Cytoskeleton

Question 1

What are actin filaments composed of?

Answer 1

Polymer of actin monomers, 7nm in diameter

Actin filaments are globular proteins arranged in a helix found in all eukaryotic cells.

Question 2

What is the diameter of intermediate filaments?

Answer 2

8-12nm in diameter

Intermediate filaments serve as structural proteins in eukaryotic cells.

Question 3

What is the primary role of microtubules?

Answer 3

Cell structure, organization, mitosis, and movement

Microtubules are filaments of tubulin monomers, 25nm in diameter.

Question 4

What is the organization of actin in cells?

Answer 4

Organized in bundles and may form meshed networks

Actin defines the shape of cells and cellular substructures.

Question 5

What are stress fibers?

Answer 5

Contractile actin-myosin bundles in the cytoplasm

Stress fibers play a role in cell movement and shape.

Question 6

What are filopodia?

Answer 6

Finger-like protrusions with loose bundles of actin

Filopodia ensure the cell is moving in the right direction.

Question 7

How abundant is actin in eukaryotic cells?

Answer 7

15 percent of total protein, with 10 percent being actin-binding proteins

Actin is the most abundant protein in eukaryotic cells.

Question 8

What is the structure of G-actin?

Answer 8

Globular protein with hydrophilic R groups on the outside

G-actin binds ATP/ADP and has a pointed end (minus) and a barbed end (plus).

Question 9

What is actin treadmilling?

Answer 9

Monomers added at both ends, faster at the barbed end

Actin appears to have a trail due to this dynamic polymerization.

Question 10

What do actin-binding proteins regulate?

Answer 10

Microfilament dynamics such as severing, annealing, and branching

Approximately 60 actin-binding proteins are involved in this regulation.

Question 11

What role do intermediate filaments play in cells?

Answer 11

Provide stability and cohesion against stretch

They include keratin, vimentin, and neurofilaments.

Question 12

What are keratin monomers?

Answer 12

Fibrous proteins that mesh in the cytoplasm

Keratin allows cells to adhere to the basement membrane and each other.

Question 13

What mutations can cause epidermolysis bullosa?

Answer 13

Mutations in intermediate filaments such as keratin

This condition affects the integrity of skin and mucous membranes.

Question 14

What is the composition of microtubules?

Answer 14

Heterodimers of alpha and beta tubulin

This composition generates polarity with beta tubulin as the plus end.

Question 15

Where do microtubules originate?

Answer 15

In the centrosome (microtubule organizing center, MTOC)

The centrosome duplicates during mitosis.

Question 16

What are microtubule-associated proteins (MAPs)?

Answer 16

Proteins that stabilize microtubules and regulate their dynamics

MAPs are crucial for maintaining microtubule structure.

Question 17

What is the role of kinesins and dyneins?

Answer 17

Kinesins carry cargo from minus to plus end; dyneins move cargo from plus end to minus end

These motor proteins use energy from ATP hydrolysis to transport cargo.

Question 18

True or False: Microtubules are responsible for transport within the cell.

Answer 18

True

They transport cargo along the cell and are components of cilia.

Question 19

What happens to tau protein in Alzheimer’s disease?

Answer 19

It mutates and becomes hyperphosphorylated, leading to neuronal tangles

These tangles are associated with neuronal death.