Chapter 3: Cytoskeleton PDF

Chapter 3 : CYTOSKELETON Professor : Aboussaouira Module : Cell Biology & Genetic 1/2 Module : Cellular Biology Chapter : 3...

Chapter 3 : CYTOSKELETON Professor : Aboussaouira Module : Cell Biology & Genetic 1/2 Module : Cellular Biology Chapter : 3 Semester 1 www.um6ss.ma Academic year : 2024-2025 1  Cytoplasm Region between cell membrane and nucleus membrane Jelly-like fluid with Cell Organelles + Cytoskeleton + Nutrients 2  Cytoplasme = Hyaloplasme = cytosol Composition: Water (70%) Small molecules (low MW) : ions, gaz, oses, glucose, amino acid, fatty acid, uree, glycerol, … Large molecules or Macromolecules (High MW) : Proteins – Lipids – Carbohydrates – Nucleic acid (RNA) Inert inclusions : forme of cell reservation inert = NON LIVING => forme of cell reservation Proteins : make a cylinder = proteasome Lipids : form a droplets : lipid droplets Carbohydrates : forme little roses = rosettes (little clouds) Filamentous Proteins : Cytoskeleton Cytoplasme Functions : Metabolism 3 Cytoskeleton under MF after specific labelling  Cytoskeleton Network of filamentous proteins Extending within cytoplasm = mechanical support Maintain cell shape & 3D shape Ensure cell motility, chromosomes migration during mitosis, organelles movement, biochemical reactions  Types of cytoskeleton Actin Microfilaments (AF): 5-8 nm Ø Intermediate Filaments (IFI): 8-10 nm Ø Microtubules (MT) : 20-30 nm Ø Cellular cortex MT AMF IF 6 Cytoskeleton in MET & FM 7  AMF structure and nucleation Actin Monomere : G-Actin : globular protein with 1 ATP groove Actin polymer : several G Actin bind to each others to form F-Actin with ATP grooves on the same side = Actin nucleation or assembly that involves ARP2/3 (moule) and forms 2 twisted chains complex 8 Actin Polymerization/Depolymerization 9 ARP 2/3 10 Actin filament Polymerization/Depolymerization 11  Actin Filament Polymerization It depends on actinG/ATP concentration : If G/ATP increases => polymerization If G/ATP decreases => depolymerization 12 MFA Roles 13  AMF Roles Maintain 3D shape : by cellular cortex = layer of actin microfilaments under MP Cytoplasmic currents : guidance and movement of molecules & organelles Supporting cell structures: microvilli (Cell intestin and kidney) Vesicular exchanges : endo/exocytosis vesicles tafic Cell division : contractile ring during cytodieresis Diapedesis : extravasation of white blood cells outside vessels Cell migration: many cells such as macrophage by polymerization and depolymerization of MFA.  AMF functions Microvilli Supporting 3D shape Cell migration Cytokinesis 15 Cell Migration 16 Actin Microfilaments 17  Actin filament associated proteins ARP2/3 : protein complex for assembly CapZ : Stoped AM polymerization Tropomyosin : protecting from depolymerization Troponin : protect myosin site Myosine II : motor protein, muscle contraction Severin : cut AMF to create new extremities  Actinin, Fimbrin, Filamin : Angulation proteins Myosin I : links cellular cortex to membrane (to spectrin in red cell, dystrophin in muscle cells) Angulation proteins : Fimbrin, filamin, actinin 18 19 20  Myosin Family Myosin I : link AMF to membrane Myosin II : muscle contraction Myosine IV : motor protein, ensures molecules or organelle transport (train car) 21  Small GProteins Bring GTP energy to cytosolic mechanisms Bind GTP (active) or GDP (inactive) Ras : for signaling pathways Rac : forms lamellipods to allows cell migration Rho : forms filaments bundles (package) for cell tension Cdc42: fillipods for migration, polarity, cell cycle Rab : vesicles trafic Ran : molecules transport into & out of nucleus 22 23 24  MT Structure and Assembly Monomer : 2 types of tubulines α and β Polymer nucleation : Tubulins α and β combination => tubulin dimers (using GTP) Dimers combination using GTP => protofilament (3-4 dimers) 13 protofilaments bind to γTURC (Tubulin Ring Complex) => MT 25 26 MT stabilizated by MAP2 27  MT Polymerization It depends of equilibrium between free and linked tubulin If free tubulins in GTP form increase => polymerization If free tubulins in GTP form decrease => depolymerization Normally there is a balance between poly and depolymerisation If Polymerization / Depolymerization becomes => MT becomes unstable, collapses : disaster phenomenon Various causes of disaster phenomenon : decrease in free GTP tubulins, disappearance of MAP2, tension into cytoplasm, islands of GTP in MT 28 MT disaster phenomenon 29  MT associated proteins 1. γTURC : MT nucleation 2. MAP2 : MT stability 3. Kinetochore : attach chromosome to mitotic spindle during mitosis 4. Motors Proteins : Transform chemical energy (ATP or GTP) to mechanical energy 2 types, Kinesin and Dynein, with globular parts on MT (head) and cytosolic part with a cargo seat 30 Fig. 6-21 Vesicle ATP Receptor for motor protein Motor protein Microtubule (ATP powered) of cytoskeleton (a) Microtubule Vesicles 0.25 µm (b)  Kinesin and Dynein Nucleus Cell membrane 32  AMF Roles Maintain 3D shape Cytoplasmic currents : guidance and movement of molecules & organelles Supporting cell structures: Cilia, Flagela, Axon, centriole Vesicular exchanges : endo/exocytosis vesicles tafic Cell division : MT form Mitotic spindle Diapedesis : extravasation of white blood cells outside vessels Cell migration: many cells such as macrophage by polymerization and depolymerization of MFA.  Cilia and Flagella MT control cilia and flagella beating Cilia (trachea) and flagella (spermatozoe) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 35 Fig. 6-22 Centrosome Microtubule Centrioles 0.25 µm Longitudinal section Microtubules Cross section of one centriole of the other centriole  Pharmacological effects on MT Colchicine antimitotic that binds to free tubulin and prevents its polymerization Others alkaloids used in chemotherapy (vimblastin, vincristin, podophyllin) are also antimitotics Taxol (breast cancer, extract of Yew tree) prevents MTs depolymerization of mitotic spindle and stops cell divisions 37 38  INTERMIDIATE FILAMENTS (IF) Stable (never polymerize/depolymerize) Thrue Cytoskeleton : maintain cell shape Form nuclear lamina in nucleus : 3 lamins (A,B,C) form a laminar layer, against inner nucleus, reinforces nuclear envelope Used to determine cancer type by IHC (immunohistochemistry) 39  IF families Cytokratin : in epithelia cell, 20 types, specifie cancinoma tumor Desmin : IF in muscle cell, myoblastome Vimentin : Connective tissu, sarcoma Neurofilaments : in neurons, neuroblastome GFAP (Gliale Fibrilary Activating Proteins) : in gliary nerve cell, glioma 40  IF structure and assembly Always made up of filamentous monomers with two heads (Regardless of the filament type) Two monomers dimerize, then tetramerize Tetramers alternate in space & form a rope : IF 41  IF Functions Cell Morphogenesis : IF form cell Scaffold Ex : in muscle cell IF provides actin & myosin orientation Tau mice (desmin-, normal actin & myosin): disturbed ctoskeleton organization => no sarcomer, no contraction Cell Resistance : IF link all desmosomes (CAM) and hemidesmosoes to each others If affected links => epidermolysis bullosa (genetic abnormality) 42