Actin, Intermediate Filaments, Cell Adhesion

Question 1

Smooth Muscle

Answer 1

• phosphorylate myosin light chain = persistent contraction

- regulated by extracellular signals

Question 2

Myosin and Vesicle Transport

Answer 2

• myosin V bound vesicles carried along actin filaments
• actin is capped by formin
• actin pulls on MTs to pull nucleus
• myosin V needs cargo to be active

Question 3

Myosin V and Yeast Budding

Answer 3

• material transported into bud by myosin V
• formin activated at end and entry of bud
• actin added at (+) end = growing

Question 4

Cytoplasmic Streaming

Answer 4

• transport along actin cytoskeleton = cytoplasm move
• used with diffusion in gas exchange
• cortical cytoplasmic actin around plant cell
• myosin V moves organelles along actin

Question 5

Cell Migration

Answer 5

• pushing PM forward b/c actin polymerization
• Leading Edge = filopodia and lamellipodia
• Stress Fibers = focal adhesions (anchors cell to substrate)

Question 6

Chemotaxis

Answer 6

• cells respond to cAMP
• cells have receptor for chemoattractant around cell surface
• activates actin polymerization at leading edge

Question 7

Steps of Cell Movement

Answer 7

• cell on substrate attached to focal adhesions + cAMP

1) Extension = actin polymerization at leading edge
2) Adhesion = lamellipodia forms NEW focal adhesion
3) Translocation = cell moves
4) De-adhesion & Endocytic Recycling = remove old adhesion

Question 8

Signalling Molecules

Answer 8

Rho-GTP ==> formin
Cdc42-GTP ==> activates WASp ==> activate Arp2/3
Rac-GTP ==> activates WAVE ==> activate Arp2/3

Question 9

Mutations to Signalling Molecules

Answer 9

Dominant-active Rho = stress fibers
Dominant-active Cdc42 = lamellipodia
Dominant-active Rac = filopodia

Question 10

Scratch Closure Assay

Answer 10

Cdc42 –> Rac –> Rho –| Rac

• confluent cells scratched = wound
• control = wound closure
• experimental (inactive form ANY signalling molecule) = wound does not close

Question 11

Intermediate Filaments

Answer 11

• not globular
• not need ATP or GTP
• no polarity
• no motor proteins
• tetramer = basic subunit

Question 12

Class I of Intermediate Filaments

Answer 12

acidic keratins
epithelial cells
tissue strength

Question 13

Class II of Intermediate Filaments

Answer 13

basic keratins
epithelial cells
tissue strength

Question 14

Class III of Intermediate Filaments

Answer 14

desmin, GFAP, vimentin
muscle & mesenchymal cells
sarcomere organization

Question 15

Class IV of Intermediate Filaments

Answer 15

neurofilaments
nucleus
axon organization

Question 16

Class V of Intermediate Filaments

Answer 16

lamins
nucleus
nuclear organization

Question 17

Proteins Associated with Intermediate Filaments

Answer 17

plectin cross-links intermediate filament vimentin and MT

Question 18

Functions of Intermediate Filaments

Answer 18

• structural support for cell (links to PM)

- lamins support nuclear membrane

Question 19

Dynamic State

Answer 19

• proteins within filament are exchanged
• N-terminal domain of lamin A phosphorylated at serine = disassembly and prevents reassembly
• • break nuclear membrane –> mitotic apparatus

Question 20

Tissue Integrity

Answer 20

• transgenic mice w/ mutant keratin gene = skin blistering

- epithelial cells have IF anchored to desmosomes and hemidesmosomes

Question 21

Epithelial Cells Polarity

Answer 21

• apical surface = microvilli

- basal surface = connect to ECM

Question 22

Tight Junctions

Answer 22

• hold cells together to prevent material going through

- rows of occludin, claudin, JAM proteins in each cell

Question 23

Gap Junctions

Answer 23

• hold cells together for communication
• 6 connexins = connexon
• 2 connexons = gap junction channel
• channel closes when exposed to Ca2+

Question 24

Cadherins (Homophilic Interactions)

Answer 24

• single transmembrane domain + cytosolic C-terminal tail
• Ca2+ dependent
• linked to intermediate filament = desmosome
• linked to actin (via adapter proteins) = adherens junction

Question 25

Ig-Superfamily CAMs (Homophilic Interactions)

Answer 25

- mediate Ca2+ independent homophilic interactions

Question 26

Integrins (Heterophilic Interactions)

Answer 26

- heterodimeric transmembrane protein - α1β1 binds collagen - α5β1 binds fibronectin - α6β1 binds laminin - bind to core RGD amino acids

Question 27

Selectins (Heterophilic Interactions)

Answer 27

- leukocyte extravasation (WBC leave bloodstream) - endothelial cells secrete P-selectin and PAF - P-selectin binds to oligosaccharides on leukocyte - PAF binds to PAF receptor on leukocyte -- activate integrin - integrin binds to ICAM - push endothelial cells apart and enter

Question 28

Extracellular Matrix Proteins

Answer 28

``` Proteoglycans = hydrophilic (absorb water) Collagen = structural (strength) Laminin = adhesive (recognized by integrins) Fibronectin = adhesive (recognized by integrins) ```

Question 29

Extracellular Matrix Functions (5)

Answer 29

- anchor + surround cells ---> shape - control cell polarity, survival, differentiation - inhibit/facilitate cell migration - binding growth factors - activating cell surface receptors

Question 30

Integrins + Extracellular Matrix

Answer 30

Bind to ECM Cytoskeleton (actin = stress fiber) (IF = hemidesmosome) Active form to bind to substrate - inactive not bind to RGD