Lecture 16 Cytoskeleton - Biology 212 PDF

Cytoskeleton Biology 212: Cell Physiology Fall 2024 Professor Louise Goupil November 18-20, 2024 1  Cells are supported by the cytoskeleton Blue: nucleus Green: microtubules Red: actin filaments Cytoskeleton: network of p...

Cytoskeleton Biology 212: Cell Physiology Fall 2024 Professor Louise Goupil November 18-20, 2024 1  Cells are supported by the cytoskeleton Blue: nucleus Green: microtubules Red: actin filaments Cytoskeleton: network of protein filaments that extends throughout the cytoplasm Involved in organization of intracellular components, movement of cellular components, etc. 2  The cytoskeleton is involved in cell movement Movement of organelles/ vesicle trafficking Movement of cells (flagella, cilia) Movement in response to external signals iii in mn 3  Structural proteins tend to be be long filaments Chymotrypsin Actin Most proteins are globular (i.e. enzymes like chymotrypsin, left) Structural proteins form long chains/ filaments (actin, right) 4  There are three major types of protein filaments 1 intermediate width A large small 5  Intermediate filaments respond to mechanical stress Ytiility strength Intermediate filaments provide tensile strength; main function is to withstand mechanical stress when cells are stretched; rope-like, 10nm diameter Found throughout cytoplasm, within the nucleus (nuclear lamina), and sometimes anchoring neighbor cells 6 Intermediate filaments fold into coiled-coils Strands form alpha- helices that pair in dimers Hydrophobic amino acids (green) interact with each other to minimize contact with water 7  Intermediate filaments fold into coiled-coils Strands form alpha-helices that pair in dimers Hydrophobic amino acids (green) interact with each other to minimize contact with water 8  Intermediate filaments fold into coiled-coils Dimers wrap around each other in antiparallel fashion to form staggered tetramers, which associate to form a rope-like filament 9  Intermediate filaments make up nuclear lamina Nuclear lamina is formed from intermediate filaments; assembles and disassembles during cellular division as controlled by kinases 10  Intermediate filaments protect against mechanical stress filamentsabsorbs them prissonallowing tostretch Acts like rebar in concrete: 11  Intermediate filaments can be split into four classes Keratin filaments: almost every type of epithelial cell has a unique mixture Make up skin, hair, claws, tongue, cornea, etc. We have over 50 keratin genes! 12  Intermediate filaments can be split into four classes Epidermolysis bullosa Muscular Neurodegeneration Progeria simplex dystrophy Disruption of intermediate filaments can lead to disease 13 There are three major types of protein filaments 14  Microtubules organize eukaryotic cells Microtubules are critical in movement of organelles/ cell compartments, cell division (next chapter), movement of cilia/ flagella 15  Microtubules are hollow tubes made of tubulin Built from subunits of alpha- and beta-tubulin, two globular proteins bound by non- grows covalent interactions Filaments have a polarity: (+) end: beta-tubulin end, growing end (-) end: alpha-tubulin end, does not grow Ede Diameter of 25nm digital alphatubulin 16 Microtubules form from the centrosome Tubulin polymerizes from nucleation sites on a centrosome gamma y tubulin t.lt onoia in 17  GTP hydrolysis controls microtubule growth GTP-bound tubulin molecules bind to the growing end GDP-bound tubulin molecules are released from the growing end 18  GTP hydrolysis controls microtubule growth fantrosome Left: microtubules growing and shrinking Right: Microtubules extending out of the centrosome 19  Microtubules control cell shape Selective stabilization of microtubules can polarize a cell Microtubules persist when both ends are protected: one at the centrosome, and the other by a cap 20  Microtubules guide transport of organelles, vesicles, and macromolecules (-) end (+) end Most differentiated animal cells are polarized, driven by polarity of microtubules 21 Motor proteins on microtubules drive intracellular transport walkon ittarglo y ATP energy used to walk along microtubule 22 Motor proteins on microtubules drive intracellular transport Kinesins walk towards the (+) end Dyneins walk towards the (-) end 23 Cilia and flagella contain stable microtubules moved by dynein Cilia contain core of microtubules Beat in a whip-like fashion; cilia on respiratory tract sweep mucus by beating 24 Cilia and flagella contain stable microtubules moved by dynein whatallows them tomove Eukaryotic flagella and cilia contain characteristic “9+2” array with dynein arms 25 There are three major types of protein filaments 26  Actin filaments are essential for cell shape and movement Contractile Contractile Microvilli Filopodia bundles ring Actin filaments interact with actin-binding proteins, which can lead to the formation of stiff structures, temporary structures, or dynamic structures 27 Actin filaments are essential for cell shape and movement Polymer made up of globular actin subunits Like tubulin, actin filaments are polarized Diameter of 7nm 28  ATP hydrolysis controls actin polymerization Free actin carries ATP, hydrolyzes into ADP, reducing the strength of binding of monomers High concentration of actin: both ends grow Intermediate concentration of actin: treadmilling occurs Treadmilling: monomers removed from the minus end are added to the plus end 29  Comparing microtubule and actin filament synthesis i iiiiiiiiiiii iiif I Iii iii iiiin in c 30 I iiiiiiiiiiiiii.it treadmilling Actin-binding proteins control the behavior of actin monomers Enhanced actin Inhibited actin monomer monomer polymerization polymerization 5% of total protein in an animal cell is actin Half is in a filamentous form, half is free 31 Cell crawling depends on cortical actin Many eukaryotic cells move by crawling (i.e. amoeba, white blood cells) 1. Cells push out protrusions at leading edge (actin polymerization) 2. Protrusion attaches to surface 3. Cell drags itself towards protrusion 32  Cell crawling depends on cortical actin sane tingen it anti.tkIater ruffling tigersthat extendoutandattain Contains bundles of 10-15 actin filaments Above: fibroblast cell migrating, formation assisted by actin-binding proteins 33 Actin associates with myosin to form contractile structures Myosin uses energy from ATP to move towards the plus end of actin filaments Myosin-I molecules have a head domain and a tail - head binds to filament/hydrolyzes ATP and tail determines type of cargo hostabundant pullsthe active fillament Youthhyaline 34 Actin associates with myosin to form contractile structures Myosin-II molecules bind to two strands and move them each in opposite directions slidin fiim 35 Muscle contraction depends on interacting filaments of actin and myosin Myofibril Skeletal muscles are packed with myofibrils, the contractile elements of a muscle cell Each myofibril is made up of tiny sarcomeres, assemblies of actin and myosin-II 36 Muscle contraction depends on interacting filaments of actin and myosin Myosin fibrils are centrally positioned in each sarcomere The plus end of actin filaments is anchored to the Z-disc, while the minus end overlaps with myosin 37 Muscle contraction involves sliding of actin and myosin filaments notgrowing Actin filaments slide past myosin filaments, shortening the sarcomere Note: neither filament shortens! 38 Muscle contraction involves hydrolysis of ATP 1. Myosin head attached to actin 2. Myosin head binds ATP and releases from actin 3. Myosin head hydrolyzes ATP to ADP + Pi, but keeps both bound 4. Myosin head binds actin, releasing Pi, triggering the power stroke 1. Myosin head loses ADP, is attached to actin 39  Myosin cannot bind to actin in the absence of calcium myosin I iiifiii.tn Cat Tropomyosin without Ca2+ blocks myosin binding sites; shifts over when Ca2+ is bound 40 Summary of muscle contraction 41 Summary of muscle contraction 42  Study Guide: Cytoskeleton What are the different types of cytoskeleton? What roles are performed by each? Describe the general structure of each cytoskeletal element. How does the structure of this protein filament reflect its function? What would happen to the cell if components of the cytoskeleton were mutated or nonfunctional? Compare and contrast dynamic instability in microtubules and treadmilling in actin filaments. What proteins are associated with movement along microtubules and actin filaments? What direction(s) do these proteins move, and what powers their movements? Describe the general cycle of skeletal muscle contraction. What powers this? How does calcium play a role? 43  structure Functions cytoskeleton network of protein fillaments that extend flitting throughoutthe cytoplasm Eiiiii iii iii iii formslargehollowtubes involved in organization andmovement of Ttibules L tubulinheterodimer intracellular component again profendt minusend structural Proteins globular ex chymotrysin i if.fiIiiIIIIIIIii mama Intermediate Fillaments provide tensile strength streatched function withstand mechanical strength whencellsare where cytoplasm nucleus nuclearlamina anchoring neighboringcells foldinto coiledcoils strandsform alphahelices that pairintodimers hydrophobic aminoacids itx to avoidwater antiparallel fashion toform dimers wraparound eachother in staggered tetrameres which form ropelike fillaments Typesof Intermediate Fillaments alphahelix toplasmic 1 Keratinfilaments epithelialcells skinhair 2 vimentin vimentin related fillaments tissuecellsmusclecells connective 3 neurofilaments nervecells uclear 4 nuclear laming inanimalcells mutated or nonfunctional components lead todisease Microtubules criticalinmovementoforganelles celldivision movementofcilia flagella hollowtubes madeof tubulin built from subunitsof α and β tubulin plusend growingend βend grow α end anchored minusend doesn't gamma y tubulin nucleation site thatanchors microtubuleon acentrosomes GTPhydrolysis controls microtubulegrowth resides and macromolecules guide transportof organelles tubulinbinds hydrolyzes GTP  motorproteins useATP kinesins walktowards end dyneins walktowards end moves ciliaand flagella Actin essential for lellshape and movement intx w actinbinding proteins which can leadtothe formation of stiff structures temporary structures or dynamic structures madeup of globular actin subunits ATP hydrolysis controls actin polymerization reducesstrength freeactin carries ATP hydrolyzes App ofbondingmonomers conc ofactin BOTH ends grow intm conc ofactin treadmilling octors monomers removedfrom end addedto end Cell crawling dependanton cortical actin ATP to move towards plus end of actinfill vies energyfrom he domain binds tofillament hydrolyzes ATP d tail determines type of cargo most abundant sausing it to slide overthe Ihmthemythanellament myosin II bindsto 2strands to movethem in opposite directions muscle Contractions depend on interacting filaments of actin and myosin skeletalmuscles packedw myotibrils madeyqotmy1 itIl.aitit myosinfibrils centrally positioned in eachsactomere plusend of actinfillaments to 2 dis c anchored minusend overlaps Eff myosin myosin can't bindin the absence of calcium Cat muscle contractions involve sliding of actin and myosin filaments Protein Fillaments intermediate tensile strength fillaments coiledcoildimer intermediatewidth rope likestructure nuclear lamina microtubules hollowtube β tubulin heterodimer plus end minus end organelle cell movement use GTP dynamic instability Fitments t.TT iplling S.EE