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Three types of filaments with diameters?
MF (5-7nm) < IF (9-11nm) < MT (25nm)
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Protein composition of the three filaments?
MF = actin, MT = tubulin, IF = tissue specific subunits (i.e. epithelial tissues = keratin)
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Rank MF, IF, MT in terms of the amount of associated proteins.
MF > MT > IF
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Which are types of proteins are globular and which are filamentous?
MF, MT = globular; IF = filamentous
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Rank the order of these proteins in terms of their subunit interactions to maintain stiffness?
IF > MT > MF
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Match physical properties to the right protein:
Similar to thick cables (resist tensile forces)
Stiff tubles (push and pull)
Railway system for intracellular transport
Bundle for strength/cross-link into networks
IF: similar to thich cables
MT: railway system, stiff tubes able to push and pull
MF: bundle for strength, x-link into networks
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Which proteins as vastly polymers and which are 50:50 monomer:polymer?
IF: mainly polymers; MF,MT are 50:50 monomer:polymer
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Characteristics of tubulin?
- Learning Slide:
- alpha-beta dimer (beta is positive end)
- highly conserved (any change in AA seq. will mess it up)
- important protein (10-20% of total soluble protein in brain)
- Beta subunit can carry GTP
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What is MTOC?
aka centrosome (centroile + gamma-tubulin)
Gamma-tubulin nucleates formation of MT (plus end away from MTOC)
Some MT have no identifiable MTOC (i.e. neurons)
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Dynamic Instability?
MT constantly scanning cytoplasm and changing length (slow assembly and catastrophic disassembly)
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How does dynamic instability work?
Growing: GTP tubulin molecules add to the MT faster than GTP hydrolysis.
Shrinking: protofilaments with GDP tubulin peel away because of curved shape (weak bonds)
- If GTP addition > rate of hydrolysis = GTP cap (growing)
- If GTP addition < rate of hydrolysis = GDP cap (disassembly)
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Cytoplasmic microtubules (polarity and type)?
single MTs radiating from MTOC; Negative end at the MTOC
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Neuronal MTs polarity (axonal and dendritic)
- Axonal: plus end away from cell
- Dendritic: mixed polarity
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Mitotic MTs polarity?
Double aster (centrosomes or MTOCs) of MTs with minus ends at the spindle poles
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Definition of Axoneme? 2 Examples of Axoneme?
- 9+2 MT structure (9 outer MT doublets and 2 single central MTs) for a total of 20 MTs
- Respiratory Cilia and Sperm Flagellum
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2 Examples of MT triplets?
- Centrioles and Basal Bodies (body of cilia & flagellum)
- 9 Sets of triplet MT (i.e. 27 MTs)
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Stability of Cytoplasmic MT, Mitotic MT, Neuronal MT, Axonemal MT, and Centriole, Basal Bodies?
All stabile except for Mitotic Spindle and Cytoplasmic MT.
- Mitotic Spindle: very dynamic (half-life of 15 seconds)
- Cytoplasmic MT: half-life of 10 minutes
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Which MT-associated proteins (MAPs) are spatially regulated?
- Tau- found only in axon
- MAP2 - found only in neuron dendrites and cell body
**Phosphorylation of MAP decreases their affinity for MT, decreasing stability (bc MAP generally increase stability)
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Stathmin?
curved MAP that prevents assembly of tubulin
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Kinesin-13?
Rips tubulin from (+) ends of MT
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Katanin?
Severs MT (like a sword)
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TIPs?
Caps MT and makes them stable; attaches to membranes
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Plectin?
Links/Binds MT to intermediate filaments (IF)
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Kinesin motor protein is ____ bound.
Dynein motor protein is _____ bound.
- Kinesin is (+) oriented (outward transport)
- Dynein is (-) oriented (inward transport)
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Positioning of organelles: Mitochondria, ER, Golgi, and MT-dependent IMF use which motor proteins?
Mito- Kinesin and Dynein
- ER - Kinesin
- MT-dependent IMF - Kinesin
Golgi - Dynein
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Nexin?
Protein linking adjacent "outer" doublets of cilia internal structure
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Mechanism of cilia/flagellum movement?
Nexin links convert sliding of dynein motor proteins into bending
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Minus directed Kinesin that aligns MT during spindle formation?
Kinesin-14
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Plus-end directed, tetrameric kinesin that seperates centrosomes?
Kinesin-5
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Mechanism of seperating chromosomes?
Kinesin-14 aligns MT, kinesin-5 seperates centromeres, and dyneins near cell membrane "pull" centrosomes (MTOC, or aster) towards them.
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Anaphase A vs. B?
Anaphase A: disassembly of kinetochore MT
Anaphase B: tetrameric kinesins slide polar MT apart and membrane bound dyneins pull aster MTs towards membrane
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MT related drugs can be carcinogens how? Why are they a good target for cancer treatment?
At low doses; involved with every phase of mitosis/meiosis
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Colchicine?
truncates the assembly process of MTs, but disassembly can still occur....net result = disassembly
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Vinca alkaloids?
doesn't allow tubulin to form MT by precipitating tubulin (no assembly)
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Taxol?
Doesn't let MT breakdown/disassemble (i.e. hyperstabilizes MTs)
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Chemotherapy best target the most ____ MT which are mitotic of cytoplasmic MT?
dynamic; mitotic (half-life is really short)
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Three categories of actin?
4 muscle isoforms: alpha (skeletal muscle, cardiac, visceral and cascular smooth muscle)
- 2 non-muscle isoforms:
- Beta-cytoplastic = cell cortex (cell structure)
- Gamma-cytoplastic = stress fibers
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Monomeric actin is globular or filamentous? polymer? Is it polar? ATPase?
- Monomeric: globular, polar, ATPase
- Polymer: filamentous, polar
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Assembly dynamics of actin?
- The arrow tip is (-) end, and back is (+) end
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Actin sequestering proteins?
- Profilin = like GEF, adds ATP where ADP was
- Cofilin +Thymosin = both block release of ADP and dont let polymer grow
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Nucleation complexes are needed for assembly. Examples include?
Arp 2/3 (helps actin branch off), tandem, and formin
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Stress fibers/cytosolic actin/migrating cells vs. microvilli, muscle, non-migrators
dyanamic vs. stable
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Actin stabilizing molecules (tropomyosin)?
Doesn't let ADP release; doesn't let other molecule (sever molecules bind)
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Actin severing molecules (Gelsolin, Cofilin)?
Gelsolin + Cofilin sever actin and cap + end to inhibit growth but Cofilin also rips loose the (-) end
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Actin example of motor protein?
Myosin
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Rho family GTPases of actin?
control actin assembly/disassembly via phosphorylating/dephosphorylating
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Listeria is a ____ infection that uses actin to _____ and hide from ___.
bacterial infection; actin; immune system
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Phalloidin (from actin lecture) is similar to ____ (from MT lecture) because it _____.
Taxol; hyperstabilizes actin (doesnt allow it from disassembling)
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Cytochalasin infection (actin lecture)?
Block polymerization
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What is the function of spectrin? Characteristics of spectrin?
Spectrin keeps cell membrane integrity. Contains binding domains at end and spacers inbetween.
**binding domain mutations are SEVERE (i.e. Duchenne's Muscular dystrophy)
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Diseases related to spectrin?
Hemolytic anemias:
1. Spherocytosis: pinching off of the RBCs (ankyrin binding domain messed up)
2. Elliptocytosis: RBCs lyse to due messed up spectrin
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Two types of muscular dystrophy? Differences?
Duchenne's MD: premature stop codon; actin binding domain mutation
Becker's MD: spacer domain repreats of spectrin
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6 types of intermediate filaments?
- Type I and II: Keratins (found in epithelial cells)
- Type III: Desmin (muscle), GFAP (glia), and Vimentin (mesenchymal, endothelial, etc.)
- Type IV: Neurofilaments (neurons)
- Type V: Nuclear lamins
- Type VI: Lens fibers
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The IF subunits are nonpolar or polar, linear or globular?
subunits are linear and polar
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IF assembly consists of?
parallel dimers (polar), tetramers (anti-parallel [non-polar] = unit-length filament)
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Growing assembly of IF (from subunit to IF)?
Dimer, tetramer, ULF, linear end-on-end addition ofULF (non-polar)
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ULF have the intrinsic ability to repair themselves?
Yes
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Phosphorylation of the head =?
Phorphorylation of the tail =?
- Phosphoryl. of the head = disassembly
- Phosphoryl. of the tail = creation of side arms
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Function of tonofilaments?
link cells together to transfer mechanical force
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Keratin mutations?
K5 or 14, basal layer mutation leads to epidermolysis bullosa simplex (EBS)
K1, or 10, stratum spinosum mutation leads to epidermolysis hyperkeratosis (EH)
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Desmin mutation?
Increased susceptibility to muscle damage (dystrophies)
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Lamin A laminopathy?
Hutchinson-Gilford progeria
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