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Biology 360 > Topic 6 - Cytoskeleton > Flashcards

Topic 6 - Cytoskeleton Flashcards

1
Q

What are the three types of cytoskeletal filaments?

A
  1. Intermediate filaments
  2. Microtubules
  3. Actin filaments
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2
Q

What is the purpose of the intermediate filaments?

A

Provide strength for the cell

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3
Q

What is the function of microtubules in the cell? (2)

A

Determine the positioning of organelles

Associate with motor proteins

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4
Q

What are the functions of actin filaments in the cell? (2)

A

Determine the shape of the cell surface

Responsible for whole cell locomotion

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5
Q

Cytoskeletal filaments would not be able to function without (broad term)

A

Accessory proteins

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6
Q

Intermediate filaments are only present in… (phyla, 3)

A

Vertebrates, nematodes, mollusks

In other words, “squishy” animals

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7
Q

Microtubules and actin filaments are only present in (taxonomic group)

A

Eukaryotes

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8
Q

Rank the general size in width of microtubules, intermediate filaments, and actin filaments from largest to smallest

A

Microtubules > Intermediate > Actin

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9
Q

Describe what cytoskeletal elements are important in mitosis and cytokinesis

A

Microtubules: form the mitotic spindle
Actin: forms a contractile ring to cleave cell during cytokinesis

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10
Q

When a cell is in motion (like a neutrophil chasing a bacterium), what part of the cytoskeleton is responsible for leading the movement of the cell?

A

Actin filaments

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11
Q

What element of a cell is responsible for a cell’s polarity?

A

The cytoskeleton (actin and microtubules, intermediate filaments are nonpolar)

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12
Q

Intermediate filaments adhere to (2) on the periphery of the cell

A

Desmosomes and hemidesmosomes

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13
Q

In non-polar cells, microtubules are arranged like…

A

Stars

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14
Q

In polar cells, microtubules are often arranged in this way…

A

Linear - helps create cell polarity

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15
Q

In polar cells (like epithelial cells), actin-dense areas on neighbouring cells are attached to each other via…

A

Adherens junctions

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16
Q

Why does the cell disassemble filaments and reassemble them as opposed to moving assembled filaments?

A

It is much harder to move an entire filament, but individual monomers can diffuse easily through the cell to produce continuous movement

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17
Q

Describe the + end of an actin or tubulin polymer

A

The fast-growing end

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18
Q

Describe the - end of an actin or tubulin polymer

A

The slow-growing end

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19
Q

What happens to a monomer of actin or tubulin when it goes from being free to being a part of a polymer?

A

It undergoes a conformational change

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20
Q

What are the 2 forms of actin and tubulin monomers?

A

T-form and D-form

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21
Q

When actin is in its T-form, it is bound to…

A

ATP

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22
Q

When tubulin is in its T-form, it is bound to…

A

GTP

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23
Q

When actin is in its D-form, it is bound to…

A

ADP

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24
Q

When tubulin is in its D-form, it is bound to…

A

GDP

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25
An ATP/GTP cap is formed when...
Addition of subunits is faster than ATP or GTP hydrolysis
26
Monomers of actin and tubulin are added in the (1) form
T-form
27
Monomers of actin and tubulin dissociate from the polymer in the (1) form
D-form
28
Define the critical concentration of actin and tubulin monomers
The concentration at which the rate of polymerization is equal to the rate of depolymerization (addition = subtraction)
29
Define persistence length
Measures the stiffness of a filament: The minimum length of a filament at which random thermal fluctuations are likely to result in bending of the monomer
30
A small persistence length means...
The substance is flexible, even short lengths will bend in an energetically favourable way
31
What is the persistence length of actin?
20-40 um
32
In situations where actin is kept from bending, what is required to do this?
Accessory proteins
33
Which end of an actin monomer (+ or -) binds ATP?
- end
34
Describe what is happening to actin polymers during treadmilling
Net addition on one end of the polymer and net loss at the other end
35
What is profilin?
A protein which associates with actin to PROMOTE POLYMERIZATION
36
What is thymosin?
A protein which associates with actin monomers to INHIBIT POLYMERIZATION
37
Is it true that actin monomers can bind both profilin and thymosin?
No, can only bind one at a time
38
What is "nucleation"?
The initial process of actin polymerization in which 3 actin monomers come together to form the beginning of an actin filament
39
Actin filament nucleation occurs most commonly at or near...
The plasma membrane
40
Actin filament nucleation is regulated by...
External signals, i.e. cell signalling pathways
41
Actin filament nucleation is specifically regulated by (2)
ARP complex or formins
42
When active, ARP complexes...
Enhance polymerization of actin
43
Which end (+ or -) of the actin monomer does ARP bind to?
- end
44
When ARP binds to the - end of an actin filament, (1) is prevented
Depolymerization
45
when ARP binds to existing actin filaments, what happens?
Typically creates a branch 70 degrees off from the original branch - creates a meshlike 2D network of actin
46
Formins produce (branched/unbranched) actin filaments
Unbranched
47
Describe the "anatomy" of a formin
2 subunits (a dimer), each hold 1 actin monomer
48
Formins associate with the (+/-) end of an actin filament
+ end
49
How can the rate of polymerization or depolymerization of cytoskeletal filaments be altered?
With the addition of capping proteins
50
The two general forms of actin arrays in a cell are...
Bundles and networks
51
Actin bundles are made of (branched/unbranched) filaments
Unbranched
52
Actin networks are made of (branched/unbranched) filaments
Branched
53
How are actin bundles spaced out?
With the addition of alpha-actinin between the actin fibers to space them out
54
The presence of alpha-actinin in cytoskeletal arrangements allows this to come between actin fibres
Myosin-II
55
To prevent myosin-II from entering between contractile bundles, what protein holds actin filaments close to each other?
Fimbrin
56
Fimbrin is a (-imer)
Monomer
57
Alpha-actinin is a (-imer)
Dimer
58
A bundle of actin fibers will have this mixture of accessory proteins to properly space the fibers together
Trick question: there will only be either alpha-actinin or fimbrin, not both in a given bundle
59
What is filamin?
An accessory protein which associates with actin filaments to hold networks of actin filaments together
60
Filamin is a (-imer)
Dimer
61
Myosin is found in all members of this taxonomic grouping
All eukaryotes
62
In humans, how many distinct myosin families are there?
37
63
All (except 1) myosin type walk towards the (+/-) end of an actin filament
+ end
64
In order to produce "walking" movement, myosin uses...
ATP hydrolysis
65
Describe the anatomy of a myosin molecule
2 heavy chains (with globular heads, site of ATP hydrolysis) 2 light chains (associate with the head region) The a-helix "tails" of myosin associate with other myosin dimers and form a bundle
66
What does it mean for a myosin bundle to be "bipolar"?
Myosin heads are oriented in opposite directions on either side of the "bare zone"
67
What causes rigor mortis?
In the absence of ATP upon death, the body tenses up due to the tight bond between actin and myosin
68
What stops rigor mortis?
Decomposition/breakdown
69
In the actin-myosin binding cycle, how often (in %) is myosin bound to actin?
Only 5% of the time, need to be able to synchronize this movement
70
How long (in nanometers) is each "step" of myosin-II?
8.5 nm
71
The power stroke of the actin-myosin binding cycle is caused by...
The removal of ADP from the N-terminal head group of myosin
72
What are the 3 sites of the troponin complex?
``` I = Inhibitory C = calcium binding T = tropomyosin binding ```
73
When there is no Ca++ present, is tropomyosin in or out of its groove?
Out of its groove - preventing the interaction of actin and myosin
74
When Ca++ is PRESENT, is tropomyosin in or out of its groove?
In its groove - out of the way, allows interaction of actin and myosin
75
Where are troponin complexes located in comparison to tropomyosin?
Troponin complexes at the end of tropomyosin molecules
76
How many Ca++ ions bind to the troponin complex?
4
77
What form of myosin carries cargo (like vesicles and organelles) along actin filaments?
Myosin V
78
Are there myosins in plants?
Yes! In all eukaryotes
79
The lever arm swing in Myosin V is this many nanometers long
30-40 nm
80
What are the 2 major groups of proteins that interact with actin filaments?
1. Motor proteins | 2. Accessory proteins
81
Tubulin is a (-imer)
Heterodimer: contains alpha and beta subunits
82
GTP can only be exchanged from (alpha/beta) subunits of microtubules
Beta
83
One strand of a mictotubule is called a...
Protofilament
84
The only exception where an alpha is not next to an alpha in a microtubule is...
At the "microtubule seam"
85
How many protofilaments are in a microtubule?
13
86
What protein is required for nucleation of microtubules?
gamma-tubulin
87
Nucleation of a microtubule starts at...
The microtubule-organizing center (MTOC) also known as the centrosome
88
What acts as the "template" which creates microtubules?
The gamma-tubulin ring complex
89
What makes up the gamma-tubulin ring complex?
7 gamma tubulins (each with 2 heads) and accessory proteins
90
What is a centriole?
A short cylinder of modified microtubules and accessory proteins
91
Microtubule complexes are very stable when arranged in a (1) configuration
Star/astral
92
In a case where microtubules are linear to make a polar cell, centrosomes will be...
At one end of the cell
93
Describe the MTOCs of plants and fungi
Have centrosomes (the complex that microtubules stem from) but do not have centrioles
94
If a cell is fragmented and microtubules are cut off from the MTOC, what will happen?
Microtubules will reform a MTOC, but it will not have any centrioles
95
Kinesin-13 and XMAP215 are examples of...
Microtubule binding-proteins, or MAPs
96
What end of a microtubule (+ or -) do dyneins move towards?
The - end
97
What are the largest and fastest motor proteins? (excluding the special myosin)
Dyenins: move at 14 um/s
98
What energy source do motor proteins use?
ATP (do NOT use GTP)
99
The "motor" of motor proteins is contained within...
The head region
100
When in dimer form, intermediate filaments are (polar/nonpolar)
Polar
101
When in tetramer form, intermediate filaments are (polar/nonpolar)
Nonpolar
102
How many tetramers associate to form a intermediate filament unit?
8 tetramers, can be joined to other groups end-to-end
103
What is the persistence length of intermediate filaments?
less than 1 um - very bendy!
104
Intermediate filaments are stabilized by...
Strong lateral hydrophobic interactions
105
Keratin, desmin, and neurofilaments are all kinds of...
Intermediate filaments
106
Keratin is found in this cell type
Epithelial cells
107
Neurofilaments are found in this cell type
Axons
108
Desmin is expressed in...
Muscle, all three types of it!
109
Do bacterial cells have a cytoskeleton?
Yes - they just don't have exact same cytoskeletal elements, no intermediate filaments and have homologs for actin and myosin
110
What is special about fly embryonic development
Many nuclei form and then cellularization occurs
111
Tissue with many nuclei (like the fly embryo before cellularization) is called...
Synctium
112
Does the S phase take longer in humans or prokaryotes?
Longer in humans
113
What is the difference between mitosis and cytokinesis?
``` Mitosis = 2 nuclei Cytokinesis = 2 cells ```

Biology 360 (12 decks)

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