L22 Cell Motility: Microtubules And Actin Filaments

Question 1

What do cell motility need?

Answer 1

Energy and guidance (direction) and mechanical interaction with something outside the cell

Question 2

What are the two structures that are needed for microtubule- based motility?

Answer 2

Cilia and flagella

Question 3

What are cargoes?

Question 4

What are the cargoes of cells?

Answer 4

Protozoa
Sperm

Question 5

What are the cargoes of fluids?

Answer 5

Respiratory
Reproductive tract

Question 6

Give adaptation of microtubules

Answer 6

Hollow tubule (of alpha and beta tubulin) - rigid structure
Cross section is 24nm in diameter (13 protofilaments)
Alternating alpha and beta tubulin creates a tubulin dimer

Question 7

What are the similarities and differences between cilia and flagella structure?

Answer 7

Similarity:
Same structure

Differences:
Different length
Cilia: 2-10. X 0.25um
Flagella: 100-200 x 0.25um

Question 8

What is the axoneme?

Answer 8

It’s the core structure of cilia and flagella, responsible for their movement

Question 9

What are the key features of an axoneme?

Answer 9

Complete (A) fibres 13 protofilaments
Incomplete (B) fibres 10 protofilaments
- Dynein arms: motor proteins generates sliding motion between microtubule pairs
- Typically a “9+2” structure with 9 pairs of microtubules arranged in a ring around a central pair
Nexin links: Connects adjacent microtubule doublets, limiting slide and coordinating movement (causes a bend)

Question 10

How are the waveforms different for cilia and flagella? (Write which uses inner and outer arm)

Answer 10

Cilia - back and forth pattern, resembling a whip-like motion

Flagella - wave like motion

Question 11

What does Nexin do?

Answer 11

Forms a bridge joining the pairs of A and B microtubules.

Question 12

Describe the structure of basal body

Answer 12

Instead of 9+2 its 9 x 3 microtubule array
0.2 um x 0.4 um (diameter x length)

Cylindrical pattern

Question 13

What is basal body?

Answer 13

It’s a modified centriole, serving as the anchor of the axoneme

Question 14

Where can the motility for the actin- based motility come from?

Answer 14

Motors and turnovers

Question 15

Describe the structure of actin filament structure

Answer 15

Actin filament has polarity - plus and minus end
ATP hydrolysed when filament polymerises

Question 16

Describe the structure of microtubule structure (listen to the guy)

Answer 16

1. Alpha and beta subunit dimers.
2. Nucelotides in both are GTP/GDP.

Question 17

What are tubulin dimers?

Answer 17

Each tubulin dimer consists of an alpha and beta tubulin protein

Question 18

What are protofilaments?

Answer 18

Tubulin dimers polymerise head to tail to form linear chains called protofilaments

Question 19

What is actin treadmilling?

Answer 19

Where monomers are continuously added to one end and removed from the other end of an actin filament

Question 20

Compare the actin filament vs microtubule structure

Answer 20

1. Diameter - 5-9, 24
2. Form - Solid, hollow
3. Subunits - Homomeric, a/b heterodimers
4. Nucleotide in monomer - ATP, GTP.

Question 21

Describe the myosin structure

Answer 21

Head domain: motor domain of myosin
Contains binding sites for actin and ATP

Question 22

What structures do actin need?

Answer 22

• Filopodium - thin, finger - like protrusions that extend from the cell surface
• Lamellipodium - sheet-like protrusions that form at the leading edge of migrating cells
• Stress fibres -
  Cortical actin

Question 23

What does profilin does to monomers?

Answer 23

1. Inhibits nucleation
2. binds to ATP actin

Question 24

What does cofilin do?

Answer 24

Severing action.

Question 25

Processes of Actin-Binding Preoteins?

Answer 25

1. Monomer nucleating
2. Monomer sequestering
3. Capping
4. Monomer polymerization
5. Depolymerizing
6. Bundling
7. Filament severing
8. Membrane Binding

Question 26

What is myosin?

Answer 26

It is the microfilament motor protein for Cytoskeleton or muscle which has actin filament.

Question 27

Describe the structure of Myosin?

Answer 27

1. C-terminus and N-terminus at ends.
2. Coiled with two alpha helices
3. Two light chains at the Nterminus end
4. 150nm long and 2nm wide