Microtubules, IMF, MF
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Three types of filaments with diameters?
MF (5-7nm) < IF (9-11nm) < MT (25nm)
Protein composition of the three filaments?
MF = actin, MT = tubulin, IF = tissue specific subunits (i.e. epithelial tissues = keratin)
Rank MF, IF, MT in terms of the amount of associated proteins.
MF > MT > IF
Which are types of proteins are globular and which are filamentous?
MF, MT = globular; IF = filamentous
Rank the order of these proteins in terms of their subunit interactions to maintain stiffness?
IF > MT > MF
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
Which proteins as vastly polymers and which are 50:50 monomer:polymer?
IF: mainly polymers; MF,MT are 50:50 monomer:polymer
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
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)
MT constantly scanning cytoplasm and changing length (slow assembly and catastrophic disassembly)
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)
Cytoplasmic microtubules (polarity and type)?
single MTs radiating from MTOC; Negative end at the MTOC
Neuronal MTs polarity (axonal and dendritic)
- Axonal: plus end away from cell
- Dendritic: mixed polarity
Mitotic MTs polarity?
Double aster (centrosomes or MTOCs) of MTs with minus ends at the spindle poles
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
2 Examples of MT triplets?
- Centrioles and Basal Bodies (body of cilia & flagellum)
- 9 Sets of triplet MT (i.e. 27 MTs)
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
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)
curved MAP that prevents assembly of tubulin
Rips tubulin from (+) ends of MT
Severs MT (like a sword)
Caps MT and makes them stable; attaches to membranes
Links/Binds MT to intermediate filaments (IF)
Kinesin motor protein is ____ bound.
Dynein motor protein is _____ bound.
- Kinesin is (+) oriented (outward transport)
- Dynein is (-) oriented (inward transport)
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
Protein linking adjacent "outer" doublets of cilia internal structure
Mechanism of cilia/flagellum movement?
Nexin links convert sliding of dynein motor proteins into bending
Minus directed Kinesin that aligns MT during spindle formation?
Plus-end directed, tetrameric kinesin that seperates centrosomes?
Mechanism of seperating chromosomes?
Kinesin-14 aligns MT, kinesin-5 seperates centromeres, and dyneins near cell membrane "pull" centrosomes (MTOC, or aster) towards them.
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
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
truncates the assembly process of MTs, but disassembly can still occur....net result = disassembly
doesn't allow tubulin to form MT by precipitating tubulin (no assembly)
Doesn't let MT breakdown/disassemble (i.e. hyperstabilizes MTs)
Chemotherapy best target the most ____ MT which are mitotic of cytoplasmic MT?
dynamic; mitotic (half-life is really short)
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
Monomeric actin is globular or filamentous? polymer? Is it polar? ATPase?
- Monomeric: globular, polar, ATPase
- Polymer: filamentous, polar
Assembly dynamics of actin?
- The arrow tip is (-) end, and back is (+) end
Actin sequestering proteins?
- Profilin = like GEF, adds ATP where ADP was
- Cofilin +Thymosin = both block release of ADP and dont let polymer grow
Nucleation complexes are needed for assembly. Examples include?
Arp 2/3 (helps actin branch off), tandem, and formin
Stress fibers/cytosolic actin/migrating cells vs. microvilli, muscle, non-migrators
dyanamic vs. stable
Actin stabilizing molecules (tropomyosin)?
Doesn't let ADP release; doesn't let other molecule (sever molecules bind)
Actin severing molecules (Gelsolin, Cofilin)?
Gelsolin + Cofilin sever actin and cap + end to inhibit growth but Cofilin also rips loose the (-) end
Actin example of motor protein?
Rho family GTPases of actin?
control actin assembly/disassembly via phosphorylating/dephosphorylating
Listeria is a ____ infection that uses actin to _____ and hide from ___.
bacterial infection; actin; immune system
Phalloidin (from actin lecture) is similar to ____ (from MT lecture) because it _____.
Taxol; hyperstabilizes actin (doesnt allow it from disassembling)
Cytochalasin infection (actin lecture)?
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)
Diseases related to spectrin?
1. Spherocytosis: pinching off of the RBCs (ankyrin binding domain messed up)
2. Elliptocytosis: RBCs lyse to due messed up spectrin
Two types of muscular dystrophy? Differences?
Duchenne's MD: premature stop codon; actin binding domain mutation
Becker's MD: spacer domain repreats of spectrin
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
The IF subunits are nonpolar or polar, linear or globular?
subunits are linear and polar
IF assembly consists of?
parallel dimers (polar), tetramers (anti-parallel [non-polar] = unit-length filament)
Growing assembly of IF (from subunit to IF)?
Dimer, tetramer, ULF, linear end-on-end addition ofULF (non-polar)
ULF have the intrinsic ability to repair themselves?
Phosphorylation of the head =?
Phorphorylation of the tail =?
- Phosphoryl. of the head = disassembly
- Phosphoryl. of the tail = creation of side arms
Function of tonofilaments?
link cells together to transfer mechanical force
K5 or 14, basal layer mutation leads to epidermolysis bullosa simplex (EBS)
K1, or 10, stratum spinosum mutation leads to epidermolysis hyperkeratosis (EH)
Increased susceptibility to muscle damage (dystrophies)
Lamin A laminopathy?
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