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65 Cards in this Set
- Front
- Back
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What are the 3 different types of cytoskeleton? What are each made of?
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Microfilaments - actin
Intermediate filaments - various proteins Microtubules - tubules They are made of repeating subunits of actin/proteins/tubules |
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What kind of forces can the different types of cytoskeleton resist?
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MTs - can resist shear forces
IMFs, MFs - can resist tension forces |
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What are 4 functions of cytoskeleton?
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- determine cell shape/polarity
- intracellular transport - cell movement and ciliary movement - cell division |
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Describe the structure of tubulin.
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Dimer of alpha and beta subunit
Globular protein tubulin dimer is polar bound to GTP |
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How much of total soluble brain protein is tubulin?
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10-20%
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How is tubulin arranged into MTs?
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Dimers align head to tail, forming protofilaments
~13 protofilaments align laterally |
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Describe MT polarity
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Beta tubulin end = Plus end (fast assembly/disassembly) - peripheral/basolateral cell
minus end - slower exchange - at MTOC/apex cell reaches equilibrium |
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What initiates a MT?
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Microtubule organization center (MTOC) (aka centrosome) initiates nucleation
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describe the structure of the MTOC (MT organizing center)/centrosome
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centrioles + Amorphous cloud + gamma-tubulin critical protein (MTS grow from this)
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Describe the dynamic instability of MTs
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GTP tubulin added to plus end
GTP hydrolyzes into GDP GDP tubulin is unstable loses GTP cap - induces disassembly (catastrophy) (weakens bonds, depolymerizes) |
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How does an MT grow? shrink?
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grow: GTP tubulin adds at the end
shrink: GDP tubulin released into cytosol |
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What are the 5 configurations/types of MTs?
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1. Cytoplasmic MT - single MT radiating from MTOC
2. centrioles, basal bodies - short structure made of 9 triplet MT 3. Axonemal (ciliary and flagellar) MT - 9 doublet + 2 singlet MT 4. Neuronal - axonal, dendritic (type of cytoplasmic MT) 5. Mitotic spindle - |
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How does an MT grow? shrink?
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grow: GTP tubulin adds at the end
shrink: GDP tubulin released into cytosol |
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What are the 5 configurations/types of MTs?
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1. Cytoplasmic MT - single MT radiating from MTOC
2. centrioles, basal bodies - short structure made of 9 triplet MT 3. Axonemal (ciliary and flagellar) MT - 9 doublet + 2 singlet MT 4. Neuronal - axonal, dendritic (type of cytoplasmic MT) 5. Mitotic spindle - |
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What is the half life of MTs?
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- cytoplasmic MTs: 10 mins (v. short! v. dynamic/unstable!) - about 20% of the MTS are more resistent to depolymerization
- Mitotic spindle - VERY unstable (half life = 15 secs) until capped - neuronal mt - partly stabilized - Axonemal, basal bodies, centrioles = stabilized |
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What are post-translational modifications of MTs?
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Associated with longevity
- MAPs - (MT assoc proteins) |
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What is the main function of MAPs?
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To be stabilizers
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Give 2 examples of MAPs, state their locations
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Tau - axonal
MAP 2 - dendrites, soma |
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What does phosphorylation of MAPs do?
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reduces affinity for MT, reduces stability.
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What is one hypothesized defect in Alzheimer's disease?
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Hyperphosphorylation of tau
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What does colchicine do?
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MT poison
binds 1:1 with tubulin dimer, blocks further addition net result: disassembly |
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What do vinca alkaloids do/
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binds ends of MTs and dimers, precipitates tubulin, eleminated from assembly
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What is taxol?
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binds to tubulin, hyperstabilization of MTs
induces assembly of dimers |
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When you do chemotherapy, what do you use so as not to disturb other things (ie. GI epithelial cells, blod cell mitosis, intracellular transport in neurons) --> side effects?
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titer agents - to destroy cancer w/o side effects
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What are the two types of motor proteins in intracellular transport?
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Kinesins
Dyneins |
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What is the structure of kinesin?
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Motor domain - globular head
Tail domain - binding cargo most are plus end directed (N terminal motor domain) |
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What are catastrophins?
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kinesins that disassemble MTs (have internal motor domain)
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What is the structure of dyneins?
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minus end directed
globular protein head short shafts multiple units form tails |
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What is the dynactin complex?
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ie. dyneine activator complex
accessory proteins that bind to dyneine, help in transport |
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Name 3 causes of mutations of toxic inhibitions of kinesins.\
Name 3 things that this can lead to |
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organic solvent organophosphate pesticides neurodegenerative disease, reproductive failure, cancer |
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Do the following organelles have kinesin, dynein, or both?
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Membrane bound organelles (ie. vesicles, mito, etc.) -both
ER - Kinesin Golgi - dynein Chromosomes, other elements at mitosis/meiosis - both MT-dep intermediate filaments - kinesin |
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What category are kinesin,dyneine in?
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MAPs
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What is the ciliary function?
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to move fluid or propel cells through fluid
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What are 2 places where you can find?
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Respiratory and reproductive tracts
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Describe the movement of cilia.
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Stiff power stroke
loose, rolling return stroke. |
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Describe the structure of a cilia
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9 outer doublet MTs, 1 pair of MTs in the center
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how many accessory proteins for cilia are there?
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200
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Name 2 important cilia accessory proteins.
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Nexin - flexible protein that links the outer doublets
Radial spokes - connects outer doublets to inner sheath |
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What is ciliary dynein?
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2-3 globular heads with stalks and numerous base proteins. attached to A MT, moves along B MT (+ to -)
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What is the purpose of cross linker proteins between MTs?
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To allow for bending (rather than MTs sliding past each other)
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What causes immotile cilia syndrome (Kartagener's)? What symptoms does it lead to?
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1. Absence of dynein arms
2. Respiratory infections and immotile sperm (male infertility) |
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What 3 kinds of MTs are there in mitosis?
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Kinetochore
Polar MTs Astral MTs |
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What happens during the conversion of interphase MTs to mitotic spindle?
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During S phase, the replicated centrosomes separate.
Nucleation of MT increases, disassembly of MT at the centrosome also increases --> so rate of dynamic instabiility increases over 20fold |
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How is the mitotic spindle assembled?
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Minus end kinesins align mitotic MTs
Kinesins separate centrosomes. MTs extend across length of cell. Dyneines pull centrosomes apart |
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What happens during metaphase?
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Kinetochore captures chromosomes.
one kinetochore captures kinetochore on the opposite side. tug of war aligns chromosmes equidistant from the poles. Involves dynamic MT and motor proteins |
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What happens during anaphase?
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Anaphase A
Disassembly of kinetochore MT as chromosomes move apart Motor proteins maintain attachment Anaphase B: Kinesins slide apart of polar MTs PM bound dyneines pull aster MTs |
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What happens to membranous organelles during mitosis?
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They are equally distributed along MTs to daughter cells.
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Summarize the aspects of meiosis/mitosis that MTs/motor proteins are involved in?
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- spindle formation and maintenance
- chromosome attachment, alignment, separaton - organelle distribution - spindle dissolution |
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What effects could drugs/toxicants have on MTs?
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Bad - uneven distribution of chromosomes; aneuploidy, cancer, inheritable diseases in germ cells
Good - locks cell in mitosis --> apoptosis (used as chemotherapy) |
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What are thick filaments?
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Specific to muscle.
Between IFs and MTs in size |
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What's the difference between MF/MT and IF subunits?
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MF/MT subunits are globular (actin/tubulin)
IF subunits are filamentous |
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What is an associated protein of MFs?
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Myosin - myosin motor can walk on MF scaffolds
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Microfilaments can form what?
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3D structural scaffolds
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What are 2 things implicated in defective MT-regulated cell movement?
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Kartagener's syndrome
Male infertility |
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Is GTP, GDP tubulin bent or straight?
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GTP - straight
GDP tubulin - bent - b/c depolymerizing (GTP hydrolysis changes subunit conformation, polymer bonds are weakened) |
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Describe the nature of assembly and disassembly of MTs
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slow assembly
catastrophic disassembly half life = 10 mins |
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What is GDP tubulin like?
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less compact, thermodynamically unstable -->, therefore induces disassembly
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The critical factor in growing the length of MTs is:
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GTP in beta tubulin
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Give examples of an MT doublet, MT triplets
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MT doublet - axoneme (cilia, flagella)
MT triplet - centrioles, basal bodies |
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Where are the following nucleated?
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cilia, flagella - nucleated at basal body
axons - no known MTOC |
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What is the polarity of mitotic spindles?
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minus ends at the poles
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How is post-translational modification of MTs related with MT longevity?
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-associated (but not cause of longevity!)
- may attract MAPs |
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What effect do MAPs have on MT stability?
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Increase stability
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What effect does phosphorylation have on MT stability?
What does this have to do with Alzheimer's? |
Decreases MT stability
Maybe alzheimers is caused by hyperphosphorylation of MTs? |
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What are the two major types of dyneins?
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Axosomal dyneine
cytoplasmic dyneine |
