Cytoskeleton

Question 1

What are the components of cytoskeleton?

Answer 1

• microtubules
• microfilaments
• intermediate filaments

Question 2

What is the structure, dimension and examples of cytoskeleton?

Answer 2

Microtubules = protofilaments, 25nm, tubulin (α and β)
Microfilaments = double helix, 6-7nm, actin
IF = 2 antiparallel helices, 10nm, vimentin/desmin/keratin

Question 3

What is the structure of microtubules?

Answer 3

• polymer of α and β tubulin dimers
• GTP-binding subunits = protofilaments
• add GTP at growing end

Question 4

What is dynamic instability in microtubulues?

Answer 4

• balance btwn polymerization, catastrophe, rescue
• subunit concentration and temperature dependent
• GTP-β- tubulin cap

Question 5

What are 3 regulating proteins of microtubules?

Answer 5

Microtubule Associated Proteins
- alter MT stability – regulate with phosphorylation

+TIPs (+ end tracking proteins)
- stabilize MT to reduce catastrophe (EB1)

MT Severing Proteins
- destabilize MT (Katanin)

Question 6

What are 2 motor proteins?

Answer 6

Kinesin and Dynein

Question 7

What are the properties of kinesin?

Answer 7

(+) end motor protein
heavy chains (ATP activity + bind MTs)
light chains (recognize cargo)
anterograde transport

Question 8

What are the properties of dynein?

Answer 8

(-) end motor protein
ATPase activity
interact with dynactin - binds to cargo
retrograde transport

Question 9

What are the properties of microfilaments?

Answer 9

• G-actin (globular) and F-actin (filamentous)
• grows at + and - ends
• ATP dependent
• Profilin = polymerize and Cofilin = depolymerize

Question 10

What is branched actin?

Answer 10

• adding laterally to existing actin
• using Actin Related Protein 2/3 Complex (Arp 2/3)

Question 11

What is the motor protein of microfilaments?

Answer 11

Myosin
I = membrane association
II = contraction
III = organelle transport

Question 12

What are the cellular structures of actin cytoskeleton?

Answer 12

Bundles (Fimbrin and α-actinin) - microvilli/fillipodia
Networks (Spectrin and Filamin) - inner PM/leading edge
Support Structures (dystrophin) - PM actin linking

Question 13

How does actin work in the sarcomere?

Answer 13

ATP and Calcium added
- A band decreases and Z disks come closer together
- Contraction occurs

Question 14

What is the structure of IF?

Answer 14

Tetramer = 4 polypeptides
Protofilament = 4 tetramers
Protofibril = 4 protofilaments

• no polarity or motor proteins

Question 15

What are the types of IF and where are they found?

Answer 15

I – Acidic Keratins
II – Basic Keratins (epithelial)
III – Desmin (muscle) and Vimentin (mesenchymal)
IV – Neurofilaments (neurons)
V – Lamins (nucleus)

Question 16

What are the properties of IF?

Answer 16

• dynamic (ish)
• segments can be taken out and replaced
• phosphorylation of Ser = disassemble