Brainscape's Knowledge GenomeTM

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


See full index

Hilary Term 1 > Cytoskeleton II – Actin Network > Flashcards

Cytoskeleton II – Actin Network Flashcards

1
Q

Describe the cytoskeleton

A
  • dynamic intracellular network
  • drives movement of intracellular organelles and whole cells
  • involved in muscle contraction
  • organises and provides structural support for the cell
  • controls cell shape
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Describe actin

A
  • microfilaments
  • 7nm
  • found in all eukaryotes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe tubulin

A
  • microtubules
  • 25nm
  • found in all eukaryotes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe intermediate filaments

A
  • 10nm
  • vimentin, cytokeratin, desmin
  • found only in animals
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe the filaments

A

long unbranched one-dimensional protein polymers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe actin microfilaments

A
  • linear polymers of G-actin
  • F-actin microfilaments are helical polymers
  • left-handed helix with a rotation of 166 degrees per subunit
  • 13 monomers per helix repeat of 37 nm
  • 7 nm diameter
  • flexible ‘ropes’
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

G-actin

A
  • a single globular protein
  • monomeric G-Actin
  • binds one ATP
  • hydrolyses ATP
  • subdomain 2-4 surface binds to subdomain 1-3 surface, resulting in filament polarity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

F-actin

A

filamentous actin

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

Describe actin filament dynamics

A
  • “in vitro treadmilling”
    • end has the highest binding affinity to G-actin
  • post-polymerisation into microfilaments, actin monomers hydrolyse their bound ATP; destabilises the filament
  • ADP-binding subunit dissociation from - end
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens in F actin at the - end

A
  • releases G-actin ADP and Pi
  • G-actin releases ADP
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens in F actin at the + end

A

ATP binds to G-actin, which binds to F-actin

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

Describe treadmilling

A

actin filament elongates at + end and shrinks at - end

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

Describe actin dynamics in vivo

A
  • controlled by actin binding proteins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

List the functions of actin binding proteins

A
  • nucleation
  • capping
  • severing
  • sequestering
  • bundling
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Actin binding proteins determine

A

rate of filament assembly and stability

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

Describe the functions of the microfilaments

A
  • strong in tension, weak in compression (better for pulling than pushing)
  • linear pathways for organelle movement in plants and fungi
  • in animals, form contractile systems together with motor-proteins
  • when cross-linked, have a variety of structural roles; can push the growing margins of an animal cell forward
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe myosin motor proteins

A
  • protein family
  • two catalytic ATPase heads walk along actin filament
  • motor heads convert chemical energy released by the hydrolysis of ATP into mechanical movement
  • motor domain is connected via a neck domain to a tail domain, which interacts with cargo or dimerises
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe Myosin-II

A
  • 2nm
  • C terminus connects to coiled-coil of two light chain alpha-helices
  • neck or hinge region connects N terminus
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Describe organelle and vesicle transport in plants

A
  • small organelles and vesicles are continuously moved around the cytoplasm
  • drag caused by moving organelles causes cytoplasmic streaming
  • movement is powered by actin filaments, using myosin motor proteins
  • used to overcome diffusion barriers in extremely large vacuolate plant cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

cytoplasmic streaming

A

the whole cytoplasm cycles round the cell

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

Describe actin and myosin-II in animals

A

form contractile arrays

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Describe the skeletal muscle - the basics

A

a contractile machine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Describe muscle fibres in animals

A
  • giant multinucleate syncitial cells
  • 50 μm in diameter
  • formed by the fusion of myoblasts
  • within each fibre are many myofibrils, forming the contractile apparatus
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

myoblasts

A

mononucleated precursors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Describe muscle fibre formation

A

myoblasts make myotubes form myofibrils

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

Describe sarcomeres

A
  • each myofibril is a highly organised linear array of sarcomeres
  • actin-containing thin filaments project with opposite polarities from the two Z-discs
  • interdigitating between the thin filaments are thick filaments
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Sarcomeres

A

contractile units

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Z-discs

A

embed the actin plus-ends

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What are the sarcomere filaments composed of?

A

myosin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Describe myosin thick filaments

A
  • spontaneously assembles
  • bipolar with a bare central zone
  • myosin heads project out sideways in nine radial positions
  • three-fold symmetry
  • period of 43 nm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Describe nebulin

A
  • giant protein
  • acts as a molecular ruler that controls the lengths of the thick and thin filaments
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Describe titin

A
  • giant protein
  • acts as a molecular ruler that controls the lengths of the thick and thin filaments
  • elastic ends hold thick filaments in the centre of the sarcomere
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Describe thick and thin filament attachment

A
  • plus end: Z disc and Cap Z
  • titin and nebulin
  • tropomodulin at - end
  • M line
  • myosin thick filament
  • actin thin filament
  • ends with other Z disc
34
Q

Describe the sliding filament model of contraction

A
  • sliding of the two filament sets, without change in filament lengths creates shortening of the sarcomere
  • myosin molecules binding to actin filaments and pulling them towards the centre of the sarcomere
  • actin is in tension
35
Q

Describe the myosin cross-bridge cycle

A
  • myosin head undergoes dramatic changes in conformation depending on its binding
  • power stroke
  • distance moved by each myosin head is ~6 nm
    force generated is 0.7x10-12 N (0.7 piconewtons)
  • heads are detached most of the time (~95% of the duty cycle)
36
Q

Describe the ‘power stroke’

A

Pi release causes strong filament binding and conformational change in neck region

37
Q

Describe a cross section of insect flight muscle

A

thick filaments are hexagonally packed with great regularity

38
Q

Describe myosin cross-bridge binding

A
  • spacing of myosin heads is out of register with spacing of the myosin binding sites on the actin thin filament
  • symmetry of myosin heads and surrounding actin binding sites differ
  • myosin heads cannot all bind actin at the same time
  • ensure some heads are attached at all times to maintain tension
39
Q

Describe myosin head and binding site spatial discrepancy

A

– myosin heads repeat distance: 129 nm
– each head moves ca. 6 nm per cycle
– repeat distance of the myosin binding sites on the actin filaments: 37 nm

40
Q

Describe the asymmetry of myosin heads and actin binding sites

A

– myosin heads stick out in nine radial positions
– each thick filament it is surrounded by six actin filaments

41
Q

Describe the co-ordination of actin-myosin interactions

A
  • thin filament contains accessory proteins troponin and tropomyosin
  • two calcium ions bind to troponin C
  • troponin complex changes shape, induces tropomyosin to roll away from the myosin binding site on the actin microfilament
  • myosin can bind to the actin filament and cause contraction
  • contraction continues as long as calcium ions are present
42
Q

Describe how calcium release co-ordinates contraction

A
  • released from stores in the SR
  • resting calcium levels in the sarcoplasm are ~10-7 molar
  • within the SR, calcium concentration is about ~10-3 molar (10,000 times greater)
  • SR membrane is in electrical contact with the plasmamembrane
  • arrival of an action potential opens calcium channels in the SR, increasing Ca2+ about 10-fold
43
Q

SR

A
  • specialised endoplasmic reticulum of the muscle fibre
  • sarcoplasmic reticulum
44
Q

the sarcoplasm

A

the muscle cytoplasm

45
Q

Describe a muscle cell

A
  • plasma membrane
  • myofibrils
  • transverse tubules form invaginations of plasmamembrane
  • SR
46
Q

Describe cytokinesis in animals and fungi

A
  • cytokinesis after mitosis is brought about by a contractile ring of actin and myosin II
  • form a ring of mini sarcomere-like structures
47
Q

What is the contractile ring composed of?

A

actin and myosin filaments

48
Q

Describe the distribution of actin and myosin II during cytokinesis in normal Dictyostelium discoideum cells

A
  • actin: spread across cell
  • myosin II: centralised
49
Q

Describe microfilament organization in non-muscle cells

A
  • cytoplasmic bundles of F-actin and myosin-II form stress fibres
50
Q

Describe stress fibres - the basics

A
  • focal adhesion point
  • peri-nuclear cage or PM
  • stress fibres are contractile actin arrays
  • can be visualised in fibroblast cells with red actin and blue nucleus staining or with deep etching and rotary shadowing
51
Q

Describe the focal adhesion point of stress fibres

A

anchored to other cells or extracellular matrix by the PM

52
Q

Describe the structure of stress fibres

A
  • contain both bipolar actin filaments and myosin II mini- filaments
  • contractile
  • mini-sarcomeres
53
Q

Describe actin polymerisation

A
  • can drive rapid cell migration
  • e.g. keratocytes from fish scales (~15 μm per minute)
54
Q

Describe microfilament organisation in crawling cells

A

Lamellipodium

55
Q

Describe stress fibres in crawling cells

A
  • contractile bundles
  • push the trailing edge
56
Q

Filopodium in crawling cells

A
  • small, dynamic cell
    projections
  • actin bundle
  • senses environmental
    signals
57
Q

Lamellipodium in crawling cells

A
  • large, flattened cell
  • extension at the leading edge
  • quasi-2D branched actin
    meshwork
  • pulls the cell forward
58
Q

Describe the crawling cells

A
  • filopodium and microspike
  • lamellipodium
  • adhesion sites
  • lamella
  • arcs
  • stress fibres
59
Q

Describe the leading edge of a crawling cell

A
  • lamellipodia contain dense network array of short branched actin filaments
  • provide enough rigidity to push on the membrane at the leading edge
  • 70 degree intersections
60
Q

Describe ARPs

A
  • organise branched arrays
  • ARP2/3 complex can bind to pre-existing actin filaments at a 70 degree angle
  • nucleate formation of new filaments creates a cross-linked meshwork
  • analogous to g-Tubulin nucleating MT
61
Q

ARPs

A

actin-related proteins

62
Q

Describe the array treadmilling model for lamellipodium extension

A
  • individual actin filaments become capped at both ends, then remain constant in length, and stationary with respect to the array (and to the substrate over which the cell moves)
  • the array as a whole grows forward, polymerising at the front and depolymerising at the rear
  • array can thus be described as treadmilling, although the individual filaments are not
63
Q

What happens at the leading edge of crawling cells?

A

net filament assembly

64
Q

What happens behind the leading edge of crawling cells?

A

net filament disassembly

65
Q

How is lamellipodium protrusion (new extension growth) at the leading edge mediated

A
  • actin polymerisation without the involvement of myosin II
66
Q

What do the focal contacts of crawling cells contain?

A

integrins

67
Q

Describe the spatial organisation of actin polymerisation

A

G-proteins

68
Q

G-proteins

A

Small, GTP-binding GTPases

69
Q

Describe some G-proteins

A
  • Rho stimulates stress fibre production
  • Rac stimulates extension of lamellipodia
  • Cdc-42 stimulates formation of filopodia
  • can be viewed under staining
70
Q

Describe G-proteins and cell control

A
  • G-proteins can bind either GTP or GDP
  • slowly cleave GTP to GDP
  • when GTP is bound, G-proteins are in an activated state and
    can stimulate other proteins
  • act as molecular switches and control cellular activity
  • switching controlled by other factors
71
Q

switching

A

GTP binding and release

72
Q

How are crawling cells activated?

A

GTP acquisition (fast!)

73
Q

How are crawling cells inactivated?

A

GTP hydrolysis into GDP, which is released (slow!)

74
Q

Describe the interaction among cytoskeletal elements - the basics

A
  • necessary for most cellular processes (e.g. cell division and cell migration)
  • requires coordination among cytoskeleton components
75
Q

Describe some specific interactions among cytoskeletal elements

A
  • static crosslinkers
  • motor proteins
  • motor protein-binding protein complices
76
Q

Actin polymerisation is based on …

A

binding and hydrolysis of ATP

77
Q

When cross-linked or linked to the substratum actin can…

A

act under compression to force forward cell membranes in motile cells

78
Q

Actin can act under tension in contractile systems in single cells and tissues

A
79
Q

spatiotemporal control of actin polymerisation is controlled by

A

small GTPases, that are themselves controlled by diverse spatiotemporal signals from the cell’s internal activities and environment

80
Q

Actin based cytosplasmic streaming is used to overcome

A

diffusion barriers in extremely large plant cells

81
Q

Interaction among cytoskeleton elements ensures

A

coordinated cellular function

Hilary Term 1 (61 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions