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BIO 2600 > Chapter 17 > Flashcards

Chapter 17 Flashcards

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1
Q

Three types of cytoskeleton filaments, widest to thinnest

A

Microtubules, Intermediate filaments, and Actin

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2
Q

Intermediate filaments function and properties

A

withstands mechanical stress of stretching
high tensile strength (deform but don’t break)
distribute strength among tissue cells through desmosomes
form nuclear lamina/extend through cytoplasm

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3
Q

Intermediate filament structure

A

monomers contain central rod domain and unstructured regions at both ends
rod domains (a-helical) join to form coiled coil dimer
staggered antiparallel tetramer of two dimers
lateral association of 8 tetramers add together to form filament
NO STRUCTURAL POLARITY
unstructured regions vary and are exposed on the outside of filament

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4
Q

cytoplasmic intermediate filaments

A

keratin (epithelial cells) - most diverse
vimentin/vimentin-related (connective tissue, muscle, glial cells)
neurofilaments (nerve cells)

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5
Q

nuclear intermediate filament

A

nuclear lamins form nuclear lamina
NOT rope-like, mesh-like

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6
Q

mutations in keratin cause what

A

skin more prone to blistering, even with gentle impact- epidermolysis simplex

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7
Q

mutations in neurofilaments cause . . .

A

ALS; Amyotrophic lateral sclerosis

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8
Q

nuclear lamina

A

meshwork of IF beneath nuclear envelope
attachment sites for chromatin
comprised of lamin proteins
help position chromosomes

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9
Q

defects in nuclear lamina cause . . .

A

progeria; rare class of premature aging disorders due to nuclear instability, leading to defects in cell division and chromosomal positioning

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10
Q

how is the nuclear lamina regulated by phosphorylation for disassembly/reassembly for cell division

A

phosphorylation by kinases weakens interactions between tetramers
dephosphorylation by phosphatases strengthens and rebuilds

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11
Q

function of nuclear lamina in connecting nucleus to cytosol and examples

A

Accessory proteins in membrane crosslink IFs to other cytoskeletal components outside the nucleus
Plectins: cytosolic bundling of IFs, connects nuclear lamina to cytosolic components
SUN and KASH: transmembrane proteins, link nucleus to cytoplasm, nuclear positioning

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12
Q

microtubules monomers

A

tubulin dimers made of alpha and beta tubulin, held together by noncovalent bonds

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13
Q

function of centrosomes

A

microtubule organizing center (MTOC) from which microtubules grow and extend out to the rest of the cell

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14
Q

main functions of microtubules

A

guide transport of vesicles, organelles, and other cell components
form mitotic spindle during cell division
found in flagella and cilia

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15
Q

which tubulin subunit is plus end/minus end

A

alpha = minus end
beta = plus end

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16
Q

tubulin monomer assembly into filaments

A

linear protofilament of dimers
13 protofilaments form microtubule all oriented in same direction (structural polarity)

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17
Q

tubulins easily add to which end of the MT filament

A

plus end

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18
Q

centrosomes structure

A

two centrioles surrounded by protein matrix

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19
Q

gamma tubulin location and function

A

rings found in centrosomes that serve as nucleation sites foe MT filaments
dimers add to gamma ring

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20
Q

which end of the MT filament is embedded in the centrosome and which ends extends into cytoplasm

A

minus ends embedded in centrosome
growth occurs at plus ends in cytoplasm

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21
Q

dynamic instability

A

each MT filament is constantly growing and shrinking independent of neighboring filaments due to GTP hydrolysis

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22
Q

requirements for a formed microtubule to persist instead of rapid disassembly

A

both ends protected from depolymerization
MINUS ends protected by organizing centers
PLUS ends stabilized by capping proteins
SELECTIVE STABILIZATION

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23
Q

when are MTs more stable/less stabel

A

more stable in polarized and differentiated cells (nerve cells)
less stable in dividing cells

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24
Q

which way to MT filaments all point to create structural polarity in neurons

A

plus end toward axon terminal

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25
function of motor proteins
intracellular transport; bind to MTs and cargo (directly or via adaptors)
26
which direction to kinesins and dyneins move
kinesins move toward + end dyneins move toward - end
27
How does ATP hydrolysis cause movement of motor proteins
ATP hydrolysis Pi release loosens attachment of rear motor head to MTs ATP binding to front motor head changes conformation flipping rear motor head to the front
28
kinesins and dyneins structure
dimers of globular ATP binding head and tail
29
kinesins attach to which organelle
ER membrane (via receptor proteins) pull it outward to maintain ER network
30
dyneins attach to which organelle
attach to Golgi and pull it inward keeps it close to nucleus
31
cilia and flagella MT structure
9 + 2 array 9 dimers around outside of tube, 2 in center
32
mechanism of cilia and flagella movement
created by bending microtubule ciliary dynein attached to adjacent microtubules to generate sliding force (ATP) flexible protein links convert sliding motion to bending motion
33
when does the growing MT begin to shrink
when GTP hydrolysis catches up to growing end (GTP cap lost) and GDP bound tubulin has lesser affinity for binding so filament rapidly disassembles
34
what type of tubulin is added to growing end of MT
GTP bound tubulin added to growing MT, high affinity for one another
35
actin filaments main function
modify cell shape during division form contractile ring cell movements of protists/neutrophils
36
Actin filament location
found in bundles more than individual filaments; throughout cytoplasm concentrated in cell cortex
37
Actin structure and characteristics
long thin and flexible 2 twisting strands of actin globular monomer contains plus and minus end (POLARITY)
38
actin treadmilling
ATP-acting added to plus end and ADP-actin falls off minus end at same rate
39
actin-monomer binding proteins example
formin, ARP complex, monomer sequestering protein
40
actin filament binding proteins examples
severing protein, cross-linking (cortex), capping, side-binding (tropomyosin), motor protein, bundling (in filopodia)
41
the leading edge of cell movement process
driven by actin polymerization lamellipodia and filopodia stretch forward with plus ends pointing towards PM
42
lamellipodia
flat sheet-like dense meshwork of actin
43
filopodia
thin stiff loose bundle of actin
44
where is the nucleation complex for actin filaments
growing edge (plus end) of filaments
45
function of ARPs in formation of lamellipodia
branched actin filaments grow from ARPs on existing filaments; plus ends protected by capping filaments
46
function of formin
promotes formation of unbranched filaments - filopodia
47
3 steps of cell movement forward
protrusion attachment traction
48
protrusion
actin polymerization at leading edge pushes PM forward and forms new actin cortex
49
attachment
new anchorage points made between actin and surface on which cell is crawling -integrins anchoring proteins
50
traction
contraction at rear of cell draws body forward, old anchorage points at back released -myosin motor proteins
51
Actin binding proteins respond to extracelullar signals and control actin filaments through . . .
surface receptors that activate signaling pathways which converge on Rho GTPases (molecular switches by GTP hydrolyzation)
52
myosin I
actin dependent motor protein found in all cell types one head domain (actin) and one tail (varies) ATP driven travels minus to plus end
53
myosin II
actin dependent motor protein mainly in muscle cells 2 heads and coiled coil tail tails associate to form filaments bipolar-heads extend in dif directions travels minus to plus
54
which part of myosin II interacts with actin to slide actin filaments over each other
heads; this causes muscle contraction and contractile ring during cell division
55
skeletal muscles makeup
striated appearance made of numerous, very long multinucleated cells (aka muscle fibers) that contain numerous myofibrils
56
myofibril structure
chain of sarcomeres
57
sarcomere structure
two Z discs attached to actin filments (thin) at plus end actin filaments attached to central specialized myosin II filaments (thick)
58
why do muscles contract
synchronized sarcomere shortening actin and myosin slide past each other because of myosin heads walking toward plus ends
59
why do muscle cells relax
myosin heads release actin filaments and sarcomeres lengthen again
60
how do muscle cells respond to signals to contract
action potential spreads to myofibrils via T tubules (extensions of the PM into the cell) T tubules open voltage-gated Ca+2 channels, which also mechanically opens sarcoplasmic reticulum Ca+2 channels increased Ca+2 within the cell binds to troponin and induces conformational change troponin change causes tropomyosin to not block myosin binding sites on actin anymore and initiate contraction
61
what happens to the Ca+2 after elctrical signal passes to relax cells
Ca+2 pumped back into sarcoplasmic reticulum
62
process of myosin moving along actin
1. myosin w/no ATP or ADP bound tightly to actin 2. ATP binds and myosin detaches from actin 3. ATP hydrolysis causes a conformational change in myosin so displaced along actin filament (ADP and Pi attached to myosin still 4. ADP-bound myosin weakly binds to new actin site, causing release of Pi and return to original conformation 5. myosin loses ADP and tightly binds to new region of actin

BIO 2600 (15 decks)

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