(Damjanovski) Lecture 8 Flashcards
(101 cards)
1
Q
What do actin/myosin contractile ring structures look like?
A
Sarcomeres
* Depolymerize to separate the 2 cells
2
Q
Where do stress fibers appear in?
A
Migrating cells
3
Q
True or False:
Smooth muscle contraction is non-voluntary
A
True
4
Q
How does long contraction myosin get activated?
A
Ca2+ ions activate MLC kinase
* Phosphorylation of Myosin LC makes it become active
5
Q
What type of myosin is present in smooth muscle cells?
A
Long contraction myosin
6
Q
Smooth muscles lack….
A
Troponin and tropomyosin
7
Q
How does Ca2+ alter myosin conformation?
A
Calmodulin (CaM)
8
Q
Where does phosphorylation occur on the long contraction myosin?
A
Light chains
9
Q
What transports vesicles along actin filaments?
A
Myosin V
10
Q
What is transported in the vesicles by myosin V?
A
- Vesicles
- mRNA
11
Q
How is the nucleus positioned/repositioned by actin?
A
Microtubles are carried by myosin along actin, dragging the nucleus
12
Q
True or False:
Myosin V is always active
A
False, it is inactive in the absence of cargo
13
Q
Cytoplasmic streaming
A
Movement of cytoplasm in plants helping with diffusion
14
Q
How is cytoplasmic streaming performed?
A
Myosin V carrying the cytoplasmic components along the actin filaments near the cell membrane/wall
15
Q
True or False:
Adult cells usually don’t move
A
True
16
Q
What structures are present in migrating cells formed by actin?
A
- Stress fibers
- Lamellopodia
- Fillipodia
17
Q
Stress fibers connect to the extracellular matrix via…
A
Focal adhesions with Integrins
18
Q
Chemotaxis
A
Chemical signals that attract cells
19
Q
What is key everywhere on a cell surface to respond to chemical signals?
A
- Receptors
- G proteins
20
Q
What do cells like/will move towards?
A
cAMP
21
Q
Cell movement:
Extension
A
Actin polymerization extends the cell forwards in direction movement
22
Q
Cell movement:
Adhesion
A
New focal adhesion formed
23
Q
Cell movement:
Translocation
A
Stress fiber contraction will move the cell forward
24
Q
Cell movement:
De-adhesion
A
Old focal adhesion is released
25
What are the Rho proteins important in cell migration?
* RhoGTP
* Rac
* Cdc42
26
Initially, what 2 Rho proteins work together?
Cdc42 and Rac
27
What is Cdc42 responsibility in cell migration?
Cdc42 (GTP) activates Par6 and WASp
* Par6 helps determine polarity (front end of the cell)
* WASp activates Arp 2/3
Result: Actin polymerization = Filipodia formation
28
What is Rac responsibility in cell migration?
Rac (GTP) activates WAVE
* WAVE activates Arp 2/3
Result: Actin polymerization = Lamellipodia formation
29
After inital steps, what does Cdc42 and Rac help trigger?
Rho activation
30
What is Rho responsibility in cell migration?
Rho (GTP) activates Formin and Rho kinase
* Rho kinase phosphorylates Myosin LC, providing myosin activity
* Formin helps with actin polymerization
Result: Myosin activity + Actin polymerization = Stress fiber formation and contraction
31
# True or False:
All Cdc42, Rac, and Rho are required for effective migration
True, demonstrated in a scratch assay
32
Which of the Rho proteins are important for polarity?
Cdc42
33
How does Cdc42 activation ensure polarity?
1. Cdc42 activation at the front triggers Rac activation at the front
2. Rac activation at the front triggers Rho activation at the back
3. This inhibits Rac activation at front
34
What does Par6 do?
1. Microtubule (+) end capture
2. Dynein activation
Tells cell contents to go towards a certain direction (the front end)
35
5 key points on intermediate filaments
1. Not globular
2. No ATP/GTP needed
3. No polarity
4. No known motor proteins
5. Less dynamic
36
What is the main role of intermediate filaments?
Great tensile strength, for cell and tissue integrity
37
Basic subunit of an intermediate filament is a...
Tetramer
* 2 dimers together
* No polarity as the the C terminus of 1 dimer is with the N terminal of the other dimer
38
Classes of intermediate filaments and the associated cells
1. **Keratin** - Epithelial cells
2. **Desmin** - Muscle cells
3. **Vimentin** - Migrating cells
4. **Neurofilaments** - Neurons
5. **Lamin** - Nucleus
39
What do lamins support?
Inner nuclear membrane
40
What proteins link intermediate filaments to other structures such as microtubules?
Plectin
41
Vimentin links to what at the plasma membrane?
Ankyrin
42
What are the lamins that support the nuclear membrane?
Lamins A, B, and C
43
How are lamins A, B and C linked to the nuclear membrane?
Prenylation
44
How are intermediate filaments (lamins) linked to cytoplasmic cytoskeletal protein?
LINC complexes
45
When do intermediate filaments need to be disassembled?
During mitosis
46
What signal tells intermediate filaments to disassemble?
N terminal domain of lamin A phosphorylated at serine
* Induces disassembly and prevents reassembly
47
If phosphorylation is key in disassembly and reassembly, what protein must be required?
CDKs
48
In epithelial cells, what are intermediate filaments anchoredto?
Desmosomes
Hemidesmosomes
49
Desmosomes
Cell to cell
50
Hemidesmosomes
Extracellular Matrix to Cell
51
Desmosomes and hemidesmosomes only occur in...
Epithelial cells
52
What do desmosomes and hemidesmosomes link to in the cell?
Intermediate filaments
53
What are the 4 types of cell adhesions?
1. Gap junctions
2. Tight junctions
3. Cell-cell adhesions
4. Cell-ECM adhesions
54
What are gap junctions for?
Allow passage and communication via small molecules
55
What are gap junctions comprised of?
Connexins
* 6 connexins = 1 connexon
56
How many connexins form a channel in a gap junction?
12
57
Are all connexins the same?
No, different connexins can form channels of different sizes and allow different ions through
58
What will trigger the closing of a gap junction?
Cytoplasmic Ca2+
59
Tight junction purpose
Barrier forming
60
Where are tight junctions present?
Near the apical surface of epithelial cells
61
Are gap junctions present in all cells?
Yes
62
What proteins are involved in the formation of a tight junction?
1. JAM
2. Occludin
3. Claudin
63
What pathway do tight junctions prevent from occurring?
Paracellular pathway
64
CAMs
Cell Adhesion Molecules
65
CAMs with homophilic interactions
1. Cadherins
2. Ig Superfamily
66
CAMs with heterophilic interactions
1. Integrins
2. Selectins
67
What can homophilic interactions bind to?
Same molecules
(Cell to cell)
68
What can heterophilic interactions bind to?
Different molecules
* Cell to cell OR Cell to ECM
69
What are characteristics of CAMs?
Transmembrane proteins
* Cytoplasmic domain works with cytoskeleton
70
How many types of cadherins are there?
Over 40
71
Structure of cadherins
* Single transmembrane domain
* Cytosolic C-terminal tail (associated with cytoskeleton)
72
What is the important role of cadherins?
Holding cells in sheets
73
E cadherin...
Epidermal tissues
74
N-cadherin
Nervous tissues
75
Cadherin - F actin =
Circumferential belt, Adherens junction
76
Cadherin - keratin =
Desmosome
77
Cell adhesion structures connect to cytoskeletal components via...
Adaptor proteins
* Monitor cell adhesion
* Can signaling
78
What is one adaptor protein we talked about?
Catenins (beta catenin etc.)
79
What are the 5 main roles of ECM?
1. Anchoring and surrounding cells to maintain solid-tissue 3D architecture
2. Controlling cellular polarity, survival, proliferation, differentiation and fate
3. Inhibiting of facilitating cell migration
4. Binding to and acting as a reservoir or growth factors
5. Activating cell surface signaling receptors
80
ECM proteins can be...
1. Hydrophilic
2. Structural
3. Adhesive
81
Hydrophilic ECM proteins
Proteoglycans
82
Structural ECM proteins
Collagens
83
Adhesive ECM proteins
Fibronectin, laminin
84
Proteoglycans
* Structure
* Where would you find it
* Lots of sugar groups
* Joint fluid
* Involved in resiliency in tissues
85
Collagens
* Structure
* Where would you find it
* Forms large structures
* Holds cells in structure
86
Laminin and Fibronectin
* Structure
* Where would you find it
* Cell sticking and migration
* Development
87
Integrin
Heterodimeric transmembrane protein (alpha and beta)
88
How can integrin bind to specific substrates?
Different alpha and beta combinations
89
Integrins bind to...
RGD sequences
90
# True or False:
Integrins require only the RGD sequence to bind
Requires nearby synergy regions for specificity
91
1. alpha1beta1 binds...
2. alpha5beta1 binds...
3. alpha6beta1 binds...
1. Collagen
2. Fibronectin
3. Laminin
92
Fibronectin - Integrin - F-actin
Focal adhesion
93
Laminin - Integrin - Keratin
Hemidesmosomes
94
Are integrins active the entire time?
No, it has active and inactive states
95
What do selectins recognize?
Oligosaccharides
96
What selectin did we talk about in class and what does it participate in?
P-selectin
* Participates in leukocyte extravasation
97
What sends the signal for P-selectin to appear?
Pathogens causing signals
98
How does the p-selectin travel to the surface?
Pathogen signal causes p-selectin to be transported to surface through vesicle
99
What does p-selectin do?
Sticks to carbohydrates on leukocyte
100
What happens after leukocyte sticks to p-selectin?
PAF receptor binds to PAF, activating integrin
101
What does the activate integrin on leukocytes bind to?
ICAM
