Bio1U7. Quiz 7

Which statement best describes the cytoskeleton in eukaryotic cells?

• A soft, unstructured gel that fills the cell

• A network of protein filaments that supports cell shape, positions organelles, provides transport tracks, and can enable movement

• A rigid cell wall made entirely of carbohydrates

• A single type of filament that functions only during cell division

Of the three cytoskeletal filament types, which is the narrowest and what is its approximate diameter?

• Microtubules; about 25 nm

• Intermediate filaments; about 10 nm

• Microfilaments (actin filaments); about 7 nm

• Actomyosin filaments; about 15 nm

Actin filaments are composed of linked monomers of actin arranged in a structure that resembles which of the following?

• Triple helix

• Double helix

• Beta sheet

• Coiled-coil dimer

Which cellular function most directly depends on actin–myosin interaction described in the material?

• DNA replication

• Muscle contraction via overlapping actin and myosin filaments in sarcomeres

• ATP synthesis in mitochondria

• Microtubule nucleation at centrosomes

Which cytoskeletal element is described as having multiple strands of fibrous proteins wound together and an average diameter of 8 to 10 nm?

• Actin filaments

• Intermediate filaments

• Microtubules

• Collagen fibers

Which protein forms a type of intermediate filament found in hair, nails, and skin?

• Tubulin

• Myosin

• Keratin

• Dynein

Compared with actin filaments, what is a key functional difference of intermediate filaments?

• They assemble and disassemble more quickly to drive cell motility

• They are specialized to bear tension and maintain cell shape

• They form the smallest cytoskeletal fibers

• They are primarily composed of tubulin dimers

Despite the term "micro" in their name, which cytoskeletal fibers are the largest among actin filaments, intermediate filaments, and microtubes, with a diameter of about 25 nm, and what are they made of?

• Actin filaments; actin monomers

• Intermediate filaments; keratin

• Microtubules; tubulin proteins

• Microtubules; keratin

Which statement correctly describes the basic structure of a microtubule?

• A solid rod composed of actin monomers

• A hollow tube assembled from dimers of α-tubulin and β-tubulin

• A double helix of intermediate filament proteins

• A membrane-bound cylinder of phospholipids

Microtubules are described as dynamic structures. What feature best explains this description?

• They permanently maintain a fixed length

• They can grow and shrink rapidly by adding or removing tubulin proteins

• They only assemble once during embryonic development

• They are resistant to all forms of cellular remodeling