{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lecture33 - LECTURE 33 13 November 2009(P J Hollenbeck...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
-1- LECTURE 33 13 November 2009 (P. J. Hollenbeck) BIOL231 Molecular motors & MTs: cilia and beyond Read: pp.583-90 / DVD 17.5-7/ Probs: 82-87 I. Cilia and flagella <In some cells we find moving systems that are specialized, stable, and highly organized. These have served as models for understanding the general principles of motor protein function and force generation. We saw this in sarcomeres of muscle cells, where the functions of actin and myosin were first elucidated. It is the same for MT-based movement. Here the most specialized and stable moving structure is the cilium or flagellum..> (A) General structure and function (1) Cilia are thin (0.25 ì m diam) surface protrusions found on many cells. They beat like tiny flexible oars, generating a current of liquid across the cell surface. In some cases (such as the ciliated epithelial cells that line your respiratory tract) the action of thousands of cilia per cell causes the fluid to move over the cell surface (here, mucus) . But for a ciliated single-celled eucaryote like Tetrahymena, the same rowing action moves the cell through the water that it lives in. A similar structure, the flagellum, beats to power the movement of protozoa or sperm cells, for example. (2) What supports this thin protrusion? Cilia and flagella contain a core of MTs and accessory proteins. It has a characteristic pattern of 9 MTs arranged in a ring around a central pair of 2 MTs. The MTs that form the ring have a special structure: they are “doublets,” in which one complete, or “A,” MT has a second, incomplete, or “B,” MT attached to its wall (see fig below). (3) Accessory proteins in the axoneme. The MTs of the cilium or flagellum have many accessory proteins that link them together, cap them, and make them extremely stable . Some of these proteins are large enough, or form complexes that are large enough, to be clearly visible in electron micrographs. The major ones are the nexin links that connect adjacent MT doublets to each other, the radial spokes that link doublet MTs to the central region, the inner sheath that links the two central MTs to each other, and the dynein arms that sit on the A-MTs and generate force for ciliary movement. (4) This complete assembly of proteins is very stable : you can shear the cilia off of a cell, use detergents to strip off the plasma membrane, and the scaffolding of proteins remains intact. This inner, cytoskeletal part of the cilium is called the axoneme.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
-2- <How are MTs, motors proteins, and accessory proteins organized to
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}