The cytoskeleton

Question 1

What are the three main types of cytoskeletal elements?

Answer 1

• Intermediate filaments
• Microtubules
• Actin filaments

Question 2

What is the primary role of the cytoskeleton?

Answer 2

The cytoskeleton provides structural support, defines cell shape, and facilitates cell movement and division.

Question 3

Describe the structure and function of actin filaments.

Answer 3

• Structure:
  
  • Diameter: ~7 nm
  • Composed of G-actin (monomer) and F-actin (polymer)
  • Polarity with a fast-growing plus end and a slower-growing minus end
• Function:
  
  • Cell movement (e.g., lamellipodia and filopodia)
  • Supports microvilli in epithelial cells
  • Forms contractile structures during cytokinesis

Question 4

What is the role of transmembrane proteins (integrins) in cell adhesion?

Answer 4

Integrins bind to proteins in the extracellular matrix and to actin filaments inside the cell, providing anchorage and facilitating cell movement.

Question 5

Explain the process of actin treadmilling.

Answer 5

• Occurs when there is a high concentration of free actin.
• Monomers add to the plus end faster than ATP is hydrolyzed to ADP, allowing for filament growth.
• At the minus end, ADP is hydrolyzed faster than monomers can be added, leading to shrinkage.

Question 6

What defines dynamic instability in microtubules?

Answer 6

Microtubules exhibit dynamic instability by constantly growing (polymerization) and shrinking (depolymerization), allowing rapid remodeling.

Question 7

What is the structure of microtubules?

Answer 7

• Diameter: ~24 nm
• Composed of α-tubulin and β-tubulin dimers
• Form hollow tubes with structurally distinct ends (plus and minus ends)

Question 8

Describe the function of microtubule motor proteins.

Answer 8

• Kinesins: Move toward the plus end (periphery of the cell)
• Dyneins: Move toward the minus end (center of the cell)
• They transport organelles, vesicles, and macromolecules along microtubules using ATP as an energy source.

Question 9

What are intermediate filaments, and what is their primary function?

Answer 9

• Structure: Diameter of ~10 nm, made of various proteins like keratins and vimentin.
• Function: Provide tensile strength and mechanical stability to cells, especially in tissues subject to stress.

Question 10

How do actin filaments contribute to cell migration?

Answer 10

Actin filaments form protrusions (like lamellipodia) that adhere to surfaces, allowing the cell to drag itself forward through contraction at the rear.

Question 11

What is the significance of the centrosome in microtubule organization?

Answer 11

The centrosome serves as the nucleation site for microtubule growth, anchoring the minus end of microtubules and allowing growth at the plus end.

Question 12

What are the roles of actin-binding proteins?

Answer 12

• Monomer-sequestering proteins: Prevent monomers from binding to filaments.
• Nucleating proteins: Promote actin polymerization.
• Bundling proteins: Hold actin filaments together in bundles.

Question 13

What happens to microtubules when GTP is hydrolyzed to GDP?

Answer 13

The dimers with GDP bind less tightly, leading to a shift towards disassembly and causing the microtubule to shrink.

Question 14

What is the role of nuclear intermediate filaments?

Answer 14

Nuclear lamins form a meshwork that strengthens the inner nuclear membrane and disassembles and reassembles during cell division.

Question 15

What genetic disorder is associated with mutations in keratin?

Answer 15

Epidermolysis bullosa simplex, which leads to increased susceptibility to mechanical injury in the skin.