Lecture31 - LECTURE 31 09 November 2009 (P. J. Hollenbeck)...

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LECTURE 31 09 November 2009 (P. J. Hollenbeck) BIOL231 The Cytoskeleton: Formation of Specialized Actin Structures Read: chap. 17: 590-592; 595-602 Probs: 76-80; Exam IV’06, #3 <We finished last time looking at regulation of cytoskeletal assembly and disassembly. This involved both XTP hydrolysis and the action of 4 classes of accessory proteins. These interacted with actin (or MTs, which have similar classes of regulatory proteins) and modified their assembly in various ways. But other classes of accessory proteins affect the organization of actin filaments and MTs. These proteins contribute to the formation of complex, specialized structures – structures more complex than could be formed form from pure actin or tubulin in vitro .> I. Building actin-based cytoskeletal structures (A) Compare and contrast types of structures (1) The basic cytoskeletal subunit proteins – intermediate filament protein, actin, and tubulin – are joined by many accessory proteins to form specialized structures in the cell. Some of these are very stable and can last the life of the cell, while others are highly dynamic and transient, existing for only a few moments, or only under particular conditions, or for a particular part of the cell cycle. (2) The accessory proteins that help to construct transient cytoskeletal structures typically are tightly regulated, responding to cell signaling events such as phosphorylation by kinases, Ca signals, etc. A few examples of stable and transient cytoskeletal structures: actin-based MT-based Transient, highly dynamic: lamellipodium = the leading edge of a crawling cell like a white blood cell; it is supported by a broad, branched actin filament network mitotic spindle = bipolar array of MTs that arises at prophase, sorts chromosomes into daughter cells during metaphase/anaphase, and rapidly disassembles during telophase Stable, long- lasting sarcomere = the highly-ordered array of actin and myosin filaments that produces force in muscle contraction ciliary or flagellar axoneme = parallel, cross- linked array of MTs that interacts with dynein motors to produce the beating of cilia and flagella <To understand the principles of building specialized cytoskeletal structures, let’s first focus on actin and the accessory proteins that interact with actin filaments to form complex structures with varied properties:> (B) Actin binding proteins (more!) [ fig 17-31 ] <We’ve already discussed 4 types that interact with actin filaments to affect their assembly properties:
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Lecture31 - LECTURE 31 09 November 2009 (P. J. Hollenbeck)...

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