Chapter 9-Lecture 2

Chapter 9-Lecture 2 - Intermediate filament assembly and...

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Intermediate filament assembly and disassembly . The name intermediate filament was established because these filaments were intermediate in size between icrotubules and tin laments Unlike MFs and MTs , IFs are a chemically heterogeneous group of structures that , in humans, are encoded by at least 50 differ3ent genes. microtubules and actin filaments. Table 9.1 summarizes the major mammalian intermediate filament proteins 1. Keratin types I and II - epithelia 2. Vimentin - mesenchymal cells esmin uscle 3. Desmin - muscle 4. Glial fibrillary acid protein (GFAP )- glial cells 5. Peripherin- astrocytes 6. Neurofilament proteins -neurons of central and peripheral nerves 7. Lamin proteins- all types of cells with lamin A associated with the nuclear envelope 8. Nestin- Neuronal stem cells Intermediate filament assembly and disassembly- The basic unit of IF sembly is thought to be a tetramer formed by two imers at become assembly is thought to be a tetramer formed by two dimers that become aligned side-by-side in a staggered fashion with their N– and C-termini pointing in opposite (antiparallel) directions
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A model for intermediate filament assembly and architecture Each monomer has a pair of globular terminal domains separated by a long "-helical region tep1) airs of monomers associate in (step1). Pairs of monomers associate in parallel orientation with their ends aligned to form dimers (step 2). Depending on the type of intermediate filament, the dimers may be composed of identical monomers (homodimers ) or nonidentical monomers (heterodimers ). Dimers in turn associate in an antiparallel, staggered fashion to form tetramers (step 3), which are thought to be the basic subunit in the assembly of intermediate filaments. The organization of the tetrameric subunits within the filament is shown in step 4. Antiparallel, staggered fashion to form tetramers A model for intermediate filament assembly and architecture
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Biotin labeled keratin injected in A; 20 minutes later incorporated into filaments Experimental demonstration of the dynamic character of Intermediate filaments (biotin labeled type I keratin).
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Microfilaments- Microfilaments are proximately nm in diameter d composed approximately 8nm in diameter and composed of globular subunits of the protein actin . In the resence of ATP these tin bunits polymerize presence of ATP, these actin subunits polymerize to form a flexible filament composed of two rands of tin olecules wound around each strands of actin molecules wound around each other in a double helix . The terms actin lament ” microfilament and F tin e all filament , microfilament and F actin are all synonyms for this type of two stranded filament.
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model of an tin lament The tin a) a model of an actin filament. The actin subunits are represented in three colors to distinguish the consecutive subunits more easily. The subdomains of one of the actin subunits are labeled 1,2,3, and 4.
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Chapter 9-Lecture 2 - Intermediate filament assembly and...

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