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Lecture 10

Lecture 10: Intermediate filaments

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Biological Sciences
Tanya Da Sylva

What is the cytoskeleton? Extensive protein network Made on free ribosomesin the cytoplasm, no targeting sequence Three main components: 1.Microtubules 2.Actin 3.Intermediate Filaments Cytoskeleton -Functions Scaffold structural support and cell shape Internal framework organize organelles within a cell Movement directs cellular locomotion and movement of materials within the cell Machinery for cell division Key to Cystoskeletal Functions: 1) Structure and Support 2) Intracellular transport 3) Contractility 4) Spatial organization Memorize table 9.1 Actin: Flexible, helical is used more for contractility and mobility 3) Intermediate Filaments Heterogenous group of proteins, divided into five classes ~ 10 nm in diameter intermediate in size between microtubules and actin(micro filaments) 50 gene products Mainly structural support Types I IV form filaments Type V (lamins) are present in the inner lining of the nucleus Monomers have a long a-helical stretch Fibrous proteins strong, resistant to stretch Gives cellscell structures strength Monomers form homodimers parallel to one another Dimers come together antiparallel to form tetramers Tetramers then polymerize into filaments Both tetramer and IF(intermediate filament) lack polaritylack direction Assembly and disassembly are controlled by: phosphorylation and dephosphorylation Generally for cell strength not used for intracellular transport etc. Neurofilaments-important for integrity of axons Laminsinner nuclear membrane cytoskeleton: determines shape of nuclear envelope Keratin: Keratin: main protein of skin cells (keratinocytes) Skin is made of many layers constantly dividing Makes huge amounts of keratin As skin cells are pushed towards surface they undergo apoptosis ; programmed cell death
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