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CBNS101 Lecture 13: Cytoskeletal Systems and Polymer Dynamics

front 1

What are the many functions of the cytoskeleton?

back 1

  • Aid in the dividing of cells
  • Aids the intracellular traffic of materials in organelles
  • Supports the plasma membrane frame and allows it to bear stresses and form their shapes
  • Allows cells to swim or crawl
  • Allows contraction within muscles and the extension of axons and dendrites
  • Guides the growth of plant cell wall

front 2

What are the 3 classes of cytoskeletal filaments?

back 2

Microtubules (25nm), Intermediate filaments (10nm), Microfilaments (5-8nm)

front 3

Where are microtubules usually located and what are their functions?

back 3

  • They come from the centrosome by the nucleus (looks like a spider)
  • They determine positions of organelles and direct intracellular transport of materials

front 4

Where are intermediate filaments located and what are their functions?

back 4

  • All all throughout the cytoplasm to form a lamina around the nuclear membrane (confetti filler in the "gift bag")
  • They provide strength and resistance to shear (sliding) stress

front 5

Where are microfilaments located and what are their functions?

back 5

  • They usually line the edges of the cell membrane on the cell periphery (bubble wrap of the intermediate filaments)
  • They determine the shape of the cell's surface and are necessary for whole-cell locomotion

front 6

T/F The cytoskeletal filaments can function on their own without the need of accessory proteins

back 6

False. Accessory proteins are what bind them to each other as well as to other cell components

front 7

What cytoskeletal functions do microtubules play a part in?

back 7

  • Acting as train tracts for material movements and in axons
  • Provide the force for movement \
  • Are mitotic spindles
  • (Think of them as octopus arms managing things on the inside!)

front 8

What are actin filaments a part of?

a) microtubules

b) intermediate filaments

c) mircofilaments

back 8

b) intermediate filaments

front 9

T/F Actin filaments are only in one shape

back 9

False. They can come in a variety of linear bundles like 2D sheets or 3D gels in the cell cortex

front 10

What do a ctin filaments do?

back 10

  • They push and pull to mold the cell into it's shape
  • They also generate force during muscle contractions

front 11

T/F All species have intermediate filaments

back 11

False. Not all species have intermediate filaments because they evolved later down the phylogeny tree

front 12

How do intermediate filaments affect the nucleus?

back 12

They organize the chromatin inside the nucleus to control nuclear disassembly when undergoing mitosis

front 13

T/F The cytoskeleton structures are always stable

back 13

False. They can be both stable or dynamic depending on the cell. A highway or ant trail

front 14

Give an example of a dynamic cytoskeletal structure and a stable cytoskeletal structure

back 14

Dynamic: actin filaments and microtubules when a cell divides

Stable: Skin cells I'm assuming

front 15

T/F Once cytoskeletal filaments are made they cannot be broken down

back 15

False. They can assemble and disassemble depending on what the cell needs

front 16

Fill in the blanks

  • Assembly/disassembly happens at the _______ (end/middle) of the filaments.
  • The process occurs _______ (slowly/rapidly)
  • The nucleation step is rate limiting and energetically _________ (favorable/unfavorable)

back 16

  • ends
  • rapidly
  • unfavorable

front 17

What is critical concentration (Cc)?

back 17

It is the amount of free subunits allowed in the cell

front 18

Fill in the blanks

  • The rate at which subunits add is ________ (proportional/ not proportional) to the concentration of free subunits
  • The rate at which subunits leave is _________(dependent/ independent) to the concentration of free subunits
  • At equilibrium the rates are _______ (equal/not equal)

back 18

  • Proportional
  • independent
  • equal

front 19

When the current concentration is above the Cc there will be net ________ (assembly/disassembly)

back 19

Assembly. They need to use up the subunits so the concentration will lower

front 20

When the current concentration is below the Cc there will be net ________ (assembly/disassembly)

back 20

Disassembly. They need more free subunits to increase the concentration

front 21

T/F Microtubules and microfilaments have the same assembly rates at both ends

back 21

False. It grows faster at the plus end and slower at the minus end (probably because it is already in the right shape to attach. The minus end needs to mold its way in into that shape)

front 22

T/F The plus and minus ends are structurally distinct

back 22

True. The plus end has the indented arrow shape for subunits to easily attach. The minus end is the outwards arrow shape which doesn't match with the subunit's straight edge

front 23

Multiple protofilaments with lateral bonds provide stability

back 23

True. Single ones are unstable (for reasons I don't quite get yet)

front 24

T/F Microtubule assembly is a heterodimer

back 24

True. Alpha and beta subunits stick together and to each other to make long strands. Then the strands are wrapped around in a tube like shape

front 25

T/F Microtubules are stabilized

back 25

True. There are multiple lateral and longitudinal bonds holding them together

front 26

T/F Microfilaments are subunits for the protein actin

back 26

True. Actin is made up of microfilaments

front 27

Search up Nucleotide Hydrolysis in microtubule assembly. Dynamic instability and treadmilling

back 27

Go do it!

front 28

T/F Intermediate filament assembly is not accompanied by nucleotide hydrolysis and they do not have intrinsic polarity

back 28

True. They are not and do not