Lecture 10

Question 1

Cytoskeleton does what?

Answer 1

1. impart cell shape
2. internal organization
3. enhance cell function

Question 2

Cytoskeletal filaments in general:

Answer 2

1. self-assembles from smaller subunits
2. polar (exception: intermediate filaments)
3. highly dynamic and versatile (structure and function can be modified, ant’s trail)

Question 3

Actin filament structure

Answer 3

1. helical polymer of g-actin

2. flexible = 8 nm

Question 4

Actin filament assembles into?

Answer 4

1. bundles
2. 2D networks
3. 3D gels

Question 5

Actin functions

Answer 5

1. cell surface shape
2. whole cell locomotion
3. cytokinesis

Question 6

Cortical actin

Answer 6

underlies plasma membrane to impart shape and strength in lipid bilayer

Question 7

Actin polymerization

Answer 7

drives outgrowth of surface projections

• dynamic: lamellipodia with filopodia
• stable: stereocilia, microvilli

Question 8

actin bundles

Answer 8

allow cells to resist force (stress fibers) or to generate force (thin filament in muscle sarcomere)

Question 9

Actin causes what in plant cells?

Answer 9

cytoplasmic streaming

Question 10

Microtubule structure

Answer 10

• Polymer of α- and β-tubulin (Ø 25 nm)
• Dynamic array extending from MTOC
  or
  Bipolar mitotic spindle
• Supports outgrowth of cilia
• Extensively bundled in axons

Question 11

Microtubule functions

Answer 11

• Intracellular transport and positioning
  of organelles, vesicles, and
  macromolecules
• Chromosome segregation
  (as mitotic spindle)
• Directs synthesis of cell wall (in plants)
• More literally a skeleton in protozoa

Question 12

Intermediate filaments structure

Answer 12

• Fiber made from intermediate filament proteins

- Highly flexible, rope-like filament (Ø 10 nm)

Question 13

Intermediate filament functions

Answer 13

• Imparts toughness to cells
• Forms the nuclear lamina
• Extends across the cytoplasm as
  stable cable
• Connects cell junctions in epithelia
• Enable the formation of tough
  appendages (hair and fingernails)

Question 14

How is cytoskeleton so flexible?

Answer 14

the bones of the cytoskeleton are very flexible (structure and function)

Question 15

How does actin impart cellular organization ?

Answer 15

-constantly turns over even in stable structure (subunits replaced every 48 hrs)

Question 16

Turnover rate of actin, microvilli, stereocilia

Answer 16

• actin - q 48 hrs
• microvilli- few days
• stereocilia - life time

Question 17

Physical and dynamic properties of cytoskeletal filaments allow?

Answer 17

• rapid transport to assembly site

- rapid assembly and disassembly of filament

Question 18

Intermediate filament

Answer 18

• Symmetric, non-polar filament

* Subunits don’t bind NTP

Question 19

Assembly and disassembly of intermediate filaments regulated by?

Answer 19

phosphorylation

Question 20

a-helical coiled coil of intermediate filaments form?

Answer 20

extensive lateral contacts and assemble

into ropes that tolerate stretching and bending

Question 21

Cytoskeleton associated proteins

Answer 21

→ provide cells with highly organized but flexible internal structure
→ control many aspects of filament assembly
→ link filaments to one another, organelles, and the plasma membrane
→ convey intra- end extracellular signals to the filaments
→ participate in or mediate force production