Lecture 16 (Oct 5)

Lecture 16 (Oct 5) - Biological Sciences 110A: Introduction...

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Lecture 16: Intermediate and Actin Filaments The “rope-like” intermediate filaments (IF) Cell-type specific IF families IF structure and function Actin forms microfilaments Actin-related proteins (ARPs) nucleate assembly Actin-binding proteins bundle filaments Role of the actin cytoskeleton Biological Sciences 110A: Introduction to Biology Kendal Broadie Reading in Chapter 9 (357-368) Karp
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Most eukaryotic cells contain a cytoskeleton composed of three protein filament systems Microtubules Intermediate filaments Microfilaments 25 nm 25 nm 25 nm 25 nm dia. Tubulins ( α and β ; MAPs and motor proteins) Vesicle transport, cell polarity, and division 9-12 nm dia. Cell-type specific subunits Elasticity and tensile strength (“rope function”) 6-7 nm dia. Actin (myosin motor, and accessory proteins) Contraction, transport, locomotion and division
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Comparison of Microtubules and Intermediate Filaments Fig. 9.40 Karp
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Intermediate Filaments: “rope-like” protein polymers conferring mechanical strength Polymers made of different repeated monomer subunits 5 major families of proteins; cell-type specific Unlike MTs, do not possess any recognized organizing center in the cell Radiate throughout the cell; abundant around organelles (esp. nucleus) and membrane Especially abundant is tissue encountering mechanical stress (e.g. muscle, skin) See Fig. 9.43 Karp
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Intermediate filaments are composed of cell-type-specific subunits Cytoplasmic IFs largely restricted to higher eukaryotes (vertebrates) IFs are very insoluble (resistant to salt and non-ionic detergents) Three cell-type-specific classes of cytoplasmic IFs: Keratins in epithelia Diverse family of related proteins Vimentin-family in connective tissue, muscle, and glia Vimentin in connective tissue Desmin in muscle Glial fibrillary acidic protein (GFAP) in glia Neurofilaments in neurons Neurofilament triplet proteins (Heavy, Intermediate, and Light chains) provide structural support Nuclear lamins in all nucleated cells (except yeast?): support nucleus Sequence comparison suggests that IF proteins diverged from common ancestral protein (~35% aa identity overall, up to ~70% in sub-families)
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Some examples of IFs MTs NFs Keratin in cultured skin cell Neurofilaments Neurofilaments (EM section) Nuclear lamina
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This note was uploaded on 04/07/2008 for the course BSCI 110B taught by Professor Due during the Spring '08 term at Vanderbilt.

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Lecture 16 (Oct 5) - Biological Sciences 110A: Introduction...

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