Cytoskeleton and Cell Movement Flashcards
What is filamentous (F) actin?
Thin, flexible filaments that consist of head to tail arrangements of monomers known as globular (G) actin.
What is globular (G) actin?
An actin monomer that has tight binding sites that mediate head-to-tail interactions with other actin monomers.
What is the polarity of actin filaments? (pointed vs barbed end)
- Pointed end: negative (slow monomer addition)
- Barbed end: positive (rapid monomer addition)
How can filaments depolymerize?
By the dissociation of actin subunits, allowing actin filaments to be broken down when necessary.
When does treadmilling occur? How does it occur?
When globular actin is limited. Actin will continue to grow at the barbed end using monomers that have disassociated from the pointed end.
Where does monomer association/disassociation occur? What is it critical for? What is it regulated by?
- occurs in the cytoplasm
- critical for formation of cell projections and cell movement
- regulated by actin-binding proteins
How are actin networks formed?
actin filaments are cross-linked in arrays that form 3D meshworks with the properties of semisolid gels
How are actin bundles formed?
Actin filaments are cross-linked into closely packed bundles
What are actin-bundling proteins?
Small rigid proteins that force the cross-linked actin filaments to align closely with one another in bundles
What is the structure of actin-network forming proteins?
They have two flexible arms that interact with separate actin filaments to form a mesh like structure
Where is the cortical cytoskeleton located?
immediately under the plasma membrane
Which proteins work together with actin to form the cortical cytoskeleton? What do they do?
Ankyrin, spectrin, and protein 4.2 work with actin to form the cortical cytoskeleton and attach it to key integral membrane proteins
What do cell movement and the extension of long cellular processes require? (2 things)
- actin cytoskeleton growth and branching by polymerization at the leading edge
- disassociation of focal adhesions at the trailing edge and the formation of new focal adhesions at the leading edge
What is myosin?
A protein that interacts with actin and acts as a molecular motor.
What is a molecular motor?
A protein that converts chemical energy in the form of ATP to mechanical energy, thus generating force and movement.
What is the function of the protein Rho?
Rho is a protein that is stimulated by a signal from the extracellular space. It stimulates actin polymerization and the Arp2/3 complex in wound healing.
What is cytokinesis?
The division of a cell into two cells following mitosis
What do intermediate filaments play a role in?
Play a structural role by providing mechanical strength to cells and tissues
What do intermediate filaments form?
A scaffolding to assist in localization of cell processing
What are the 5 intermediate filament proteins?
1 &2. keratins (epithelial cells)
- vimentin (forms a network extending out from the the nucleus to the cell periphery) and desmin (connects contractile elements)
- neurofilament proteins (mature neurons)
- nuclear lamins
How are the tetramers of intermediate filaments arranged?
Arranged in antiparallel manner (N terminus to C terminus)
How are desmosomes formed?
Intermediate filaments are linked to other cellular structures such as the cadherins, desmoglein, and desmocollin through intermediary proteins.
How are hemidesmosomes formed?
Intermediate filaments are linked to Laminin by integrins through intermediary proteins
what are microtubules?
Rigid hollow rods that determine cell shape and are involved in a variety of cell movements.
What is tubulin?
A protein that polymerizes to form microtubules.
How does tubulin form microtubules?
One alpha and one beta isoform combine to form a tubulin dimer which polymerizes to form microtubules.
What is the polarity of microtubules? (alpha tubulin vs beta tubulin)
Alpha tubulin faces the plus end (fast growing)
Beta tubulin faces the minus end (non growing)
What is dynamic instability? What is it dependent on?
A behaviour in which individual microtubules alternate between cycles of growth and shrinkage at the plus end.
Dependent on the rate of GTP hydrolysis at the plus end and a free pool of GTP bound tubulin dimers
What are colchicine and colcemid?
Drugs that bind tubulin and inhibit microtubule polymerization, which in turn blocks mitosis
What are vincristine and vinblastine?
Drugs that are used in cancer chemotherapy, and inhibit microtubule polymerization which blocks mitosis and cell division
What is taxol?
A drug that stabilizes microtubules, rather than inhibiting their assembly, which also blocks cell division.
What is a centrosome?
The microtubule-organizing centre in animal cells and the anchoring point of the minus end of most microtubules.
What do centrosomes initiate?
initiate microtubule growth, which grow out at the plus end.
What do centrosomes consist of?
A pair of centrioles anchored perpendicular to each other within amorphous pericentriolar material.
What are microtubules responsible for?
A variety of cell movements, including the intracellular transport and positioning of membrane vesicles and organelles, the separation of chromosomes at mitosis, and the beating of cilia and flagella.
What are kinesins?
motor proteins that move along microtubules both toward the plus end or minus end, depending on the cell type and cargo, and the specific kinesin involved.
What are dyneins?
motor proteins that move along microtubules toward the minus end
What is the basal body?
Structure similar to a centriole that initiates the growth axonemal microtubules and anchors cilia and flagella to the rest of the cell.
What is the axoneme?
the fundamental structural unit of organization of both cilia and flagella
What are kinetochore microtubules?
Microtubules that attach to the condensed chromosomes of mitotic cells at their centromeres
What are astral microtubules?
Microtubules that extend outward from the centrosomes to the cell periphery and contribute to chromosome movement by pulling the spindle poles apart
What are polar microtubules?
Microtubules that are not attached to chromosomes but are stabilized by overlapping with each other in the centre of the cell.
What do polar microtubules contribute to?
Chromosome movement by pushing the spindle poles apart.
What is anaphase A? What does it involve?
The movement of chromosomes toward the spindle poles along the kinetochore microtubules.
Involves chromosomal and kinetochore microtubules.
What is anaphase B? What does it involve?
The separation of the spindle poles themselves.
Involves polar and astral microtubules.
What does chromosome movement at the plus end require? (2 things)
- minus-end-directed motor proteins that are part of the kinetochore
- microtubule disassembly
What does spindle pole separation require? (2 things)
- pulling action of astral microtubules directed by minus-end directed motor proteins anchored to the distal region of the cell.
- sliding of polar microtubules past each other due to action of plus-end directed motor proteins.
