Cell Biology Chapter 17

What structures organize and support the contents of eukaryotic cells?

The cytoskeleton, composed of intermediate filaments, microtubules, and actin filaments.

What is the main role of intermediate filaments?

Provide mechanical strength to cells.

What structure do some intermediate filaments form inside the nucleus?

The nuclear lamina.

How are intermediate filaments connected to other cytoskeletal elements?

Through linker proteins.

What are microtubules made of?

Globular tubulin dimers.

How do microtubules display polarity?

They have a fast-growing plus end and a slow-growing minus end

From where do microtubules typically grow?

Microtubule-organizing centers (MTOCs), like centrosomes.

What is the function of γ-tubulin complexes?

They nucleate microtubule growth and cap minus ends.

What is dynamic instability in microtubules?

Rapid switching between growth and shrinkage.

What promotes microtubule shrinkage?

GTP hydrolysis in tubulin dimers.

Name two motor proteins that move along microtubules.

Kinesin and dynein.

What do kinesins and dyneins transport?

Organelles, vesicles, and other cellular cargo.

What structures contain bundles of stable microtubules and beat rhythmically?

Cilia and flagella.

What causes cilia and flagella to bend?

Dynein-driven sliding of microtubules.

What are actin filaments composed of?

Helical polymers of globular actin monomers.

How does actin filament polarity compare to microtubules?

Both have a plus end (fast-growing) and minus end (slow-growing).

What controls actin assembly and disassembly?

ATP hydrolysis and actin-binding proteins.

What is the cell cortex?

A dense network of actin filaments under the plasma membrane.

What cellular functions involve the cell cortex?

Cell shape, surface movement, and crawling.

How do actin and microtubules work together in cells?

They establish polarity and coordinate migration, division, and development.

What do myosin motor proteins do?

Move along actin filaments using ATP hydrolysis.

What is the difference between myosin I and myosin II?

Myosin I carries cargo along actin; myosin II slides actin filaments past one another.

What are myofibrils?

Repeating arrays of actin and myosin filaments in muscle cells.

What triggers muscle contraction?

A rise in cytosolic Ca²⁺ levels.

Actin-binding protein

Protein that interacts with actin filaments to regulate assembly, stability, and organization.

Actin filament

Helical polymer of actin monomers; part of the cytoskeleton

Cell cortex

Meshwork of actin filaments beneath the plasma membrane.

Centriole

Cylindrical structure in centrosomes helping organize microtubules.

Centrosome

Main microtubule-organizing center of animal cells.

Cilium

Short, hairlike projection used for cell movement or fluid flow.

Cytoskeleton

Network of protein filaments giving cell shape, organization, and movement.

Dynamic instability

Rapid switching between growth and shrinkage of microtubules.

Dynein

Microtubule motor protein moving toward the minus end.

Filopodium

Thin, actin-rich projection from the cell surface.

Intermediate filament

Strong, rope-like cytoskeletal element for mechanical stability.

Keratin filament

Type of intermediate filament found in epithelial cells.

Kinesin

Microtubule motor protein moving toward the plus end.

Lamellipodium

Broad, sheet-like actin structure at the edge of migrating cells.

Microtubule

Hollow tube made of tubulin dimers, part of the cytoskeleton.

Microtubule-associated protein (MAP)

Protein that binds microtubules and affects stability or organization.

Motor protein

Protein that converts chemical energy into movement along filaments.

Myofibril

Repeating units of actin and myosin in muscle cells.

Myosin

Motor protein moving along actin filaments.

Myosin filament

Filament formed by bundled myosin II molecules.

Myosin 1

Myosin carrying cargo along actin tracks.

Myosin 2

Myosin responsible for muscle contraction and actin filament sliding.

Nuclear lamina

Network of intermediate filaments supporting the nuclear envelope.

Polarity

Structural or functional asymmetry in cells or filaments

Rho protein family

GTPases regulating actin cytoskeleton dynamics.

Sarcomere

Contractile unit of muscle cells in myofibrils.

Treadmilling

Phenomenon where actin filaments grow at one end while shrinking at the other.

Tubulin

Protein building block of microtubules.