Cytoskeleton I

Question 1

Order the 3 kinds of cytoskeletons in order of increasing diameter

Answer 1

actin filament to intermediate filament to microtuble filament

Question 2

What kind of bonding holds cytoskeletons together?

Answer 2

Non-covalent, to allow for cell movement and its dynamic abilities.

Question 3

Where is intermediate filament located?

Answer 3

Surrounds nucleus and extends to cell periphery to allow for cell to cell communication/cell to ecm communication.

Question 4

Which of the 3 cytoskeletons is the most stable?

Answer 4

Intermediate filament

Question 5

What’s main job of intermediate filament?

Answer 5

Stress absorber. Helps maintain cell structure. Dynamic, and controlled by atp. Also good for signaling and controlling gene regulation networks

Question 6

Are there motors on intermediate filament? Give example of intermediate filament?

Answer 6

1. No.

2. Keratin, used for cell migration and signal activating.

Question 7

What happens if you screw with keratin?

Answer 7

Skin disease

Question 8

Describe intermediate filament structure

Answer 8

Coiled-coil of 2 alpha helices wound. Coiled regions = interrupts by linker domains. Two of these coiled coils bake a tetramer. The tetramer assembles anti para to make it entirely non polar in terms of N and C termini (not talking about charge). Since both ends look alike, no directional movement.

Question 9

Describe actin filament structure

Answer 9

It is made of actin helices, polymerized with ATP. (+) end is still preferred direction of growth.

Question 10

Describe microtubule structure

Answer 10

The monomer consists of an Alpha-beta unit (so the end structure is polar just like actin, and shares the same propensity for (+) direction expansion). One strand of these = tubulin protofilament. You need 13 of these to make the full microtubule. Operates on GTP hydrolysis. Microtubule is a hollow structure.

Question 11

What is the name of the ration which occurs while making microtubule/actin filaments?

Answer 11

Condensation polymerization reaction.

Question 12

What is the point of the ATP/GTP cap?

Answer 12

Purely for stabilization. The ATP/GTP hydrolyzed does nothing to promote the it’s progression, in terms of being utilized as an energy source.

Question 13

What happens when hydrolysis outpaces the filament cap on the (+) end? Which of the 3 filament types are most subjected to this?

Answer 13

1. A catastrophe is likely, in which the filament falls apart until rescued but the appropriate cap component (ATP or GTP)
2. Microtubile filaments

Question 14

Describe nucleation (elongation) process involved in microtubules and actin filaments. What is the rate limiting step?

Answer 14

1. Start with 3 monomers, GTP/ATP at the caps of each. Hydrolyze on both ends and continue to assemble the monomers. (+) end will elongate faster. The reason for this is that hydrolysis on the positive end occurs MORE SLOWLY, allowing for the buildup of the ATP (trinucleotide cap term comes from this). The revers is the case on the (-) end. Hydrolysis occurs too FAST, so you do not get a buildup and the growth continues further on the (+) end
2. Nucleation

Question 15

Where are microtubules found? Describe that structure.

Answer 15

1. Cilia

2. 9 + 2

Question 16

What is a primary cilium?

Answer 16

Only one present per cell, it is important for the signaling pathways. There is no +2 center like in cilia.

Question 17

What is the centrosome? Describe it.

Answer 17

1. Microtubule organizing center
2. Located around a pair of centrioles, and the centrosome center is a gamma-tubulin ring complex which nucleates the (-) ends of the microtubules so that growth in the centrosome only occurs in the (+) end. Note that centriole are in the centrosome and that expansion of the microtubules is still towards the cell periphery.

Question 18

What are microtubule associated proteins (MAPS)

Answer 18

They stabilize either end of the microtuble, ((-) in the case of the y-tubulin)

Question 19

What is Tau?

Answer 19

Tau is a microtubule associated filament. Too much Tau accumulated in neurofibrillary tangles is associated with Alzheimer’s disease.

Question 20

Could you please detail the use of actin filaments?

Answer 20

Actin filaments are responsible for cell movement. They are found in the cell’s cortex and in large amounts.

Question 21

Name some of the toxins involved with actin and microtubules

Answer 21

1. Phallodin: binds and stabilizes actin filament. Found in Death angel mushroom (amanita phalloides)
2. Colchicine: depolymerizes microtubules, comes from autumn crocus.
3. Taxol: found in pacific rew tree. Messes with microtubules by binding to it.

Question 22

What is chemotaxis?

Answer 22

Cell movement. Works by having actin filaments elongate at the (+) side and myosin-II contractions working on the tail end of the cell.

Question 23

Name some ways to increase actin (NOT ACTION) potential.

Answer 23

1. Nucleate more actin filaments.
2. Cut existing actin filaments to make more (+) ends
3. Form branches off of the existing filaments.

Question 24

Describe use of Arp 2/3 and WASP/Scar

Answer 24

Arp 2/3 works by nucleating the sides of actin filaments in order to create for forward potential. Rho signaling triggers it. Arp 2/3 activated by WASP/Scar protein complex

Question 25

What are some of the usages for actin filaments?

Answer 25

Tissue healing
Cell movement
Clathrin dependent endocytosis

Question 26

Describe Lysteria monocytogens

Answer 26

Bacteria which infects cells. It has a protein at its end that is analogous to WASP/Scar protein, enabling it to activate Arp 2/3 at will. The bacteria capitalizes on this by using it to propel through the cytoplasm and travel to different cells. Leads to food poisoning and death.