Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Molecular Biology Exam II material > Lecture 19: Cytoskeleton > Flashcards

Lecture 19: Cytoskeleton Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

Functions of the cytoskeleton

A
  • Cytoskeleton represents bone of the cell
  • important in organization of the cell
  • Maintains correctly shaped cells
  • Ensures cells are properly structured internally
  • Change shape of the cell
    • RBCs and the erythrocyte membrane skeleton
      • RBCs must be flexible enough to get through tight capillary spaces
  • Moves the cell
  • Re-arranges the cellular compartment
  • Supports the Plasma membrane
  • Provide the mechanical strength
    • resistance to the stress without being ripped apart
  • Pulls chromosomes apart during cell division
  • Splits dividing cells during cell division
  • Guides intracellular traffic of organelles
  • Vesicles move around by using cytoskeleton as a sidewalk
  • cells like sperm need to swim-cytoskeleton acts as a motor
  • Muscle cell contraction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the 3 faimlies of cytoskeletal proteins

A
  • Actin filiaments
    • determine the shape of cell’s surface and are necessary for whole-cell locomotion, secretion, endocytosis
  • Microtubules
    • Form tube like structure
    • determine the positions of membrane enclosed organelles and direct the intracellular transport
    • make up centrioles and mitotic spindle
    • cilia and flagella
  • Intermediate filaments
    • provide mechanical strength
    • strong filament
      • resist mechanical stress
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Actin filaments

A
  • are two-stranded helical polymers of the protein actin
  • actin subunits are compact and globular (G-actin vs. F-actin)
  • Flexible structures 5-9 nm in diameter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Microtubules

A
  • Are long hollow cylinder
  • are made of tubulin subunits that are compact and globular
  • are long and straight
  • outer diameter 25nm
  • more rigid than actin filaments
  • have one end attached to a single microtuble-organizing center called a centrosome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Intermediate filaments

A
  • Are rope-like fiber, diameter 10nm
  • Large heterogeneous family
  • are made of smaller subunits that are themselves elongated and fibrous
  • extend across the cytoplasm to provide mechanical strength (iii)
  • span from one cell-cell junction to another to strengthen the epithelial sheet
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

___ allows fibroblast to crawl but also disassembles so cell can change shape to round prior to division. ____ forms a contractile ring at center of cell (with myosin) to split cells in division

A

Actin, actin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Microtubel cytoskelton consists of

A
  • long microbtubles that emanate from a single microtubule-organizing center
    • (note that the microtubles rearrange to form a bi-polar mitotic spindle)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

_____ maintains polarity for intestinal cells- apical surface vs. basolateral surface

A

The cytoskeleton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

____ are attached to desomosomes (adhesive structures) and to hemidesmosomes (cell matrix contact)

A

Intermediate filaments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

___ form tracks to get newly synthesized proteins to proper locations

A

Microtubules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Cytoskeletal filaments (or polymers) are held together by _______ interactions, which means that their assembly and disassembly can occur rapidly

A

weak noncovalent interactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

____ are long linear strings of protein subunits joined end to end

A

protofilaments

(note that protofilaments are thermally unstable- easy to break linear filament that is why you get multiple protofilaments bound side to side)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

assembly of actin or tubulin subunits (monomers) into linear polymer

A

Polymerization

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Removal of monomers at the ends of the polymer

A

Depolymerization

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

For new large filament to form, subunits must assmble into initial aggregate or nucleus. This initial process is called

A

nucleation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Formation of an actin nucleus is caused by

A

random collision of 3 subunits

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Course of formation of Cytoskeletal Filaments

A
  1. Filament nucleation-lag phase
    • a process of formation of initial aggregate, or nucleus
    • the rate limiting step
  2. Filament elongation-growth phase
    • Subunits are quickly added onto the ends of nucleated filaments
    • Eventually reach steady state in which the rate of monomer addition equals the rate of monomer loss
      • Which is the critical concentration called Cc
  3. Steady state-equilibrium phase
    • The rate of addition of new subunits balances the rate of dissociation subunits
    • the concentration of free subunits at this point is called critical concentration (Cc)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Tubulin is a hetero-dimer of

A
  • alpha-tubulin and beta-tubulin with non-covalent bonds
  • note that both have a binding site for one GTP btu the GTP in the alpha tubulin is never hydrolyzed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

1 microtubule is a hollow cylinder structure, consisting of

A
  • 13 protofilamnets aligned in parallel
    • longitudinal contact: alpha tubulin -beta tubulin
    • Lateral contact: alpha-tubulin - alpha tubulin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Actin monomer contains a binding site for

A

ATP or ADP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What creates structural polarity of microtubule

A
  • arrangement of alpha and beta tubulins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Actin Filament

A
  • Arranged head-to-tail to generate structural polarity
  • consists of 2 protofilaments, held by lateral contacts
  • are flexible and easily bent
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Plus end

A
  • Fast-growing or shrinking end
  • beta-tubulin or refered as barbed end of actin filament
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

minus end

A
  • Slow-growing or shrinking end
  • has alpha-tubulin or the GTP-binding clet on the actin monomer point toward minus end, also referred as pointed end
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Elongation proceeds spontaneously when

A

DeltaG for addition of the monomer is less than zerio, due to the [monomer] exceeds the critical concentration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Treadmilling predominates in ____ filaments

A

actin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is a Catastrophe in terms of Dynamic instability

A

if nucleotide hydrolysis proceeds more rapidly than subunit addition, the cap is lost and the microtubule begins ot shrink

28
Q

what is a rescue in terms of dynamic instability

A
  • GTP-containing subunits may still add to the shrinking end, and if enough add to form a cap, then microtubule grwoth resumes
29
Q

Dynamic instability predominates in

A

microtubules

30
Q

Construction of intermediate Filaments

A
  • Each monomer is an elongated molecule with an extended central alpha-helical domain (A)
  • Monomer forms a parallel coiled-coil dimer with another monomer (B)
  • A pair of dimers associates in an antiparallel manner to form a staggered Tetramer (C)
  • (note there is no nucleotide binding site and structural polarity)
  • Within each tetramer, the two dimers are offset, allowing it to associate with another tetramer (D)
  • Eight parallel tetramers (protofilaments) pack together laterally to form the filament (E)
31
Q

What is the most diverse group fo intermediate filaments

A

The Keratins

32
Q

Human genome: ___ distinct keratin genes. about ____ found in human epithelial cells

A
  • 50
  • 20
33
Q
A
34
Q

accessory proteins that conrol Assembly and position of cytoskeletal filaments: actin filaments

A
  • Actin subunits
    • Formin
      • nucleates assembly + remains associated with growing plus end (Remember: for new large actin filaments to form, subunits must assemble into initial aggregate or nucleus (nucleation))
    • Tymosin
      • Binds subunits, prevents assembly
    • Profilin
      • binds subunits, speeds elongation
    • ARP complex (actin related protein) nucleates assembly to form a web and remains associated with minus end
  • Actin Filaments
    • Cofilin
      • binds ADP-actin filaments, accelerates disassembly
    • Gelsolin
      • severs actin filaments and binds to plus end
    • Capping protein
      • prevents assembly and disassembly at plus end
    • Tropomyosin
      • stabilize filament
  • Filament bundling, cross linking and attachment to membranes
    • Fimbrin, alpha-actinin, filamin, spectrin (RBC cytoskeleton and HS), ERM family (Ezrin, Radixin, Moesin)
35
Q

Accessory Proteins that Control Assembly and Position of Cytoskeletal Filaments: Microtubules

A
  • Tubulin dimers
    • Staminin
      • binds subunits, prevents assembly
    • gamma-TuRC
      • (gamma-tubulin ring complex) nucleates assembly and remains associated with minus end
    • TIPS
      • (plus end tracking proteins) remain associated with growing plus ends, and can link them to toher structures (e.g. membrane)
  • Microtubules
    • Kinesin 13:
      • enhances catastrophic disassembly at plus end
    • Katanin:
      • (Japanese work for “sword” severs microtubules
    • MAPS: (Microtubule associated protein)
      • stabilizes tubules by binding along sides
    • XMAP215
      • A microtubule associated protein that stabilizes plus ends and accelerates assembly
  • Filament cross linking
    • Tau (a MAP protein), MAP2:
      • both cause bundling of microtubules
    • Plectin
      • cross-linking protein
      • links microtubules to intermediate filaments
36
Q

Microtubules are nucleated from a specific location, called

A

microtubule-organizing center (MTOC)

37
Q

_____ is responsible for the nucleation of microtubule growth

A

gamma-tubulin ring complex (gamma-TuRC)

38
Q

a centrosome consists of a fibrous centrosome matrix to which the gamma-TuRCs are attached- greater than ___ copies of gamma TuRCs

A

50

39
Q

embedded in the centrosome is a pair of cylindrical structures, called _____, arranged at right angle to each other

A

centrioles

40
Q

Microtubules are nucleated at the centrosome at their _____ end, with ____ pointing outward and grow toard the cell periphery

A

minus end, plus end

41
Q

nucleation of actin filaments occurs at or near the

A

plasma membrane, thus actin filaments mostly accumulate at cell periphery

42
Q

Lamellipodia

A

flat protrusive veils of actin

43
Q

Filopodia or microvilli

A

spiky bundles of actin

44
Q

actin polymerization is regulated by

A

ARP complex and Formins

45
Q

Actin-Related Protein or ARP (Arp 2/3) Complex

A
  • Two ARP proteins, Arp2 and Arp3, are 45% identical to actin
  • Function similar to gamma-TuRC, the ARP complex nucleates actin filament growth from the minus end, allowing elongation at the plus end
  • Require activating factor
  • in abscence of activating factor, Arp2 and Arp3 are masked by their accessory proteins to prevent them from nucleating a new actin filament
  • Binding to the activating factor induces conformation change that resembles the plus end of actin filament, allowing actin monomers to bind, bypassing the rate-limiting step of filament nucleation
46
Q

what is ActA

A
  • it is a surface protein of Listeria
  • It activates Arp 2/3 complex causes local nucleation of actin filaments which are cross linked
  • Growing filaments are the driving force to push cell through cytoplasm
47
Q

ARP comlex works most efficiently when it is

A
  • bound to the side of preexisting actin filament-filaments cross linked
    • filament branch grows at 70 degress angle relative to the original filament
48
Q

_____ nucleate the growth of straight and un-branched actin filaments

A

Formins

49
Q

Formins

A
  • Nucleate the growth of straight and un-branched actin filaments
  • A large family of dimeric proteins, with each formin subunit having a binding site for an actin monomer
  • Formin dimers nucleate actin filament polymerization by capturing two monomers at the plus end or the growing end of an actin filament
  • Formin proteins form a dimeric complex that can nucleate the formation of a new actin filament and remain associated with the rapidly growing plus end as it elongates
  • different from gamma-TuRCs, nucleating tubulin polymers, because they bind to minus end of filament
50
Q

How is there a large pool of actin polymers always kept available with all the nucleation of actin filaments occurring in the cell

A
  • Tymosin
    • keeps actin monomers soluble so they are readily available for generating filaments
      • Actin monomers bound to thymosin are in locked state, where they cannot associate with actin filaments, this causes high concentration of soluble actin monomers in cells
51
Q

______ recruits actin monomers to the actin filament for polymerization

A
  • Profilin
    • Profilin binds to the actin monomer to expose the site of actin that binds to the plus end of the actin filament
    • The addition of an actin monomer to the filament induces conformation change in the actin that reduces its affinity for profilin
    • so the profilin falls off, leaving actin filament one subunit longer
    • profilin competes with thymosin in binding to individual actin monomers
52
Q

Proteins that regulate the availability of actin monomers for actin polymerization

A
  • Thymosin
  • Profilin
53
Q

_______ are proteins that bind along the sides of microtubules, that alter the filament’s stability and mechanical properties

A
  • Microtubule-associated proteins (MAPs)
    • stabilize microtubules against disassembly, contain at least two domains, one domain for binding to microtubule and another that project outward
54
Q

MAP2 vs. Tau

A
  • MAP2 has a long projecting domain with a second microtubule-binding domain at the other end, thus forming bundles of stable microtubules that are kept widely spaced
  • Tau binds to the microtubule at both its N- and C-termini, with a short projecting loop, forming bundles of more closely packed microtubules
55
Q

Regulation of Stability proteins of Actin Filament

A
  • Tropomyosin
    • Actin filaments are stabilized by the binding of tropomyosin (an elongated protein)
    • binding of tropomyosin prevents the actin filament interacting with other proteins (tropomyosin is a key protein in erythrocyte membrane skeleton)
  • Cofilin
    • actin depolymerizing factor
    • binds to both actin filament and free actin subunits
    • binding of cofilin forces the flament to twist a little more tightly, weakens the contacts between actin subunits, making the filament brittle and more easily severed
    • Cofilin prefers to bind to ADP-containing actin filaments, thereby efficiently disassembling the older filaments
    • Actin filaments can be protected from cofilin by tropomyosin
56
Q

Kinesin-13 proein family

A
  • Catastrophe factor
  • increase the rate at which a microtubule switches from a growing to a shrinking state
  • They bind to microtubule ends and pry protofilaments apart by lowering the activation energy barrier that prevents a microtubule from sprining apart into the curved protofilament
57
Q

Actin filaments are organized into

A

two types of arrays, Bundle (Formin makes bundles) and web-like(gel-like) network (formed by ARP complex)

58
Q

Actin filament cross-linking proteins help to stabilize and maintain these structures and are divided into 2 classes:

A
  • Bundling protein
    • cross-links actin filaments into a parallel array
    • alpha-actinin, fimbrin, and villin
  • gel-forming protein
    • holds two actin filaments together at a large angle to each other to create a looser meshwork
59
Q

Alpha-actinin vs. fimbrin

A
  • alpha actinin
    • cross-links actin filaments into loose bundles, allowing myosin II to enter to make actin filaments contractile
  • Fimbrin
    • cross-links actin filaments into tight bundles, excluding myosin II
  • They tend to exclude on another because of different functions
60
Q

villin is associated with

A

microvilli

61
Q

_____ connect the sides of actin filament bundle to the plasma membrane in microvilli

A

Lateral sidearms (myosin-I, calmodulin)

62
Q

filamin promotes theformation of losse and highly viscous gel-like network by clamping together

A

2 actin filaments roughly at right angles

63
Q

cells require the actin gel formed by filamin in order to

A
  • extend membrane projections which help cells ot crawl across a solid surface
    • cells without filamin cannot crawl properly, and they produce disorganized membrane blebs
64
Q

Cell migration can be conceptualized as a cyclic process, involving three distinctive activities

A
  • Polarization and Protrusion
    • The molecular processes at the front and the back of a moving cell are different. Actin-rich structures are pushed out at the front of the cell
  • Adhesion (Attachment) and Traction:
    • adhere to extracellular matrix (ECM) or adjacent cells via transmembrane receptors linked to the actin cytoskeleton. Adhesions serve as traction sites for migration as the cell moves forward over them.
  • Re-traction
    • adhesions are disassembled at the cell rear, allowing the bulk of the trailing cytoplasm to be drawn forward
65
Q

Different types of protrusive structures, all have a dense core of actin filaments and no membrane-enclosed organelles

A
  • Filopodia (microspikes)
    • formed by migrating fibroblasts
    • one-dimensional
    • contain a core of long, bundled actin filaments
  • Lamellipodia
    • formed by epithelial cells, fibroblasts and neurons
    • two-dimensional, sheet-like structure
    • contains cross-linked mesh of actin filaments, most lie in a plane parallel to the solid substratum
  • Pseudopodia
    • Formed by amoebae and neutrophils
    • Three-dimensional projections filled with an actin-filament gel

Molecular Biology Exam II material (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions