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CMCB Fall > Microtubules #15.2 > Flashcards

Microtubules #15.2 Flashcards

1
Q

Treadmilling in - and + ends of microtubule

A

Critical Concentration (Cc) of minus ends of MTs is greater than that of Cc on plus end

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2
Q

What is dynamic instability?

A

Predominant behavior in MTs

Expalined by fact that minus ends of MTs are often capped and thsu not in a position to participate in treadmilling

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3
Q

When does treadmilling occur?

A

at intermediate concentrations, MTs undergo net assembly at pls end and net disassemby at minus end==> net flux of subunits through polymer

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4
Q

What is Dynamic Instability?

What is catastrophe and rescue?

A

Growing and shrinking of Plus Ends.

Occurs at Plus Ends of MTs

Rapid Disassembly phase called “catastrophe” (sometimes goes to completion)

Sometimes reverses to “rescue” –> assembly contineus

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5
Q

GTP Cap Model of Dynamic Instability

How fast is GTP hydrolysis after assembly

A

GTP hydrolysis occurs in a delayed manner after assembly

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6
Q

What happens if rate of assembly is rapid due to a high concentration of GTP-bound tubulin dimers?

A

If rate of assembly outpaces hydrolysis, a “cap” of GTP-containing subunits covers the + end of the MT

This cap is a STABILIZING force preventing disassemby from that end and enabling futher assembly

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7
Q

What does the “cap” of GTP-containing subunits do?

A

Covers + end –> STABILIIZES MT, preventing disassembly fromt aht end and enabling further assembly

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8
Q

What if assembly is slower due to a low conentration of GTP-bound subunits>

A

GTP hydrolysis will eventually lead to an end with exposed GDP containing tubulin subunits

MT is UNSTABLE and undergoes rapid SHORTENING

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9
Q

What is configuration fo GTP containing protofilments? GDP contianing protofilaments?

A

GTP containing protofilaments are thought to have “straight” configuration

GDP containing filaments have a relaxed, more cured or kinnked confomration that has a destabilizing effect
When kinks occur at the end , unraveling /disassembly of the end occurs

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10
Q

What happens when GDP bound subunits form bends or kinks in the TRUNK or CORE regions of MT?

What happens when they happen near the MT plus end?

A

IF in the core region, bending foreces are counterbalanced by forces of side-to-side binding of tubulin subunits in wall of MT

When kinks and curvatures happen near the MT plus end, they act to separte the protofilametns at the MT end, making shrinking and depolymerization ore likely

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11
Q

Are (-) ends in living cells really dynamic?

A

NO! b/c they are functionally capped by the MTOC (microtubule organizing center) = CENTROSOME

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12
Q

What is the MTOC/Centrosome? Function? What is at the core of MTOC?

A

Organizes the cytoplasmic array of MT in interphase cells.

At the core is a pair of centrioles surrounded by centrosomal matrix (pericentriolar material)

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13
Q

What side (minus or plus) is associated with MTOC?

A

Minus side

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14
Q

What is the cell center of a CENTRIOLE called?

A

CENTROSOME

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15
Q

Describe the structure of a centriole

What is the cell center called?

How many centriole pairs are there?

What is the composition of the centriole? Name whether they are complete or incomplete microubules

A

Centrioles have two halves positioned at right angles to each other at the cell center (centrosome)

Each half contains 9 TRIPLET MICROTOBULES arranged around a hollow core

Each triplet is composed of
Subfiber A (complete microtubule)
Subfiber B & C (incomplete MTs fewer protofilaments)

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16
Q

Describe the structure of CILIA/FLAGELA

A

Doublet Microtubules

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17
Q

What is the structure of each centriole identical to?

A

Stcuture of basal body (structure at the base of the cilia)

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18
Q

What happens when you put centrosome (with centrioles) in vtiro?

A

Centrioles and pericentriolar material that constitute the centrosome protects/caps the minus ends of the MTs and allows assembly to proceed rapidly from teh plus end

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19
Q

What is the drug COLCHICINE?

What happens when COLCHICINE added to MT

A

Colchicine is an antimitotic drug that causes MT to disassemble

Subseqeunt washout of drug allows MT reassembly which initiates at the centrosome/MTOC as a small aster and then expands to regenerate MT array in cell

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20
Q

What is the stuff in centrosome that caps?

A

Higher plants have NO centriole,s yet they have a MTOC

GAMMA TUBULIN (different gene form alpha, beta, doesnt form tubules by ….)

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21
Q

What is GAMMA TUBULIN

A

ring complex –> nucleates and caps (-) end of microtubule

MT grow from the gamma tbulin ring complexes of the centrosome

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22
Q

Wher eis centrosome/MTOC located?

What does it contain?

A

in cytoplasm near the nucleus

IT contains a pair of centrioles and an amorphous matrix that contains MT nucleating material at the centrosome

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23
Q

What is the protein enriched at centrosome which is known to nucleate new MT by binding and stabilizing (-) ends

A

gamma tubulin

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24
Q

How is gamma tubulin different from alpha and beta tubulins that form MTs >

A

Forms unique “ring” structures called gamma tubulin ring complex (gamma-TuRC)

TuRC nucleatures new MTs by presenting a row of gamma tubulin subuints to recruit and bind minus ends

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25
Q

Are gamma tubulin part of centrioles or pericentriolar material?

A

Pericentriolar material

26
Q

What are MAPS

A

Microtubule Associated Proteins

first identified as persistent contamination in teh purification of tubulin by repeated cycles of assembly/disassembly

extremely heat stable

co-localize to MT networks

There are assembly MAPS and motility MAPS

27
Q

What are roles of MAPS (4)

give examples

A
  1. Promoting MT assembly
  2. Stabilizing MTs
  3. Crossbridging or bundling MTs
  4. Mediating interactions of MTs with other cellular polymers or organelles

tau, MAP2

28
Q

Where do TAU and MAP2 localize

What disease is TAU associated with

A

TAU protein is concentrated in axons

MAP2 is concentrated in cell bodies and dendritic region of neurons

Tau forms the insoluble paired helical filaments that are present in Alzheimer’s disease brain tissue

29
Q

Proteins that bind MT + ends can stabilize or destabilize .

What is an example of a protein that can stabilize? What happens and what is the result

What is an example of a protein that can destabilize? What happens and what is the result

A

STABILIZE- MAPS–> frequency of catastrophe sugressed and growth rate enchanced

Result: onger, less dynamic MT

DESTABILIZE: KINESIN
–> frequency of catastrophe increased
RESULT: shorter, more dynamic microtubules

30
Q

What does family of kinesin-related proteins do when they bidn to MT + end?

A

known as CATASTROPHE FACTORES

bind to MT and PRY the protofilaments apart

31
Q

Stability with plus end vs inus end

A

Minus end is very stable b/c it is associated with CENTROSOME

Positive end is unstable b/c it associates with highly dynamic MTs

32
Q

Where does EB1 protein bind?

A

Binds to GTP protein caps at tips of + MT

Stilla llows it to assemble

33
Q

What is Taxol? Is it a stabilizing or destabilizing drug?

A

Binds and STABILIZES MT

used to be used in brease cancer

34
Q

What is Colchicine? Is it a stabilizing or destabilizing drug?

A

binds subunits and PREVENTS POLYMERIZATION- destabilizer

35
Q

what is Vinblastine, vincristine? Is it a stabilizing or destabilizing drug?

A

binds subunits and PREVENTS POLYMERIZATION- destabilizer

36
Q

What is Nocodazole? Is it a stabilizing or destabilizing drug?

A

binds subunits and PREVENTS POLYMERIZATION- destabilizer

37
Q

What are microtubular motor proteins?

A

Involved with cell motillity mechanism that generates energy from ATP

38
Q

What are three main examples of cell motility that utilize MTs

A
  1. Movement of cilia and flagella (Axonemal motors)
  2. Transport of membrane vesciels in the cytoplasm (Cytosolic motors)
  3. Alignment and separation of chromosomes during mitosis and meiosis by action of itotic spindle apparatus (Spindle Motors)
39
Q

What are cilia and where can they be found

A

Cilia are surface projections found on SPECIALIZED EPIthelial cells such as those lining the Respiratory Tract and parts of teh reproductive tracts

Surface cilia move in coordinated waves that are useful in propeling unwanted material (dust/mucus)

40
Q

What allows cilia to move?

A

core of MTs that are responsible for their motility`

41
Q

what are flagella

A

have identical core structure but are longer

42
Q

Wheredoes the motile machinery come from in a Cilia/Flagella?

A

WITHIN THE AXONEME!!! not the base!

43
Q

What happens if you shear cilia and flagella from cell surface? will they still have a whip-like stroke?

A

YES! b/c movement comes form AXONEME not base!

44
Q

What will happen if you remove plamalemma proteyically?

A

Ciilia and Flagella will still beat if ATP is present

45
Q

What is an axoneme?

What is its structure?

A

It is the core of the Cilia and Flagella

It is composed of 9 Doublets and 2 singlets in the center

(9+2) arrangement

46
Q

Describe outer doublet composition of cilia/flagella axoneme

A

Subfiber A is complete MT with 13 protofilaments while B subfiber is incomplete (13 protofilaments)

47
Q

What protein strengthens junction between A and B tubules of an outer doublet ?

A

tektin

runs longituidnally along wall of each outer doublet

48
Q

What are inner and outer arms made ot of?

A

Ciliary dynein protein complex

located at periodic intervals along the lenght of axoneme and extend between the doublet MTs at regular intervals

Dynein arms extend form A subunit to B subunit of next adjacent outer doublet

49
Q

What are crosslinkers that hold axoneme together?

A

links made from protein NEXIN, join outer MT doublets in an elastic strap-like fshion like radioal spokes that extend form inner 2 singlet MTs toward teh outer doublets at regular intervals

50
Q

What are dyneins?

A

minus end directed MT motors

51
Q

What are two major brancehs of dynein family?

A

axonemal or ciliary dyneins

52
Q

What are axonemal dyneins?

A

very large protein assemblies composed of numberous polypeptide chains, including 2 or 3 heavy chains that include motor domains which form the globular dynein “heads”

53
Q

What are axonemal dynein heads? Structure? association with ATP?

A

2 or 3 heavy chains that include motor domains which form the globular dynein heads

heads have ATP-dependent binding site for B-microtubule of an axonemal outer doublet

Tail binds to an A-microtubule in an ATP-independent manner

Head binds B-MT, ATP dependent

Tail binds A-MT, ATP independent`

54
Q

Cytoplasmic Dyneins

Location and function

A

Heavy Chain homodimers, 2 large motor domains as heads

Found in all eukaryotic cel

Improtant for membrane vesicle trafficking on MTs

55
Q

What is the mechanism of ciliary motility?

what expt was used to find this out?

A

Microtubule sliding

isolated axonmeal prepartions stripped of membrane and crosslinking proteins

When ATP was added to such preparations, dyneim arms WALK towards MINUS end of each adjacent doublet using ATP hydrolysis causing teh outer doublets to slide apart

56
Q

how much longer does the structure get after Dynein arm walks towards minus end of MT?

A

9x longer in a telescopic fashion

57
Q

How does each dynein arm geerate force?

A

ATP hydrolysis

58
Q

What happens to dynein arms in teh absence of ATP?

A

dyneim arms become locked

ATP binding dissociates motile partners

59
Q

What is a Basal Body (BB)

A

base of axoneme

60
Q

What is the structure of the BB

A

9-triplet MT that is identical to that in a centriole

A and B tubules of BB continue into and are continous with teh outer doublets of teh axoneme while C tubule ends a the transition zone betwen teh basal body and teh axoneme

61
Q

Function of Basal Body

A

nucleating center for cilia/flagellum

essential for axoneme to reform if cilia/flagella are sheared off from surface of cell

62
Q

What is Kartagener Syndrome (KS)

cause?

PResentation in patients

Symptoms

A

one of the inherite dPrimary Ciliary Dyskinesias

defective, nonproductive cilia that occur b/c of mutations in DYNEIN COMPLEX PROTEINS

KS patients have greatly reduced number of dynein arms or abnormal axonemes that are missing eithe rinner, outer or both dynein arms

Chronic upper and lower resp tract disease sinusistis and bronchitis) resuling from ineffective mucus clearance

Immotile spermatozoa (male sterility)

Sinus Inversus (mirror image flipped organ placement such as the case of dextrocardia) . Occurs in 1/2 the patients

Normal ciliary beating is essential for proper visceral rotation during embryonic development

CMCB Fall (17 decks)

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