SI session Dec. 4 Ch. 16 answers

SI session Dec. 4 Ch. 16 answers - Kaiser Imam December 4...

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December 4, 2007 BIOL 215 SI Session Chapter 16 Chapter 16: Cellular Movement 1. List some similarities and differences between cilia and flagella: Both cilia and flagella moved by the operation of axonemal dynein. Cilia and flagella mainly differ in their relative length, the numbers of each per cell, and their mode of movement. Both cilia and flagella are about 0.25 μm in diameter, but cilia are about 2-10 μm long while flagella can range from 10-200 μm in length. A cell is usually limited one or a few flagella. In contrast, ciliated cells can have cilia in large numbers. Cilia have an oarlike pattern of beating that involves a power stroke perpendicular to the cilium that generates a force parallel to the cell surface. Flagella have a more undulatory movement that generates a force parallel to the flagellum. This causes the cell to move in the same direction as the axis of the flagellum. 2. Describe some of the common structural features of cilia and flagella. Cilia and flagella have a common structure consisting of an axoneme, or central cylinder of specifically-arranged microtubules, and a basal body inside the cell. The axoneme is covered by an extension of the plasma membrane. The axoneme has a “9+2” arrangement of microtubules, which consists of nine outer doublets of tubules arranged in a circle around the edge of the axoneme and a central pair of two microtubules in the center. Each outer doublet has one complete MT called the A tubule and one incomplete tubule called the B tubule. The A tubule has the characteristic 13 protofilaments of a microtubule, but the B tubule has only 10 or 11 and shares part of its wall with the A tubule. The tubules of the central pair are both complete with 13 protofilaments each. The basal body is used to anchor the cilium or flagellum to the cell and has the same structural organization as a centriole. It consists of nine outer triplets but no central pair of MTs. Each triplet has two complete MTs and one incomplete tubule. 3. What causes cilia and flagella to bend? Movement in cilia and flagella is caused by axonemal dynein, which causes MTs to slide past each other. Structures called sidearms are found in the axoneme and project out from each of the A tubules in the nine outer doublets. The sidearms contain inner and outer dynein arms that are spaced along the MTs at regular intervals. The hydrolysis of ATP by dynein causes the two microtubules of each outer doublet to slide past one another. In an isolated doublet this would result in a change in the length of the doublet. However, doublets in cilia and flagella are not isolated but are connected in a variety of ways that prevent sliding. The sliding movement is converted to a localized bending because the doublets are connected to the central pair by radial spokes and to each other by crosslinks. 1
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SI session Dec. 4 Ch. 16 answers - Kaiser Imam December 4...

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