Cytoskeleton I Flashcards
Roles of cytoskeleton
Cell polarity
Directional migration
Formation of mitotic/meiotic spindle
Chromasome seg
cytokinesis
Intracellular transport, exo/endo cytosis
Why do cytoskeletal components have dif distributions
Important for cell shape, polarity, and tissue formation
What are cytoskeletal structure made of
Small protein subunits Noncovalent polymers Dynamic Accessory proteins regulate sites and state of assembly Adaptable
Intermediate filaments key facts
Intermeidate in size, more stable
Major components of cytoskel and nuclear boundary
Protection from mechanical stress-within cells (surround nun and extend to periphery) and at junction of cell and ECM
Role insignalling and gene reg networks
No motor
Intermediate filaments strucutre
Include keratins, near filaments, nuclear lamins
Two chained coiled coil that assembles to form tetramere-tetramer forms higher order assemblies-held together by hydrophobic interactions
N anC terminal ends are globular-coiled coil region interrupted by linker domains
Intermediate protein assembly
Antiparallel tetrameters
not polar
Actin key facts
Polyermeric and globular (g-actin)
Polar-ends are distinctly different
Bound nucleotide (ATP/ADP)
Plus end (barbed) is fast growing Minus end (pointed) is slower growing)
Helical filament
Binding proteins modify filament dynamics and higher order assemblies
Actin elongation
Faster at plus (barbed) end
Rate limiting step is formation of nucleus (3 subunits)
ATP actin is preferentially added to barbed end
-hydrolysis not required for polyermaization-bound nun influences stability
Each actin filament has ADP-actin, except for extreme barbed end
What do proteins that bind to actin do
Bind to one end (cap)
Sever filaments
Cross link
Anneal etc
MT and actin filament parallels (6)
Both form globular protein by condensation/polymerization mech to form polar structure
Both have pref end of monomer addition
Nuc hydroylsis lags behind polyermization elaving ATP/GTP cap at plus end
Nucleotide at plus end determines stability
Dynamics and state of assembly reg by MT binding proteins
Structures are NOT RELATED
Tubulin and MT structure
Two subunits
- b binds to GTP
- GTP hydrolyzed during polymerization which is at plus end of molecule
- polyermerizes to long protofilaments in MT
Polar
Nothing on the inside
Tubulin and MT function
Vesicular and organelle transport, from mitotic spindle, cilia, and flagella, entriole and basal bodies
What structures are made of MT’s
cilia, flagella, centrioles, and basal bodies
Have knobs coming out of outer doublet (dyenine)
Primary cilium
Apparent on most cells
Non-motile
Usually 1 per cell
Sensory organellles
Central player in dev signaling pathways
No central pair, no knobs oming out of outer doublet (no dyeing)
Centrosome Facts
MT organizing center-all MT eminate from here
- Minus end is located here
- gamma tubulin ring complex that nucleates the 13 protofilaments of MT’s and caps the - ends
- +ends oriented towards cell periphery
- centrioles duplicate at beginning of S phase of mitosis
Mitotic spindle
Kinetochore attaches to plus end of MT and enables alignment on metaphase plate
Plus ends interact with other plus ends of other centrioles
3 types of MT and functions
Astral-go in every direction thats not metaphase plate
Kinetochore-attach to kinetochore
Interpolar-attach to other plus ends
NTP to NDP
Release takes place after polymerization
Results in polarity
Addition is fast on +, slow on -
Nuc cap (with GTP or ATP) at +
GDP or ADP on -
T form vs D form
NTP or NDP
minus end addition is slow-hydrolysis catches up
Plus end addition is fast-hydrolysis lags behind
Dynamic instability
Plus end transitions between growth and shrinking
GTP tubulin cap stabilizes plus end
GDP tubulin subinits at the plus end destabilize-rapid depolymerization (catastrophe)
MAPS
Microtubule Associated Proteins
Regulate state of MT assembly
Stabilize or destabilize plus of minus ends
Bind to side-stabilize by side binding or bundle formation
Sever
Tau protein
a type of MAP
Connections between microtubules
Tangled in alzheimers
When microtubules reach cell periphery
+ tip proteins inhibit catastrophes
+tip protein bind and track the + end of growting MT
Communicate and connect with cell cortex to transport materials to cortex and interact with actin cytoskeleton
Capture chromosomes during mitosis-association with kinetochore
Phallodin
Binds and stabilizes actin filaments
-death angel mushroom
Death angel mushroom
contains fallopian and amanitin (RNA pol II inhibitor)
Colchicine
Depolymerizes MTs
Taxol
Binds and stabilizes MTs
-widely used anti cancer drug-inhibit cell division
Cell migration facts
Occurs during development-pathfinding and targeting of neurons
Chemotaxis
Tissue formation, repair, remodeling-migration of cells to repair skin won
Cancer-metasis of oncogenic cells
Chemotaxis
Migration of neutro[hols to sites of infection
Cell migration movement of leading and lagging edge
Leading edge is driven by actin polymerization
Tail follows with actin-myosin II
Cytoskeleton dependent movements
Cellular movement can be motor driven or polymerization driven
Intracellular transport can be motor driven or polymerization driven
Pathrgens usurp ceullular machinery
Neutrophil chasing bacterium
Neutrophils protect body from bacteria that enter body though skin
Chase bacteria by chemotaxis
- actin poly at leading edge
- actin and myosin II dependent tail contractions
What is role of dynamic actin filaments in cellular functions
Actin polyermation alone can drive cell migration
Some bacteria commandeer the cell’s actin polymerization machinery during infection
Actin polymerization provides force for movement by
Elongation of barded end
Need many growing ends
- nucleate more actin filaments
- Sever existing filaments to create more barbed ends
- Form braces from existing actin filaments
Arp2/3 complex-Nucleates filaments from the sides of actin filaments-make complex branched structures
Arp2/3 complex
Nucleates filaments from the sides of actin filaments-make complex branched structures
Rho dependent signalling cascade
Regulates dendritic nucleation
Arp2/3 requires activition for efficient nucleation of branched filaments-nucleated filaments push against cell membrane
Activators-downstream in rho family of small GTP ases signaling cascade
Localizes activation at cell membrane, site of protrusion
Arp2/3 dependent polymerization is involved in
Neutrophil migration to site of infection
Wound healing
Invasion of metastatic cancer cells
Bacterial infections
endocysosis
many more
Listeria
Infects epithelial cells-hijacjs Arp2/3 dependent actin polymerization machinery
Actin filaments polymerize-form a tail that propels the bacterium through cytoplasm like a comet
