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BIO 230 > Lecture 2: Cytoskeletal Networks > Flashcards

Lecture 2: Cytoskeletal Networks Flashcards

1
Q

What are examples of the polar cytoskeleton organization in polarised cells

A
  • Polar microtubules can transport vesicles and proteins to different ends of the cell
  • Polarized actin can define cell shape and behaviour
  • Intermediate filaments also contribute to cell polarity
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2
Q

What are the dynamic changes that the cytoskeleton undergoes? (in terms of actin, myosin)

A
  • interphase crawling/migrating cell
    * Microtubules radiate from cell centre.
    * Actin enriched at cell cortex
  • mitosis
     * Microtubules form the mitotic spindle 
  * Actin at cell cortex disassembles
  • cytokinesis
             * Microtubules keep cell component separate
       * Actin forms the contractile ring
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3
Q

How do polar tubulin dimers form polar microtubules

A
  • Monomeric proteins - tubulin & β-tubulin form dimers
  • Tubulins can bind and hydrolyze GTP
  • Tubulin heterodimers assemble head-to-tail to make polarized protofilaments
  • -tubulin is found at the minus-end
  • β-tubulin defines the plus- end
  • 13 protofilements associate to form a hollow microtubule
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4
Q

what associates to form a (hollow) microtubule

A
  • 13 protofilements associate to form a hollow microtubule
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5
Q

Microtubules exist in a state of dynamic instability. explain

A

They can grow and shrink
*There’s rapid growth with the GTP capped end
* there’s random loss of GTP cap
* there will eventually have heterodimers at the end which leads to
* rapid shrinkage
* regain of GTP cap
*rapid growth with GDP cap end

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6
Q

Describe the T and D for heterodimer in microtubules

A

T-form heterodimer - GTP bound , beta-GTP,alpha -GTP

D form heterodimer - GDP bound , beta-GDP, alpha-GTP

alpha- always bound to GTP

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7
Q

How does gamma tubulin help to nucleate microtubules

A

*gamma-tubulin) interacts with -tubulin at the minus-end
* gamma -tubulin nucleates or stabilizes the minus-end
*gamma-tubulin protects microtubules from depolymerization at the minus end
* Plus-ends grow away from the nucleation
site

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8
Q

Where is gamma-tubulin found in ANIMAL cells (connective tissue)

A

near centrioles on the pericentriolar material.
microtubules grow from gamma-tubulin ring complexes on the centrosome

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9
Q

Where is gamma-tubulin found in plant cells

A

In many plant cells gamma-tubulin is found on other microtubules

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10
Q

How are vesicles and organelles transported along microtubules

A

MAPs = microtubule-associated proteins

  • Some KINESINS can “walk” towards the PLUS end
  • Some DYNEINS can move toward the MINUS end
  • Both motors can hold onto vesicles or organelles with their other domain
  • Both motors use ATP hydrolysis for energy
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11
Q

Which of these statements about microtubules is true?
a) When a centrosome is present, each microtubule contains a variable number of protofilaments.

b) Long, growing microtubules will contain GTP and GDP
.
c) A cell with many microtubules will not have any actin filaments.

d) ɣ-tubulin stabilizes microtubule minus ends by anchoring them onto a cylindrical centriole core.

A

B

For a, there are always 13 protefilaments
and for d- they are anchored on the centrosome, not the centriole

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12
Q

How do polar actin monomers form polar actin filaments

A
  • Actin monomers are asymmetric (so they are polar)
  • Actin monomers can bind and hydrolyze ATP
  • Polar actin monomers assemble into polarized actin filaments, usually two strands twisted together
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13
Q

How does ARP2/3 complex help nucleate actin filaments?

A
  • The ARP2/3 complex nucleates the minus end of actin filaments and protects them from depolymerization
  • Plus-ends grow away from the ARP2/3 complex
  • ARP2/3 can nucleate actin filaments on pre-existing filaments
    • The whole network can undergo treadmilling
  • Proteins sever the minus ends to release them from ARP2/3
  • Proteins cap the plus ends to shape the network
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14
Q

How do Actin treadmilling and adhesions help cells crawl

A
  • The growing actin network pushes the cell leading edge forward
  • Actin and myosin contract to bring the lagging edge forward
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15
Q

How do Integrins anchor actin filaments to the extracellular matrix

A
  • Integrins directly bind extracellular matrix proteins
  • Integrins indirectly interact with actin filaments
  • Actin-integrin-extracellular matrix interactions can provide the adhesion necessary for cell migration
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16
Q

How do Actin & myosins can generate contractile forces

A
  • There are many types of myosins
  • Myosins motor domains use ATP hydrolysis for energy
  • Myosins can hold onto vesicles or organelles with their other domain or myosins can help cells contract
  • Some myosins can “walk” towards the plus end of actin filaments
  • Actin and myosin work together to generate force (e.g. cell migration or muscle contraction)
17
Q

A graduate student adds actin monomers and ATP into a test tube with a buffer that resembles the cell cytosol. What else must be added to the tube to produce ADP?
a) Severing protein cofilin.
b) Nucleating protein ARP2/3.
c) Cofilin and ARP2/3.
d) Nothing.

A

D

18
Q

How does Rho family small GTPases can influence actin organization

A
  • Rho family GTPases can act like
    molecular switches
  • Rho family GTPases (Rho, Rac, and Cdc42) can influence actin organization
  • Actin organization affects cell shape, cell polarity, and cell behaviour
19
Q

How does actin organization can influence cell shape & behaviour

A
  • Rac-GTP activation dominates at the leading tip (lamellipodia) to explore and to push the cell forward
  • Rho-GTP activation dominates at the back to pull the back of the cell
20
Q

Which of the following would most directly increase the amount of constitutive protein secretion?

a) A chemical that increases the formation of COPI-coated vesicles.
b) A chemical that increases the formation of COPII-coated vesicles.
c) A chemical that increases the formation of clathrin-coated vesicles.
d) A chemical that increases the activation of ESCRT-0.

A

b

21
Q

How does cytoskeletal organization define cell polarity

A
  • Symmetry breaking defines anterior vs posterior
  • This triggers cytoskeleton polarization in the fertilized egg
  • Actin filaments are organized by a gradient of small GTPase activity
  • Microtubules are organized by centrosomes near where the sperm entered

BIO 230 (5 decks)

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