Cytoskeleton and Cell Movement

Question 1

What is filamentous (F) actin?

Answer 1

Thin, flexible filaments that consist of head to tail arrangements of monomers known as globular (G) actin.

Question 2

What is globular (G) actin?

Answer 2

An actin monomer that has tight binding sites that mediate head-to-tail interactions with other actin monomers.

Question 3

What is the polarity of actin filaments? (pointed vs barbed end)

Answer 3

• Pointed end: negative (slow monomer addition)

- Barbed end: positive (rapid monomer addition)

Question 4

How can filaments depolymerize?

Answer 4

By the dissociation of actin subunits, allowing actin filaments to be broken down when necessary.

Question 5

When does treadmilling occur? How does it occur?

Answer 5

When globular actin is limited. Actin will continue to grow at the barbed end using monomers that have disassociated from the pointed end.

Question 6

Where does monomer association/disassociation occur? What is it critical for? What is it regulated by?

Answer 6

• occurs in the cytoplasm
• critical for formation of cell projections and cell movement
• regulated by actin-binding proteins

Question 7

How are actin networks formed?

Answer 7

actin filaments are cross-linked in arrays that form 3D meshworks with the properties of semisolid gels

Question 8

How are actin bundles formed?

Answer 8

Actin filaments are cross-linked into closely packed bundles

Question 9

What are actin-bundling proteins?

Answer 9

Small rigid proteins that force the cross-linked actin filaments to align closely with one another in bundles

Question 10

What is the structure of actin-network forming proteins?

Answer 10

They have two flexible arms that interact with separate actin filaments to form a mesh like structure

Question 11

Where is the cortical cytoskeleton located?

Answer 11

immediately under the plasma membrane

Question 12

Which proteins work together with actin to form the cortical cytoskeleton? What do they do?

Answer 12

Ankyrin, spectrin, and protein 4.2 work with actin to form the cortical cytoskeleton and attach it to key integral membrane proteins

Question 13

What do cell movement and the extension of long cellular processes require? (2 things)

Answer 13

1. actin cytoskeleton growth and branching by polymerization at the leading edge
2. disassociation of focal adhesions at the trailing edge and the formation of new focal adhesions at the leading edge

Question 14

What is myosin?

Answer 14

A protein that interacts with actin and acts as a molecular motor.

Question 15

What is a molecular motor?

Answer 15

A protein that converts chemical energy in the form of ATP to mechanical energy, thus generating force and movement.

Question 16

What is the function of the protein Rho?

Answer 16

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.

Question 17

What is cytokinesis?

Answer 17

The division of a cell into two cells following mitosis

Question 18

What do intermediate filaments play a role in?

Answer 18

Play a structural role by providing mechanical strength to cells and tissues

Question 19

What do intermediate filaments form?

Answer 19

A scaffolding to assist in localization of cell processing

Question 20

What are the 5 intermediate filament proteins?

Answer 20

1 &2. keratins (epithelial cells)

3. vimentin (forms a network extending out from the the nucleus to the cell periphery) and desmin (connects contractile elements)
4. neurofilament proteins (mature neurons)
5. nuclear lamins

Question 21

How are the tetramers of intermediate filaments arranged?

Answer 21

Arranged in antiparallel manner (N terminus to C terminus)

Question 22

How are desmosomes formed?

Answer 22

Intermediate filaments are linked to other cellular structures such as the cadherins, desmoglein, and desmocollin through intermediary proteins.

Question 23

How are hemidesmosomes formed?

Answer 23

Intermediate filaments are linked to Laminin by integrins through intermediary proteins

Question 24

what are microtubules?

Answer 24

Rigid hollow rods that determine cell shape and are involved in a variety of cell movements.

Question 25

What is tubulin?

Answer 25

A protein that polymerizes to form microtubules.

Question 26

How does tubulin form microtubules?

Answer 26

One alpha and one beta isoform combine to form a tubulin dimer which polymerizes to form microtubules.

Question 27

What is the polarity of microtubules? (alpha tubulin vs beta tubulin)

Answer 27

Alpha tubulin faces the plus end (fast growing)

Beta tubulin faces the minus end (non growing)

Question 28

What is dynamic instability? What is it dependent on?

Answer 28

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

Question 29

What are colchicine and colcemid?

Answer 29

Drugs that bind tubulin and inhibit microtubule polymerization, which in turn blocks mitosis

Question 30

What are vincristine and vinblastine?

Answer 30

Drugs that are used in cancer chemotherapy, and inhibit microtubule polymerization which blocks mitosis and cell division

Question 31

What is taxol?

Answer 31

A drug that stabilizes microtubules, rather than inhibiting their assembly, which also blocks cell division.

Question 32

What is a centrosome?

Answer 32

The microtubule-organizing centre in animal cells and the anchoring point of the minus end of most microtubules.

Question 33

What do centrosomes initiate?

Answer 33

initiate microtubule growth, which grow out at the plus end.

Question 34

What do centrosomes consist of?

Answer 34

A pair of centrioles anchored perpendicular to each other within amorphous pericentriolar material.

Question 35

What are microtubules responsible for?

Answer 35

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.

Question 36

What are kinesins?

Answer 36

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.

Question 37

What are dyneins?

Answer 37

motor proteins that move along microtubules toward the minus end

Question 38

What is the basal body?

Answer 38

Structure similar to a centriole that initiates the growth axonemal microtubules and anchors cilia and flagella to the rest of the cell.

Question 39

What is the axoneme?

Answer 39

the fundamental structural unit of organization of both cilia and flagella

Question 40

What are kinetochore microtubules?

Answer 40

Microtubules that attach to the condensed chromosomes of mitotic cells at their centromeres

Question 41

What are astral microtubules?

Answer 41

Microtubules that extend outward from the centrosomes to the cell periphery and contribute to chromosome movement by pulling the spindle poles apart

Question 42

What are polar microtubules?

Answer 42

Microtubules that are not attached to chromosomes but are stabilized by overlapping with each other in the centre of the cell.

Question 43

What do polar microtubules contribute to?

Answer 43

Chromosome movement by pushing the spindle poles apart.

Question 44

What is anaphase A? What does it involve?

Answer 44

The movement of chromosomes toward the spindle poles along the kinetochore microtubules.
Involves chromosomal and kinetochore microtubules.

Question 45

What is anaphase B? What does it involve?

Answer 45

The separation of the spindle poles themselves.

Involves polar and astral microtubules.

Question 46

What does chromosome movement at the plus end require? (2 things)

Answer 46

1. minus-end-directed motor proteins that are part of the kinetochore
2. microtubule disassembly

Question 47

What does spindle pole separation require? (2 things)

Answer 47

1. pulling action of astral microtubules directed by minus-end directed motor proteins anchored to the distal region of the cell.
2. sliding of polar microtubules past each other due to action of plus-end directed motor proteins.