Chapter 4: 4.1 Cytoskeletal Proteins Flashcards
1
Q
What is the cytoskeleton?
A
A network of protein filaments that extends throughout the cytoplasm
2
Q
Cystoskeletal filaments are…
(2 points)
A
- Dynamic
- Can re-organize
3
Q
Cytoskeletal filaments are dynamic and can re-organize, what does this allow?
A
Allows cells to:
* Change shape
* Interact with the enivronment
* Move
* Organize cellular compartments
4
Q
How many types of protein filaments are in the cytoskeleton? List them out
A
3
1. Intermediate Filaments
2. Microtubules
3. Actin Microfilaments
5
Q
Describe:
Intermediate filaments
A
Rope-like filaments composed of a family of keratin proteins
6
Q
Describe:
Microtubules
A
Hollow cylinders made of tubulin dimers
7
Q
Describe:
Actin microfilaments
A
Helical polymers of actin protein
8
Q
List the functions of:
Intermediate filaments
A
- Provide mechanical strength
9
Q
List the functions of:
Microtubules
A
- Involved in organization of organelles and vesicles
- Form the mitotic spindle
- Major component of flagella and cilia
10
Q
List the functions of:
Actin microfilaments
A
- Involved in cellular movement
- Involved in skeletal muscle contraction
- In plants, involved in organization of organelles and vesicles
11
Q
Provide:
The etymology for Intermediate filaments
A
Named for their intermediate size, relative to actin and microtubules
12
Q
True or False:
Flagella and cilia are not the only type of cytoskeletal structure in prokaryotic cells namely bacteria
A
False, they are
13
Q
What do intermediate filaments enable cells to do? How?
A
Enables cells to withstand mechanical stress, by distributing the effects of locally applied force
14
Q
What do intermediate filaments consist of?
A
Long, twisted strands of fibrous proteins
* ~10 nm in diameter
* Composed of various helical protein types (e.g. keratin)
15
Q
True or False:
Intermediate filaments are not dynamic
A
True, they are not as dynamic as microtubules and actin filaments
16
Q
Where are intermediate filaments located in the body?
A
Have rolls in:
* Cell junctions
* Muscle contraction
* Neurons
* Nuclear structure
17
Q
True or False:
Intermediate filaments usually work with microtubules and actin filaments to carry out their functions
A
True
18
Q
Describe:
Monomer Intermediate Filaments
A
- Has a central rod-shaped domain (elongated α-helix)
- Has unstructured terminal domains (not globular like microtubules and microfilaments)
19
Q
True or False:
Central domains of different intermediate filament types are different in size and primary structure
A
False, they are similar in size and primary structure
20
Q
What are exposed on the surface of intermediate filaments? Why?
A
Terminal domains, allos interactions with cytoplasmic components
21
Q
Describe:
Dimer Intermediate Filaments
A
Coiled coil; two monomers intertwined
22
Q
Describe:
Tetramer Intermediate Filaments
A
Two dimers, running in opposite directions
* Dimers do not overlap completely, but are instead staggered
23
Q
True or False:
The two ends of tetramers are the same
A
True
24
Q
Are intermediate filaments non-polar? Microtubules? Actin microfilaments?
A
Intermediate filaments are non-polar
* Microtubules and actin microfilaments are polar
25
How do tetramer intermediate filaments assemble?
Assemble into a rope-like intermediate filament
* Interacts at the ends of each tetramer and at the sides
26
The extracellular matric can also maintain a connect between cells with the help of...
Cytoskeletal proteins
27
# Define:
Desmosomes
Connections made by intermediate filaments, keep cells tightly bound (e.g. skin cells)
28
# Define:
Gap junctions
Channels that form between cells to allow molecules to be shared between cells
29
# Define:
Tight junctions
Held together by cell adhesion molecules called CAMs
30
What are examples of CAMs?
* Cadherin
* Integrins
* Selectins
31
What are microtubules crucial for?
The interior organization of cells
32
# Explain:
Role of microtubules during interphase
Associate with motor proteins that transport or position organelles and vesicles
33
# Explain:
Role of microtubules during cell division
Form the mitotic spindle
* Ensures that chromosomes are correctly divided between the two daughter cells
34
Microtubules form the core of...
Flagella and Cilia
35
# True or False:
Microtubules are dynamic
True
36
What does it mean that microtubules are "dynamic"?
They are able to rapidly disassemble and reassemble
37
# Define:
Dynamic instability
The ability to switch between phases of assembly and disassembly
38
How many categories of microtubules are there? What are they?
2 main categories:
1. Cytoplasmic
2. Axonemal
39
# Describe:
Cytoplasmic microtubules
* More dynamic
* Located throughout cytosol
40
# Describe:
Axonemal microtubules
* Less dynamic and more stable
* Located in cilia and flagella
41
Microtubules originate/grow outward from...
Microtubule Organizing Centres (MTOCs)
42
# Define:
Centrosomes
A type of MTOC found in animal cells
* Consist of a pair of centrioles surrounded by various proteins, including the γ-tubulin ring complex
43
# Define:
Protofilament
A single chain of tubulin dimers, alternating between α- and β-tubulin
44
# Describe:
Microtubule structure (in terms of protofilaments)
13 protofilaments bind laterally to form a hollow, tube-like structure
45
# Describe:
Microtubule size in comparison to other fibers
* Larger (~10-25 nm) than actin microfilaments
* Larger than intermediate filaments
46
# State:
The Function of Microtubules
| (4 points)
* Structural support
* Organization of cytoplasm - positioning of organelles
* Transport ("roads" for motor proteins)
* Segregation of chromosomes during cell division (mitotic spindle)
47
Microtubules are dynamic. What does that mean?
They are abel to rapidly diassemble and reassemble
48
The microtubules' ability to switch between phases of assembly and disassembly is called...
Dynamic Instability
49
# Describe:
Tubulin
A heterodimer of α-tubulin and β-tubulin
50
What does β-tubulin bind to?
GTP
* Over time is hydrolyzed to GDP (has GTPase activity)
51
# Describe:
GTP-tubulin dimers
Have straight conformation
* Can more easily assemble
52
# Describe:
GDP-tubulin dimers
Have a curved conformation
* Are prone to disassemble
53
# In microtubules:
When is assembly promoted?
If most of the plus-end tubulin dimers are GTP-bound
* Creates a **GTP cap**, with a straight conformation
54
What does the loss of a GTP cap mean?
Curved dimers are exposed at the plus end
* Causes rapid disassembly
55
In vitro, microtubules can assemble and disassemble...
Spontaneously
56
In vitro, microtubules can assemble and disassemble spontaneously. What is this driven by?
Driven by the concentration of tubulin dimers and by whether GTP or GDP is bound to β-tubulin
57
In the cell, what is assemble and disassembly controlled by?
Microtubule-associated proteins
* Allows the cell to control the organization of microtubules
58
# True or False:
Microtubules have structural polarity
True
59
How does structural polarity work in microtubules?
* β-tubulin is exposed at the plus end
* α-tubulin is exposed at the minus end
60
Why is structural polarity important for microtubules?
Crucial for guiding motor proteins (intracellular transport)
61
# True or False:
The plus end is less dynamic
False, it is more dynamic (rates of assembly and disassembly are higher the plus end)
62
When microtubules assemble/disassemble, what happens?
Addition or loss of tubulin subunits
63
# True or False:
Dynamic instability of microtubules can be experimentally altered using drugs
True
64
What effect do Microtubule-stabilizing drugs have?
Prevents depolymerization
65
1. Give an example of a Microtubule-stabilizing drug
2. State how it works
1. Taxol
2. Used in treatment of various cancers, as stabilization of microtubules can prevent cell division
66
What effects do Microtubule-detabilizing drugs have?
Inhibit polymerization (e.g. by binding/sequestering or modifying free tubulin dimers)
67
Give examples of Microtubule-destabilizing drugs
* Colchicine
* Colcemid
* Binblastine
* Vincristine
68
Free tubulin dimers and microtubules exist in an -----------, with growth or shrinkage of the microtubule occuring depending on the ------------- of available -------
* Equilibrium
* Concentration
* Tubulin
69
# Define:
Critical Concentration
| (Microtubules)
The concentration of tubulin at which net growth/shrinkage is zero
(Can also be applied to actin polymerization and depolymerization)
70
Most differentiated animal cells have structural and functional polarity, which reflects the...
Asymmetry of the microtubule array (network)
71
Certain microtubule-associated proteins may stabilize the ---- ends of microtubules, or cause them to form -------
* Plus
* Bundles
72
How can stabilized microtubules maintain organization within the cell?
By transporting or positioning organelles, vesicles etc.
73
What are actin filaments involved in?
| (3 points)
* Involved in cellular movements
* Required for phagocytosis
* Required for cell division
74
Where are actin filaments usually located?
Just below the cell membrane
75
# True or False:
Actin filaments are the smallest of the cytoskeletal components
True (~6 nm in diameter)
76
# True or False:
Actin microfilaments are polar but they do not have dynamic instability
False, they are polar AND they can assemble and disassemble (dynamic instability)
77
What is f-actin? What is it composed of?
Filamentous actin
* Composed of monomers of globular actin (g-actin)
78
# State:
Actin filament functions
| (4 points)
* Structural support
* Movement of organelles and vesicles
* Cell division
* Muscle contraction
79
# Forming an Actin Filament:
What is free floating actin called?
G-actin
80
# Forming an Actin Filament:
How does a filament of actin form?
When ADP becomes ATP, it triggers formation of the filament called F-actin
81
# True or False:
In forming an actin filament, the plus end is the growing end
True
82
What is the role of the minus end in forming an actin filament?
Shrinking end
* Where ATP is hydrolyzed to ADP
83
Actin monomers are bound to ---, which is ---------- to --- following incorporation into the -------------
* ATP
* Hydrolyzed
* ADP
* Microfilament
84
What is the plus end of an actin microfilament characterized by?
A higher rate of growth
85
# True or False:
Both the plus and minus ends of actin microfilaments can polymerize
True, if the concentration of actin monomers is sufficiently high
86
Are actin microfilaments bigger or smaller than the other cytoskeletal components?
Smaller (5-9 nm)
87
# In Actin microfilaments:
----- and associated ------ ------ form a ----------- ---- during -----------
* Actin
* Myosin motors
* Contractile ring
* Cytokinesis
88
# Define:
Treadmilling
| (Actin microfilaments)
An equilibrium state in which monomers are lost from the minus end, while (other) monomers are added to the plus end (also occurs in microtubules)
89
What happens at the plus end of actin microfilaments?
Actin-ATP monomers binds to the growing microfilament faster than ATP in subunits of the existing microfilament is hydrolyzed
90
What happens at the minus end of actin microfilaments?
Actin-ATP is hydrolyzed faster than new actin-ATP monomers can be added
91
When does the actin microfilament stay the same length?
When the rate of loss at the minus end and the rate of gain at the plus end are equal
92
Actin-targeted drugs can alter...
The dynamic behaviour of actin microfilaments
93
# Define and give example(s) of:
Polymerization-inhibiting drugs
Bind/sequester free actin, or cap the plus end
* Latrunculin (binds free actin)
* Cytochalasin (caps plus end)
94
# Define and give example(s) of:
Microfilament-stabilizing drugs
Prevent depolymerization
* Phalloidin
95
Actin-binding proteins can also...
Alter the dynamicity and organization of actin microfilaments
96
# Define and give example(s) of:
Monomer-sequestering proteins
Bind free actin, preventing polymerization
* Thymosin
97
# Define and give example(s) of:
Nucleating proteins
Initiate microfilament formation/polymerization
* No equivalent to an MTOC, so actin microfilaments are nucleated at multiple sites in the cell
* Arp2/3
98
# Define:
Severing proteins
Sever microfilaments into smaller fragments
99
# Define:
Bundling proteins
Link together parallel microfilaments to form bundles
100
# Define:
Cross-linking proteins
Link together perpendicular microfilaments to form a network
101
# Define:
Capping proteins
Bind to the plus end, blocking polymerization
102
# List:
Actin-targeted drugs
| (2 points)
* Polymerization-inhibiting drugs
* Microfilament-stabilizing drugs
103
# List:
Actin-binding proteins
| (7 points)
* Monomer-sequestering proteins
* Nucleating proteins
* Severing proteins
* Bundling proteins
* Cross-linking proteins
* Capping proteins
* Side-binding proteins
104
# Define:
Side-binding proteins
Bind along the side (rather than the ends) of a microfilament
105
# True or False:
Actin may organize into different types of arrays
True
106
How does actin organize into different types of arrays?
Basaed on linking of F-actin by different actin-binding proteins
107
What arrays may actin organize into?
* Parallel bundles
* Contractile bundles
* Cross-linked gel
108
# Describe:
Parallel bundles
| (Actin)
Linked by fimbrin
* In filopodia, microvilli
109
# Describe:
Contractile bundles
| (Actin)
Arranged in an antiparallel manner
* Linked by α-actinin and other proteins
* In stress fibres, contractile ring
110
# Describe:
Cross-linked gel
| (Actin)
Random orientation of F-actin
* Linked by filamin
* Found at the cell cortex
* Involved in amoeboid motion and cytoplasmic streaming
111
What is gelsolin?
An enzyme
* Can break up actin gels
112
# Define:
Cell cortex
A region just beneath the plasma membrane
113
What is the function of actin in the cell cortex?
Provides support/mechanical strength for the plasma membrane
114
# True or False:
Actin in the cell cortex influences cell shape
True (e.g. in red blood cells)
115
What are integrins?
Integrins anchor internal F-actin to the extracellular matrix
116
How many related processes are essential for actin-mediated cell movement?
Three
117
What are the 3 related processes essential for actin-mediated cell movement?
1. The cell pushes out protrusions at the leading edge of the moving cell
2. Protrusions adhere to a surface, providing anchor points
3. Using the integrin anchors, the cell drags itself forward
118
# Define:
Lamellipodia
Thin, sheet-like protrusions
* Contain a branched network of microfilaments
* Oriented such that the plus ends are close to the plasma membrane
119
# In actin-mediated cell movement:
What directs actin branching?
Nucleating and side-binding proteins
120
# In actin-mediated cell movement:
* Plus ends are protected by...
* Minus ends are...
* Plus ends are protected by *capping proteins*
* Minus ends are *severed*
121
# In actin-mediated cell movement:
What results from plus end capping and minus end severing?
Actin network and the membrane are pushed forward
122
# Define:
Filopodia
Thin, rod-like protrusions
* Contain parallel bundles of microfilaments
123
# In actin-mediated cell movement:
What do filopodia rely on?
Formins
* Promotes linear growth instead of branching
124
# In actin-mediated cell movement:
What helps the cell detach and move?
Contractile bundles in the body of the cell
125
# In actin-mediated cell movement:
What is contraction mediated by?
Myosin II
126
# In actin-mediated cell movement:
What is the function of Lamellipodia and Filopodia in cell movement?
"Explore" for a favourable contact point
127
# In actin-mediated cell movement:
What happens when a protrusion makes contact with a favourable surface?
Integrins create an anchor
128
What is chemotaxis?
When environmental factors trigger cell movement
129
What is chemotaxis mediated by?
Rho proteins
130
Rho proteins are a type of...
Ras GTPase
131
What are the Rho proteins that mediate chemotaxis?
1. Cdc42
2. Rac
3. Rho
132
What is the function of Cdc42 in chemotaxis?
Triggers filopodia formation
133
What is the function of Rac in chemotaxis?
Triggers lamellipodia formation
134
What is the function of Rho in chemotaxis?
Activates fiber formation and contractile movement
135
Rho proteins activate...
Genes and proteins involved in different types of cell movement
