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BIO130H1 (167)


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John Coleman

Pg. 965-988 The Cytoskeleton  Cytoskeleton: Network of filaments The self-assembly and dynamic structure of cytoskeleton filaments  3 types of cytoskeletal filaments 1. Intermediate filaments: provides mechanical strength 2. Microtubules: positions of membrane enclosed organelles and direct intracellular transport 3. Actin: determines shape of cell and required for cell locomotion  Need accessory protein to link the filaments to cell components  Accessory proteins are essential to control the assembly of the cytoskeleton and specific locations; this includes motor proteins convert ATP to ADP and P to move organelles along a filaments Cytoskeletal Filaments are Dynamic and Adaptable  Microtubules are found at the center and radiate outwards; so it can form a mitotic spindle during cell division  Can also form cillia and flagella on the surface of a cell  Tight bundles can transport materials  Plants cells: helps cell wall synthesis  Actin filaments: underlie plasma membrane of animal cells  Provides strength and shape of to its thin lipid bilayer  Form many different cellular projections  Ex. Dynamic structure: lamelipodia and filopodia  Actin based contractile ring: assembles to divide cell into two; allows for more stability  Microvilli: increases the surface area for absorption  Intermediate filaments: inner face of nuclear envelope  Form protective cage for DNA  In the cytosol they twist together to form long cables that connect nerve cells to the epithelial cells  Form tough appendages such as hair and fingernails  Example of a dramatic reorganization that occurs in cell division for fibroblast  Cell Division  Microtubules helps separates into the chromosomes mitotic spindles  Actin helps by forming a contractile ring allowing the cell to separate into two daughter nuclei  Many cells require rapid cytoskeletal rearrangements  Ex. Neutrophil, white blood cell The Cytoskeleton can also form Stable Structures  Cytoskeleton is responsible for cell polarity  Ex. Polarized epithelial cells: found in intestines; actin and intermediate filaments help maintain the difference between the apical surface (absorbs nutrients into the lumen of the intestine) and the basolateral surface (places nutrients to the bloodstream)  Ex. Budding yeast needs polarization to divide through budding Each Type of Cytoskeletal Filaments is constructed from Smaller Protein Subunits  Cells can disassemble through structural reorganization  Intermediate filaments are made up of smaller subunits that are elongated and fibrous  Actin and microtubules are made of globular subunits  Actin filaments have actin subunits  Microtubules filaments have tubulin subunits  Weak covalent bonds  Hundreds of accessory proteins are involved in the assembly or disassembly of filaments Filaments Formed from Multiple Protofilaments Have Advantageous Properties  Each subunit can be connected through a simple association reaction  Cytoskeleton polymers are made of multiple protofilaments: long linear strip that are joined at the end  Protofilaments can twist around to forma helix  Break the bon
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