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ANAT 262 > Cytoskeleton: Microtubules > Flashcards

Cytoskeleton: Microtubules Flashcards

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1
Q

What is tubulin

A

Gtpase

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2
Q

How are microtubules formed

A

From tubulin subunits
13 straight protofilaments - many flavours

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3
Q

Diameter microtubuels

A

250 angstrom diameter
Hollow tube
Polar filaments - + and neg diff properties

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4
Q

Are microtubules soft

A

NOO
GENerally rigid = 5200um persistant length

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5
Q

What do microtubules attach to

A

Typically attach to a central organizing centre - centrosome

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6
Q

What are microtubules the basis for

A

Larger structures = cilia, flagella

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7
Q

Describe mtoc

A

Where Mt grow and shrink from

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8
Q

Describe drosophila embryo synchronized division

A

Dynamics allow micortubule cytoskeleton to rapidly reorganize during mitosis

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9
Q

Why are microtubules essential

A

Broad range cell functions
Mitosis - chromosome segregation
Transport and organelle position - tracks for molecular motors
Cell shape and polarity -neuronal axon
Cell motility - cilia and flagella (sperm)
Signalling - primary cilia (in many places of bodu)

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10
Q

What makes up microtubule subunit

A

Heterodimer =
Made of
beta (exchangeable gtp site= hydrolysis happens here)
And
alpha tubulin (non exchange gtp site - locked in place, structural role - does not change)

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11
Q

Describe multiple isoforms of tubulin

A

7 alpha genes
7 beta genes
Super conserved bc have many important functions
Differences mainly in a the c term tail end
Mediate interactions with accessory proteins tailored to diff cell types

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12
Q

Describe microtubule assembly interactions

A

Alpha beta tubulin - assembly contacts = forms protofilaments that then interact
Lateral contacts = weaker
Longitudinal contacts = stronger

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13
Q

Describe microtubule assembly interactions Destabilization

A

Lattice destabilized by gtp hydrolysis - on beta subunit
When dynamic instability - mt shrinking and groaning

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14
Q

Describe microtubule assembly interactions- for final microtubule product

A

Alpha-alpha or beta-beta lateral contact except at the seam
Tube fold over itself

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15
Q

Why are weaker lateral interactions important

A

Allow for flexibility

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16
Q

Describe microtubule geometry

A

Typical = 13-3
Only geometry in which protofilaments are straight, has to be straight to make protofilament
Others are bendy bc of hydrolysis happening in microtubule when polymerizing

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17
Q

Do alll microtubule have exactly the same number of protofilaments

A

NOO can have diff numbers
But almost all are 13 protofilaments inside cells

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18
Q

What do actin and tubulin share

A

Polymerization characteristics

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19
Q

Describe polymer growth curve

A

Distinct s shape
Lag phase - nucleation limited, then growth phase, then eq phase
Dimers want to go back to monomers = rate constant high but then no elation= rate constant to make polymer increases
Proteins that help nucleation point are very important

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20
Q

Describe critical concentration

A

Balanced assembly and disassembly = critical concentration
Number of monomers adding to filament = number of monomers coming off
Steady state
Koff/Kon = Cc = 1 = no net polymer growths

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21
Q

Describe filament ends

A

Structurally distinct bc polarity
Minus end = slow growth
At plus end = faster growth
For generally polymers critical concentration same at both ends

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22
Q

Describe gtp binding and hydrolysis

A

Chemically different filament ends - depends on critical concentration
Cc(neg end) > Cc (pos end)
Bc micortubule cap usually at + end

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23
Q

What does ntp binding do

A

Drives polymerization
Increase affinity of subunit for polymer = increase kon(ntp)
Subunits add in ntp state

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24
Q

What does ntp hydrolysis do

A

Drive depolymerization by destabilizing lattice contacts = more likely to come out of polymers
Increase koff (ndp)

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25
Describe dynamic instability - cap
Delay between subunit addition and gtp hydrolysis leads to a gtp cap - growing - means it’s stable and growing Add at faster rate than hydrolysis When subunit addition faster than ntp hydrolysis = polymer grows
26
Describe dynamic instability - disassembly
When hydrolysis catches up = ntp cap lost -= catastrophic disassembly Constantly adding or losing subunits
27
Describe microtubule subunits in solution vs filament state
Straight = in Filament state Curved in solution state, off axis
28
What must subunits do to incorporate into lattice
Subunits must straighten to incorporate into lattice Add gtp tubulin to polymers = have to straighten out Structural explanation for differences in on rates at + and - end In gdp bound state = curved
29
Describe curved vs straight conformation
Generates lattice strain Exchangeable gtp - added to straight protofilament - gtp hydrolysis changes subunit conf = weakens bond so now curved protofilament due to hydrolyzation gtp = microtubule polymerization - catastrophe event Growing = gdp lattice under strain - wants to curved but locked straight Shrinking = loss gtp cap allows gdp protofilaments to relax to curved state and disassemble
30
Describe microtubule catastrophe
Curved protofilaments associates with disassembly Less stable Region of micortubule contains gdp tubulin dimers Once cap gone = splay at end and shrink
31
Describe microtubule rescue
Critical concentration gets High enough so then can state adding back on gtp subunits = growth Regain of gtp cap = recscue
32
What is an inherent property of tubulin
Individual filaments cycle between catastrophe and rescue
33
Name all microtubule interacting proteins
Nucleation and anchoring Sequestration Destabilization Cross linking Stabilization Growth acceleration Adaptors
34
Name the 2 classes of microtubule interacting proteins
Structural maps - microtubule associated proteins Motor proteins - kinesin and dyenin
35
Describe maps
Co purify with tubulin during cyclic assembly/disassembly Binds and stabilizes mts - promotes assembly Ex = map-2, tau (Alzheimer’s) in neurons
36
Describe motor proteins
Convert energy of atp hydrolysis into direction motion along microtubules Kinesin = mostly + end directed Dyenins = minus end directed
37
Describe mtocs
Centrosome = mtoc neg end Nucleating site for mts Ex = animal centrosome = organized by amorphous pericentriolar material - cloud of protein surrounds centrosome Ex = yeast spindle pole body = organized in paracrystalline plaques embedded in nuclear envelope VERY DIFF CELLUALR STRUCTURES - SAME MECHANISM FOR NUCLEATING MTS
38
Describe what nucleates microtubules
Y-TUBULIN complexes HOMOlog of alpha/beta tubulin Y tubulin - small complex 300kda, yTuSC Y tubulin ring complex - yTuRC = 2.2 mda Circulates in peri centriolar space - like lock washers ESSENTIAL FOR NUCLEATION IN ALL EUKARYOTUES
39
Describe nucleation mechanism
YTURC = micortubule template Serves as first ring of tubulin in mt First circle of mt - creates seam - started in ring complex
40
What do yturcs do
Cap and stabilize mt minus end After ncuelation - y turcs stay attached =why Little or no dynamics at - end, and all the activity at + end
41
What will bind + end mt
Gtp cap - on plus end - proteins bind to it to. Stabilize it so can keep growing or destabilize it
42
Describe factors that stabilize + end
Map Suppress catastrophe and growth rate enhanced =long less dynamic mts - improve growth state Tips = tack growing end, enhance growth rate and mediate attachment and stabilization Protein - if attached to growing end and will walk along faster
43
Describe factors that destabilize + end s
Kinesin 13 = catastrophe factor Peels away gtp cap Result = shorter, more dynamic microtubuels
44
Name side binding maps
Katanin and spastin Map2 and tau
45
Describe Katanin and spastin
Sever microtubule in middle = 2 neg ends No gtp in middle = expose 2 gdp ends = depolymerizes fast Bind sides mts and severs them
46
Describe map2 and tau
Bind and cross link mts in neurons
47
Describe motor proteins - what are they
Binding domains attach to cargo Motor domains move along mts Kinesin and dyenin hydrolyze atp to generate energy for movement Direction of movement depends on which motors are bound and active
48
Which direction does dyenin move in
Moves towards neg end - cell body
49
Which direction does kinesin move in
Twoards plus end - axon Terminal (more Like myosin’s)
50
Describe kinesin structure
Cargo binding domains Mt binding and catalytic core (atpase), Motor - feet walking along
51
Describe dyenin Structure
Cargo binding Catalytic core - atpase (AAA atpase), changes positions of feet = walks Mt binding = where feet are and walks along
52
Name and describe families of kinesins
Classified by domain organization Motor head and atp hydrolysis one end, then cargo binding other = kinesin 1 (+ end directed) Kinesin 3 = short (+ end directed) Mt sliding = kinesin 5, binds itself and makes bipolar motor (+ end directed) Kinesin 13 = non motor, binds mt ends and increases dynamic stability Kinesin 14 = neg end directed, wants to go towards that, creates chroms
53
Describe mechanism of kinesin movement
2 feet bind mt Linker - adp unstructured but with atp = thrust forwards Cargo binding domains doesn’t interfere with feet Lagging head = tightly bound, atp bound, Leading head = loosely bound, to adp Hydrolysis on lagging head weakens attachment - trailing foot hydrolysis = becomes weak = neck region flips over and steps right Detachment of lagging head - exchange at leading head thrusts linker arm forwards Lagging head becomes leading head - step then swing then keep walking along Neck region responsible for whipping action of brining adp motor head off microtubule
54
How does kinesin move
Cooridnateion of atpase cycles between heads -causes head over head walking Bc one head is slays bound - motion is very processive - kinesin takes long trip along mt - doesn’t wrap around but walks along
55
Describe dyenin structure - specific s
Huge protein = 500kda Cargo binding domain near tail Mt binding stalk = between 2 aaa domains Completely unrelated to kinesin part of aaa atpase fam of enzymes
56
How does dyenin move along micorubuels
When phosphoryltaed = twists and turns = causes foot to move up during power stroke Rotation fo atpase ring change in linker ring. Contacts Dimerization required for processivity = middle of molecule spins to moev foot When spin = put one foot in front of other
57
Describe large mt assemblies
Related structures with similar organizations Cilia- mt related cores Flagella - long mt in sperm Centrioles - mtoc Basal bodies -derived from centrioles
58
Describe centriole
Core fo centrosome
59
Describe basal body
Anchors cilia/flagella Derived from centriole
60
Describe flagella
Long, whip like motion Sperm motility Not like bacterial flagella
61
Describe cilia
Shorter, wave like motion Primary cilium - signal receptor
62
How do cilia and flagella form
Form bundles of mt doublets 9 + 2 organization Complete a microtubule, b microtubule shares protofilaments from a 2 cargo binding domains Other dyenin arm - can bind cargo portion microtubule Mt binding domain - grabs onto next double and bind them - but cannot move bc linked by nexin so they bend
63
Describe organization of cilia and flagella
Dyenin wants to walk towards minus end Causes mt bending - when power stroke
64
How do centrioles and basal bodies from
Bundles of mt triplets Centrioles - have 3 mts = a (complete), b and c (share - incomplete)
65
Describe mitotic spindle
Mother of all mt assemblies Entire mt network is completely reorganized once per cell cycle Enormous machine for accurate segregation of genome Microtubules excluded from nucleus dispersed throughout cytoplasm in g2
66
Name the 3 classes of microtubules of mitotic spindle
Astral Kinetochore Inter polar
67
Describe astral microtubule - gen
Position within the cell Look for outside of cell - look for poles of cells, grab cortex at poles diving cell - dyenin here
68
Describe kinetochore microtubule - gen
Neg end centrosome Grow and shrinks - finds super chromatids and binds at kinetochore Attachment to chromosomes
69
Describe interpolar microtubule - gen
Growing and skinning Spindle stability Look for other mts - and bind then grab each other - kinesin between them
70
Describe how mitotic spindle sculpted
Motor proteins sculpt spindle Spindle organization results from exquisite balance of forces Forces from both molecular motels and intrinsic mt dynamics
71
What does dyenin do - for mitotic spindle
Pulls poles twoards cortex Astral mt - dyenin grabs cell wall and pulls centrosome back twoards cell
72
What does kinesin14 do - for mitotic spindle
Cross link - pulls poles together
73
What does kinesin5 do - for mitotic spindle
Sliding - push pole apart - want to go to neg end Polar mt = will push a way and slide microtubules apart = pulls centrosome away
74
What does kinesin4,10 do - for mitotic spindle
Move chromosomes to metaphase plate
75
What do kinetochore microtubules do for mitotic spindle
While rest going on = kinetochore micortubules grab dna and pull apart
76
Describe Dynamic tension
Balance of forces to align chromosomes Cut sister chromatids with laser - other arm pushes, arm without kinetochore = more away from pole Arm with kinetochore moves towards pole Push = inter polar or astral micortubule Pull = kinetochore mt Small perturbations to system allow large rapid responses Check point - need all dna to line up at metaphase plate Constant push and pull = to bring dna back towards centrosome, centrosome move back and away from each other
77
Describe attachment of mts to chromosomes
Mts stabilized by interactions with kinetochore Mechanism of kinetochore attachment = inside kinetochore= proteins that like to bind polymers, hook and pull and separate chroms - monomers come off Kinetochore mts grab kinetochore proteins and start to depolymerize - pull dna back = proteins phosphorylated so micortubule depolymerizes and little arms grab to next point Depolymerization slower eand regulated - prevent catastrophe Phopshatase to undo it
78
Describe chromosome separation components
2 components = anaphase a, and anaphase b
79
Describe mt depolarization driven chromosome separation
Anaphase a = movement of chromosomes towards poles Shortening kinetochore microtubuels - movement of daughter chroms to poles, forces generated mainly at kinetochore Polymer short Chroms come apart
80
Describe motor driven chromosome separation
Movement of poles away from each other Walk towards neg end - dyenin mechanism Pulls poles back twoards edge -away from dna Astral mts Sliding force generated between inter polar microtubules from opposite poles to push poels apart, inter polar micortubules also elongate, pulling force acts directly on the poels to move them apart
81
what does brain have
Lots of microtubules = need to be cold, fall apart at 40 degrees - disassemble
82
What does taxol do
Binds lattice micotubuels and stops growth

ANAT 262 (24 decks)

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