Rec reading Mol Cell Bio Chapter 16 The Cytoskeleton

Question 1

There are three types of cytoskeletal filaments

Answer 1

Intermediate filaments: mechanical strength

Microtubules: organelles and intracellular transport

Actin: cell shape and movement

Question 2

Accessory proteins

Answer 2

Control the assembly of the cytoskeleton

e.g. molecular motots

Question 3

Cytoskeletal systems are

Answer 3

Dynamic and adaptable - ant trails not highways

Question 4

Microtubules

Answer 4

• Star like array in interphase cell
• Quickly rearrange to form bipolar mitotic spindle
• Also form cilia and flagella
• Also form bundles for transport
• In plant cells, organised arrays of MT direct the pattern of cell wall synthesis

Question 5

Actin

Answer 5

• Underly the plasma membrane in all animal cells
• Provide strength and shape to the lipid bilayer
• Form cell surface projections - lamellipodia and filopodia to sense environment
• Contractile ring during cell division
• Muscle contraction
• Stereocilia in the inner ear tilt in response to sound
• Microvilli on intestinal cells increase apical cell SA

Question 6

Intermediate filaments

Answer 6

• Line inner face of nuclear envelope to form protective cage for DNA: nuclear lamina
• Cytosol form twisted cables to hold epithelial sheets together
• Axon formation in nerve cells
• Hair and fingernails

Question 7

Cells use the cytoskeleton to

Answer 7

Maintain polarity

Between the apical surface and the basolateral membrane

Question 8

The cytoskeleton is integral in differentiation by allowing asymmetric cell division - example

Answer 8

S. cerevisiae - budding yeast
Budding of daughter cell needs polar actin cytoskeleton
Actin cables and actin patches allow high polarity
Actin patches become highly concentrated in growing bud tip
Actin cables align and point towards buds to allow secretion of a new cell wall and direct materials to the site of budding
Overall polarized actin structures influence the orientation of the mitotic spindle

Question 9

Why are cytoskeletal filaments made up of small subunits?

Answer 9

Allows rapid structural reorganisations

Smaller components are able to diffuse in the cytoplasm

Question 10

What type of bonds form between cytoskeletal polymers?

Answer 10

Weak non covalent interactions

Allows rapid assembly and dissasembly

Question 11

What allows the cytoskeleton to be dynamic?

Answer 11

Small subunits

Weak non covalent interactions

Question 12

What do accessory proteins do?

Answer 12

• convert signals into cytoskeletal action
• determine sites of assembly of filaments
• regulate construction of filaments
• change kinetics of filament assembly and disassembly
• harness energy to generate force and growth
• link filaments to organelles or the plasma membrane
• allow movement

Question 13

Why are actin and tubulin highly conserved in eukaryotes?

Answer 13

The filaments interact with so many proteins that structure variability is not possible

Mutations in the shape of the filament might be beneficial for one protein but not for another

So proteins are varied instead