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Cell Biology > ch 13 cytoskeletal systems > Flashcards

ch 13 cytoskeletal systems Flashcards

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1
Q

cytoskeleton

A

3D interconnected network of microtubules, microfilaments, and intermediate filaments extending through the cytosol

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2
Q

3 main functions of cytoskeleton

A

1 cell’s distinctive shape and internal organization
2 cell movement and cell division
3 positioning and moving organelles/macromolecules within the cell
additionally - can interact with motor proteins to produce motility (vesicles can travel along ‘monorails’ provided by the cytoskeleton

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3
Q

microtubules

A

the thickest of the 3
consist of tubulin subunits
functions:
cytosolic - organization and maintenance of animal cell shape and polarity, chromosome movements, intracellular transport/trafficking, and movement of organelles
axonemal - cell motility

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4
Q

microfilaments

A

also called actin filaments
the thinnest of the 3
functions:
- muscle contractions
- cell locomotion
- cytoplasmic streaming
- cytokinesis
- maintenance of animal cell shape
- intracellular transport/trafficking

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5
Q

intermediate filaments

A

fibers with diameters in a middle range
often tissue specific ie keratin
functions:
- structural support
- maintenance of animal cell shape
- formation of nuclear lamina and scaffolding
- strengthening of nerve cell axons
- keeping myofibrils in register

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6
Q

septins

A

‘fourth cytoskeleton’
closely associated with the contractile ring, a structure involved in the pinching off of daughter cells during cell division

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7
Q

bacterial and archaeal systems that function similarly to eukaryotic cytoskeletal elements

A

MreB - actin-like, protein forms microfilaments and is involved in DNA segregation and cell shape
FtsZ - tubulin-like, protein is involved in regulating division
Crescentin - intermediate-like, regulator of cell shape

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8
Q

cytosolic microtubules

A

spread through the cytosol
singlets
responsible for:
- maintaining axons
- formation of mitotic and meiotic spindles
- maintaining or altering cell shape
- placement and movement of vesicles

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9
Q

axonemal microtubules

A

organized and stable microtubules found in the structures such as cilia, flagella, basal bodies to which cilia and flagella attach
doublet or triplets

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10
Q

structure of microtubules

A

straight, hollow cylinders of varied length that consist of (usually 13) protofilaments - longitudinal arrays of polymers of tubulin with inherent polarity

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11
Q

basic subunit of a protofilament

A

heterodimer of tubulin: one alpha-tubulin and one beta-tubulin
these bind noncovalently to form an alpha beta - heterodimer, which does not normally dissociate

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12
Q

formation of MTs

A

form by the reversible polymerization of tubulin dimers in the presence of GTP and Mg2+
dimers aggregate into oligomers, which serve as ‘seeds’ from which new MTs grow (nucleation)
once a MT has been nucleated, it grows by addition of subunits at either end (elongation)

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13
Q

MT assembly

A

formation is slow at first bc the process of nucleation is slow - lag phase
elongation phase in much faster
when the mass of MTs reaches a point where the amount of free tubulin is diminished, the assembly is balanced by disassembly - plateau phase

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14
Q

critical concentration

A

concentration at which the rate of assembly of cytoskeletal protein subunits into a polymer is exactly balanced with the rate of disassembly
when tubulin conc exceeds cc - mt growth
when tubulin conc is less than cc - mt depolymerize

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15
Q

two ends of mt

A

plus end - rapidly growing side
minus end

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16
Q

treadmilling

A

addition of subunits at the plus end and removal from the minus end
occurs bc plus and minus ends have different critical concentrations

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17
Q

colchicine

A
  • plant-derived drug that binds to tubulin and prevents its polymerization into microtubules
  • binds to beta-subunit of tubulin heterodimers
  • destabilizes the mt and promotes disassembly
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18
Q

nocodazole

A

synthetic drug that inhibits microtubule assembly; frequently used instead of colchicine bc its effects are more readily reversible when the drug is removed

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19
Q

antimitotic drugs

A

interfere with spindle assembly and thus inhibit cell division
- useful for cancer treatment (vinblastine, vincristine) bc caner cells are rapidly dividing and susceptible to drugs that inhibit mitosis

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20
Q

paclitaxel/taxol

A

drug that binds tightly to microtubules and stabilized them, causing much of the free tubulin in the cell to assemble into microtubules
- causes dividing cells to arrest during mitosis
- used for cancer treatment

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21
Q

mechanism of action of taxol

A

binds to the beta subunit and prevents microtubule disassembly
decreases the critical concentration for tubulin assembly, increases the polymerization rate and stabilizes microtubules
interference with microtubules prevents chromosome separation during mitosis which leads to cell death via apoptosis

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22
Q

GTP role in instability of microtubules

A

each tubulin heterodimer binds two GTP molecules; alpha-tubulin binds one, and beta-tubulin binds a second
the GTP bound to the beta-subunit is hydrolyzed to GDP after the heterodimer is added to the MT
GTP is needed to promote heterodimer interactions and addition to MT, but its hydrolysis is not required for MT assembly

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23
Q

dynamic instability model

A

model for microtubule behavior that presumes two population of microtubules, one growing in length by continued polymerization at their plus ends and the other shrinking in length by depolymerization
growing MTs have GTP at the plus ends
shrinking MTs have GDP

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24
Q

GTP cap

A

at the plus end the provides a stable MT tip to which further dimers can be added and prevents subunit removal

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25
microtubule catastrophe
a switch from growth to shrinkage
26
microtubule rescue
a sudden switch back to growth from skrinkage
27
microtubule-organizing center (MTOC)
structure that initiates the assembly of microtubules ex. centrosome in animal cells the centrosome is associated with 2 centrioles MTs grow outward from the MTOC with a fixed polarity - the minus ends are anchored in the MTOC, growth and shrinkage occurs at eh plus end
28
kinesin transports vesicles
in an anterograde direction
29
dynein transports vesicles
in a retrograde direction
30
microfilaments
form connections with the plasma membrane to affect movement (cell migration and cytoplasmic streaming), produce the cleavage furrow in cell division, contribute to cell shape, associated with myosin in muscle, form a network called the cell cortex inside the cell
31
cell cortex
just beneath the plasma membrane, has actin crosslinked into a loose mech (anchorage)
32
actin
principal protein of the microfilaments found in the cytoskeleton of nonmuscle cells and in the thin filaments of skeletal muscle; synthesized as a U-shpaed globular monomer (g-actin) that polymerize into long, linear, helical filaments (F-actin)
33
polarity of microfilaments
plus end has more rapid addition or loss of G-actin than the minus end
34
cytochalasins
fungal metabolites (derived from molds) that prevent the addition of new monomers to existing MF filaments eventually depolymerize
35
latrunculin A
a toxin from the Red Sea sponge sequesters actin monomers and prevents their addition to MF
36
phalloidin
stabilizes MFs and prevents their depolymerization
37
2 main groups of actins
1 muscle-specific actins (alpha-actins) 2 nonmuscle actins (beta- and gamma-actins)
38
G-actin
like tubulin dimers can polymerize reversibly into filaments with a lag phase (nucleation) and elongation phase similar to tubulin assembly
39
F-actin
composed of two linear strands of polymerized G-actin would into a helix
40
lamellipodia
have a branched network of actin
41
filopodia
polarized 'cables' with the plus end towards the tip of the protrusion
42
stress fibers
relatively thick and stable bundles of actin stretch from the tail of the cell to the front cells that adhere tightly to the underlying substratum have these stress fibers
43
microvilli
have actin bundles - core of a microvillus consists of a tight bundle of microfilaments with the plus ends pointed towards the tip
44
actin binding proteins
proteins that bind to actin microfilaments, thereby regulating the length or assembly of microfilaments or mediating their association with each other or with other cellular structures control occurs at the nucleation, elongation, and severing of MF
45
proteins that regulate polymerization
profilin - competes with thymosin beta4 for G-actin binding, but does not sequester G-actin ADF/cofilin - binds ADP-G-actin and F-actin and is thought to increase turnover of ADP-actin at the minus end of MF, also severs filaments, creating new plus ends in the process
46
capping proteins
protein that binds to the end of an actin filament, thereby preventing the further addition or loss of subunits capZ - binds to plus ends to prevent addition of subunits tropomodulins - bind to minus ends preventing loss of subunits
47
filamin
long molecule consisting of two identical polypeptides joined head to head, with an actin-binding site at each tail act to 'splice', joining two MFs together where they intersect
48
gelsolin
breaks actin MFs and caps the newly exposed plus ends, preventing further polymerization
49
proteins that bundle actin filaments
alpha-actin - protein that is prominent within structures known as focal contacts and focal adhesions, which are required for cell to make adhesive connections to the extracellular matrix as they migrate fascin - found in filopodia, keeps the actin within the core of a filopodium tightly bundled
50
crosslinks
MFs are connected to the plasma membrane by crosslinks made of myosin I and calmodulin MFs in the bundle are tightly bound together by crosslinking proteins fimbrin and villin
51
terminal web
dense network of spectrin and myosin molecules located at the base of microvillus
52
proteins that link actin to membranes
band 4.1, ezrin, radixin, moesin, spectrin, ankyrin MFs are connected to the plasma membrane and exert force on it during cell movement or cytokinesis this connection to the membrane requires one or more linking proteins
53
Arp2/3 complex
complex of actin-related proteins that allows actin monomers to polymerize as new 'branches' on the sides of existing microfilaments activated by a family or proteins that includes WASP and WAVE/Scar
54
formin
a protein involved in actin polymerization that associates with the fast-growing end (barbed end) of actin filaments and can remain at the tip of the growing filament as it elongates
55
inositol phospholipids
type of membrane phospholipid that regulates actin assembly PIP2 can bind to profilin, CapZ, and proteins such as ezrin, recruits these proteins to the membrane and regulates their interactions with actin CapZ binds tightly to PIP2 resulting in its removal from the end of an MF, promoting disassembly
56
Rho GTPases
a family of monomeric G-proteins that stimulate formation of various actin-containing structure within cells key family members: Rho, Rac, Cdc42
57
regulation of Rho GTPases
Rho GTPases are stimulated by guanine-nucleotide exchange factors (GEFs) through the exchange of bound GDP for GTP GTPases activating proteins (GAPs) inactivate Rho GTPases by causing them to hydrolyze their bound GTPs to GDP guanine-nucleotide dissociation inhibitors (GDIs) sequester inactive Rho GTPases in the cytosol
58
intermediate filament
abundant in many animal cells but not found in cytosol of plant cells most stable and least soluble component of the cytoskeleton
59
Class I and II
I - acidic keratins II - basic or neutral keratins found in epithelial cells covering the body and lining its cavities function: mechanical strength
60
class III
vimentin (connective tissue in fibroblasts) desmin (muscle cells) glial fibrillary acidic protein (GFAP) (glial cell and astrocytes) functions: maintenance of cell shape, structural support for contractile machinery
61
class IV
neurofilament proteins found in central and peripheral nerves function: axon strength/size
62
class V
nuclear lamins A, B, and C that form a network along the inner surface of the nuclear membrane function: form a nuclear scaffold to give shape to nucleus
63
class VI
nestin, the substance that makes up the neurofilaments in nerve cells of embryos function: unknown
64
intermediate filament typing
different tissues can be distinguished on the basis of the IF present, as determined by immunofluorescence microscopy important diagnostic tool in medicine to determine the tissue/organ from where cancer originated
65
IF assembly
fundamental subunits are dimers fibrous rather than globular N- and C- terminal domains basic structural unit consists of two IF polypeptides intertwined into a coiled coil two such dimers align laterally to form a tetrameric protofilament protofilaments overlap to build up a filamentous structure about eight protofilaments thick
66
plectin
linker proteins that connect IFs, MFs, and MTs

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