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C Bio > Lecture 26 - Cytoskeleton Part III: Intermediate Filaments & Microfilaments > Flashcards

Lecture 26 - Cytoskeleton Part III: Intermediate Filaments & Microfilaments Flashcards

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Biology 101 flashcards
1
Q

what cytoskeleton fiber has the strongest tensile strength?

A

intermediate filament

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2
Q

where are intermediate fibers the most abundant?

A

cells that endure physical stresses

muscle cells

neurons

epithelial cells

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3
Q

how do intermediate fibers connect to other components of the cytoskeleton?

A

with cross-linking PROs such as plectin

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4
Q

how many diff classes of intermediate filaments are there?

A

6

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5
Q

how many human genes code for intermediate filaments?

A

60

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6
Q

what is the biggest diff b/w intermediate filaments, MTs & microfilaments?

A

intermediate filaments have many diff types whereas, MTs & microfilaments don’t

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7
Q

describe the IF structure

A

IF have a monomer composed of an alpha helical domain with a globular domain at each end (one at the amino end & one at the carboxyl end)

2 monomers come to together where their subunits are parallel to each other

Dimers come together & are aligned in opp orientations

Tetramers aggregate together to form IFs

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8
Q

how do IFs differ in structure from other fibers?

A

no polarity (not + & - ends)

new fibers can be inserted at the ends as well as in the middle

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9
Q

what is the function of an IF?

A

Main function: mechanical support or strength

Hair, fingernails & skin are composed of keratin IFs

Nuclear lamina is composed of IFs, line the inside of the nuclear envelope
Important for the integrity of the nucleus
Progeria has an irregular shaped nucleus b/w of the defect in nuclear lamina PROs

Neurons composed of neurofilaments

Cancer diagnostics – keratin have
subtypes that are unique to diff epithelial cells or subtypes for diff cell types
Antibodies bind to keratin
Determines origin of tumour

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10
Q

what are the 2 types of junctions that IFs form?

A

desmosomes - keratin IFs form junctions that hold cells together

hemidesmosomes - attach cells to the matrix

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11
Q

what cytoskeleton fiber is the thinnest of all fibers?

A

microfilaments

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12
Q

what are microfilaments composed of?

A

actin

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13
Q

MT are composed of _____

Microfilaments are composed of _____

IFs are composed of _____

A

tubulin

actin

diversity of PROs

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14
Q

what is required for an actin subunit to become apart of a growing filament?

A

ATP

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15
Q

do microfilaments have a polarity?

A

yes b/c the actin monomer has a polarity

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16
Q

when is ATP on a microfilament hydrolyzed?

A

once actin is part of the microfilament

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17
Q

what are the functions of actin filaments?

A

form a band just beneath the PM to provide mechanical strength

Links transmembrane PROs to cytoplasmic PROs, repositions receptors on PM

Anchors centrosomes to poles

divides the cell during cytokinesis

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18
Q

what cytoskeleton fiber is responsible for cytoplasmic streaming?

A

microfilaments

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19
Q

what cytoskeleton fiber generates locomotion in white blood cells & the amoeba?

A

microfilaments

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20
Q

what cytoskeleton fiber is reponsible for the force generate in muscle contractions?

A

microfilaments (interacts with myosin filaments)

21
Q

myosin

A

motor PROs that move along actin filaments, while hydrolyzing ATP

22
Q

what type of myosin is found in skeletal muscles?

A

myosin II

23
Q

describe how microfilaments assemble

A

actin subunits are added to growing filaments, actin subunits require a bound ATP in order to polymerize with the chain. Once polymerized the ATP is hydrolyzed

Added to ends of the growing chain

24
Q

describe myosin II structure

A

2 heavy chains

Each chain has a globular motor domain that includes 2 domains for:
ATP binding site
Interaction with actin

25
Q

what is the role of myosin V?

A

intracellular transport

26
Q

myosin V structure

A

2 heavy chains

Longer neck region than myosin II - enables long strides

Contain cargo binding domains

27
Q

rigor

A

ADP dissociation leaves the myosin head tightly bound to actin, in the absence of ATP this state results in muscle rigidity

28
Q

when does rigor occur?

A

when ATP & ADP have not been produced enough

29
Q

when does ATP hydrolysis occur in myosin?

A

everytime a myosin head moves

30
Q

what does ATP hydrolysis in myosin cause?

A

movement of the neck region, to get the heads to walk

ATP helps secure a spot on the actin & its hydrolysis causes the head to move

31
Q

Myosin V attaches to every ____ actin residue & only walks along ____ of the filament

A

13th

one side

32
Q

what facilitates myosin V to take long strides?

A

the long neck region

33
Q

when do the microfilaments form extensions?

A

when ingesting a cell during phagocytosis

cell movement

34
Q

lamellipodia

A

growing actin filaments facilitating cell movement

35
Q

what cells use lamellipodia?

A

cells capable of movement without cilia or flagella

36
Q

what is myosin’s role in lamellipodia? & how does it do this?

A

pull rest of the cella long during cell movement

by attaching to other cell components

37
Q

where is myosin located in a lamellipodia?

A

in a band behind the actin

38
Q

how do lamellipodia form?

A

the initiation of actin polymerization by the addition of actin monomers at the PM

39
Q

what controls the polymerization of lamellipodia?

A

actin binding PRO complexes

depolymerization occurs at the base of the lamellipodium

40
Q

how is the actin network size effected by lamellipodia?

A

remains the same size

41
Q

Dictyostelium

A

soil living amoeba

42
Q

What occurs when Dictyostelium have a limited food reserve?

A

will aggregate to form a multicellular assembly called a pseudoplasmodium or slug

they move together on mass & go to the top of the soil where they create a stalk

they form a FB to produce spores where new spores are carried off to find new food reserves & the cells in the stalk die

43
Q

how does Dictyostelium seek out each other?

A

using chemoreceptors

one being cAMP receptor

44
Q

what molecule is required for the polymerization of the actin network?

A

Ca2+

45
Q

what are the steps in cAMP-mediated Dictyostelium movement?

A

cAMP reception at the PM activates GPRO

G PRO stimulates adenylyl cyclase

cAMP diffuses out of the cell into the medium

Internal cAMP inactivates the external receptor (to prevent it from following its own path)

A diff G PRO stimulates phospholipase C (producing IP3)

IP3 induces Ca2+ ion release

Ca2+ ions act on cytoskeleton to induce the extension of the pseudopodia

46
Q

what creates the oscillatory behavior in Dictyostelium movement?

A

internal cAMP concentration inactivates the receptor for external cAMP

cell fluctuates being able to detect & not detect cAMP

47
Q

what causes the Dictyostelium actin network to grow?

A

2nd messengers or redistribution of existing messengers

leads to local rearrangements of the cytoskeleton

48
Q

where does the inhibitory signal occur in Dictyostelium?

A

at all sites except the one stimulated with cAMP first

C Bio (30 decks)

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