Topic 13: Cytoskeleton and Cell Movements Flashcards
1
Q
Cytoskeleton
A
- consists of a network of protein filaments extending throughout the cytoplasm of all eukaryotic cells
2
Q
Structure/Organization of Actin Filaments
A
- Actin: predominant cytoskeleton protein of cells
- amino acid sequence of actin are highly homologous between species
- consists of F Actin
3
Q
Filamentous (F) Actin
A
- thin, flexible filaments approx. 7nm in diameter and up to several micrometers in length
- consist of head to tail arrangement of actin monomers know as Globular (G) Actin
- actin polymerization is reversible (non-covalent)
4
Q
Actin Filaments
A
- microfilaments
- traverse throughout the cytoplasm of a cell
- pointed end = neg. end
- barbed end = + end
- -> rapid monomer addition
5
Q
Globular Actin
A
- an actin monomer that has tight binding sites that mediate head-to-tail interactions with other actin monomers
6
Q
Filamentous Actin
A
- a series of actin monomers that have been polymerized into filaments (helical structure)
7
Q
Polymerization
A
- reversible
- filaments can depolymerize by the dissociation of actin subunits, allowing actin filaments to be broken down when necessary
- can happen without ATP
8
Q
Role of ATP in Microfilament Polymerization
A
- polymerization occurs faster
- ATP-actin = associates with filaments more readily than ADP-actin
- ADP-actin = dissociates from filaments more readily than ATP-actin
9
Q
Treadmilling
A
- occurs in vitro at equilibrium rate of addition and removal of monomers
10
Q
Monomer Association/Dissociation In Vivo in Cytoplasm
A
- critical for formation of cell projections and cell movement
- regulated by actin-binding proteins in vivo, such that stability/instability of actin filaments can vary tremendously depending on cell need
11
Q
Initiation of Actin Filaments
A
- initial polymerization of 3 actin monomers is rate limiting step
- catalyzed by FORMIN
- PROFILIN stimulates the exchange of ADP for ATP
- -> associated with formin
12
Q
Branching of Actin Filaments
A
- Formin and Arp 2/3 complex add actin monomers to the barbed end of actin chain
- causes branching
13
Q
Higher Order Actin Filament Organizations
A
- Actin Network
2. Actin Bundles
14
Q
Actin Network
A
- the actin filaments are cross-linked in orthogonal arrays that form 3D meshwork’s with the properties of semisolid gels
15
Q
Actin Bundles
A
- actin filaments are cross-linked into closely packed arrays
- ex) microvilli in intestinal epithelial cells contain parallel arrays of actin filaments
16
Q
Actin-Bundling Proteins
A
- small rigid proteins that force the cross-linked actin filaments to align closely with one another in bundles
- alpha actinin, fimbrin
17
Q
Alpha Actinin
A
- in contractile bundles
- bundles are more widely spaced to allow for contraction
18
Q
Fimbrin
A
- in non-contractile bundles
19
Q
Actin-Network Forming Proteins
A
- have 2 flexible arms that interact with separate actin filaments
- ex) filamin
- forms a mesh like structure
20
Q
Glycophorin
A
- associated with actin cytoskeleton network immediately underlying plasma membrane
- spectrin and actin together form the cortical cytoskeleton
- ex) red blood cell cortical cytoskeleton
21
Q
Microvilli
A
- fingerlike extensions of the plasma membrane
- abundant on the surface of cells
- involved in absorption
- epithelial cells lining the intestine
22
Q
Actin-Filaments in Cell-ECM Associations
A
- most cells have specialized regions of p. membrane that form contacts with adj. cells (ECM) or other substrata
23
Q
Stress Fibres
A
- bundles of contractile actin filaments in many cell types
- allow cell to exert force against the substratum through cell-extracellular matrix junctions
24
Q
Actin Microfilaments
A
- determination of cell shape
- providing structural support
- important role in formation of cell projections and cell motility
25
Q
Cell Migration Requires
A
- Actin cytoskeleton growth and branching at leading edge (actin-binding proteins)
- Dissociation of focal adhesions at trailing edge and formation of new focal adhesions at leading edge
- Actin cytoskeleton contraction at trailing edge (actin/myosin interaction)
26
Q
Myosin
A
- a protein that interacts with actin
- acts as a molecular motor
27
Q
Molecular Motor
A
- a protein that converts chemical energy in the form of ATP to mechanical energy
- generating force and movement
28
Q
Contractile Properties
A
Actin-Myosin Interactions
29
Q
Types of Myosin
A
- several diff. types depending on cell type
- all are polarized molecules with structurally and functional distinct head and tail regions
- Myosin head acts as hinge that pulls along actin filaments
30
Q
Cell Migration
A
- actin filament contraction
- action of polymerization/branching and retraction of trailing edge through actin depolymerization
- -> cell “pulls” itself” forward at focal adhesions
31
Q
Components necessary for remodelling
A
- Rho stimulates WASP proteins which stimulate Arp2/3 complex
- Rho stimulates formin and profiling
32
Q
Cofilin
A
- actin binding proteins
- severs existing actin filaments
- result in growth of 2 filaments from an existing one
33
Q
Actin Polymerization and Remodelling
A
- response to cell signalling from other cells or the environment
34
Q
Intermediate Filaments
A
- providing mechanical strength to cells and tissues
- form a scaffold to assist in localization of cell process
- essential for maintaining tissue organization and mitigating the impact of external forces on cell sheets
35
Q
Keratins
A
- type of intermediate filament protein of epithelial cells
36
Q
Vimentin
A
- forms a network extending out from the nucleus toward cell periphery
37
Q
Desmin
A
- specifically expressed in muscle cells
- connects contractile elements
38
Q
Neurofilament Proteins
A
- form major intermediate filaments of many types of mature neurons
39
Q
Structure of IFs
A
- central alpha helical rod
N terminus (head)
C terminus (tail) - no polarity
40
Q
Plakins
A
- a family of proteins that bind intermediate filaments and link them to other cellular structures
- ex) cadherins, desmoglein and desmocollin (desmosome)
41
Q
Plectin
A
- also a type of plakin that links IFs to interns of hemidesmosome
42
Q
Microtubules
A
- rigid hollow rods
- determine cell shape
- involved in a variety of cell movements
43
Q
Tubulin
A
- protein that polymerizes to form microtubules
- 1 alpha + 1 beta isoform = tubulin dimer
- have polarity
44
Q
GTP in Microtubule Polymerization
A
- GDP bound tubulin readily dissociate from minus end (must be protected in cell)
45
Q
Dynamic Instability
A
- behavior in which individual microtubules alternate between cycles of growth and shrinkage at the plus end
- Dependent on rate of GTP hydrolysis at plus end of microtubule, and free pool of GTP bound tubulin dimers
46
Q
Colchicine and Colcemid
A
- experimental drugs
- bind tubulin and inhibit microtubulin polymerization (blocks mitosis)
47
Q
Vincristine and Vinblastine
A
- drugs used in chemotherapy
- inhibit microtubule polymerization (blocks mitosis)
48
Q
Taxol
A
- a drug that stabilizes microtubules
- blocks cell division
49
Q
3 Categories of MAPs
A
- growth (polymerase)
- Shrinkage or catastrophe (depolymerase)
- Rescue (CLASP protein)
50
Q
Centrosome
A
- the microtubule-organizing center in animal cells
- anchoring point of minus end of most microtubules
- initiates microtubule growth
51
Q
Structure of Centrosomes
A
- pair of centrioles anchored perpendicular to each other within amorphous pericentriolar material
- pericentriolar material initiates microtubule assembly
52
Q
Kinesins
A
- motor proteins that move along microtubules toward plus end and minus end
- depends on cell type and cargo
- specific kinesin involved
53
Q
Dyneins
A
- motor proteins that move along microtubules only toward minus end
54
Q
Head Region
A
- microtubule interaction (motor) domain
- position along N-terminal/C-terminal length
- determines direction
55
Q
Tail Regions
A
- cargo/organelle interaction domain
- specificity determined by primary amino acid sequence and 2nd structure
56
Q
Axoneme
A
- the fundamental structural unit of organization of both cilia and flagella
- composed of microtubules and their associated proteins
57
Q
Basal Body
A
- structure similar to a centriole that initiates the growth of axonemal microtubules
- anchors cilia and flagella to the rest of the cell
58
Q
Cross-Sectional Structure of Cilia and Flagella
A
9+2 pattern
59
Q
Cilia and Flagella Movement
A
- dynein is responsible for movement
- result from the sliding of outer microtubule doublets
- powered by motor activity of axonemal dyneins
- requires precise coordination
60
Q
Microtubules during Mitosis
A
- centrioles and other components of the centrosome are duplicated
- move to opposite poles
- mitotic spindles are responsible for separating daughter chromosomes
- Dynamic instability of microtubules is very important for the mitotic process
61
Q
mitotic spindles
A
- array of microtubules extending from the spindle poles
62
Q
Kinetochore Microtubules
A
- attach to the condensed chromosomes of mitotic cells at their centromeres
63
Q
Chromosomal Microtubules
A
connect to the ends of the chromosomes via chromokinesin
64
Q
Astral Microtubules
A
- extend outward from the centrosomes to the cell periphery and contribute to chromosome movement by pushing the spindle poles apart
65
Q
Polar Microtubules
A
- are not attached to chromosomes but are stabilized by overlapping with each other in the center of the cell
- contribute to chromosome movement by pushing the spindle poles apart
66
Q
Anaphase A
A
- movement of chromosomes toward the spindle poles along the kinetochore microtubules
- chromosomal and kinetochore
67
Q
Anaphase B
A
- separation of spindle poles themselves
- polar and astral
68
Q
Chromosome movement
A
- requires minus-end motor proteins and microtubule disassembly
69
Q
Spindle Pole Separation Requires
A
- pulling action of astral microtubules directed by minus-end directed motor proteins anchored to distal region of the cell
- sliding of polar microtubules past each other due to action f +end directed motor proteins
