules serve as binding sites for motor proteins that are able to hydrolyze ATP and use the liberated energy to cause motion and perform mechanical work. The kinesins move and can carry cargo toward the positive end of the microtubule The dyneins move and carry cargo in the opposite direction, toward the negative end of the microtubule Intermediate filaments. These elements of the cytoskeleton are 12 to 15 nm in diameter and include a variety of polymerized, mechanically stiff polypeptides, such as keratin, desmin, vimentin, lamin, and others. The relative abundance of different filamentous proteins varies among different cells: Keratin is found in epithelial cells, hair, and nails Desmin filaments link together the myofibrils in striated muscle cells Vimentin is found mostly in fibroblasts The lamins are the major constituent of the intermediate filament mesh that lines the inner surface of the nuclear membrane( the nuclear lamina) Figure 1-4 Schematic of a centriole. Nine groups of three microtubules run longitudinally in le walls of each centrioleMovements of ciliae and flagellae. Ciliae and flagellae are hair-like cell sur￾face projections. Their walls are formed by nine arrays of paired tubular structures, much in the same way as centrioles are formed by nine arrays of triplets (Figure 1–4). They grow from and are anchored to structures called basal bodies, whose structure resembles that of each member of a centriole pair. A motor protein, dynein, causes the bending and sweeping motion of these projections. The heads of this molecule project from one tubular struc￾ture of a pair to the other fiber, bind there, hydrolyze ATP, and use the lib￾erated energy to “walk” along the fiber, thereby causing local bending. Intracellular transport. Microtubules serve as binding sites for motor proteins that are able to hydrolyze ATP and use the liberated energy to cause motion and perform mechanical work. • The kinesins move and can carry cargo toward the positive end of the microtubule. • The dyneins move and carry cargo in the opposite direction, toward the negative end of the microtubule. Intermediate filaments. These elements of the cytoskeleton are 12 to 15 nm in diameter and include a variety of polymerized, mechanically stiff polypeptides, such as keratin, desmin, vimentin, lamin, and others. The relative abundance of different filamentous proteins varies among different cells: • Keratin is found in epithelial cells, hair, and nails. • Desmin filaments link together the myofibrils in striated muscle cells. • Vimentin is found mostly in fibroblasts. • The lamins are the major constituent of the intermediate filament mesh that lines the inner surface of the nuclear membrane (the nuclear lamina). Chapter 1 General Physiologic Processes 7 Figure 1–4 Schematic of a centriole. Nine groups of three microtubules run longitudinally in the walls of each centriole