Chapter 13-Cytoskeletal Systems

What is the cytoskeleton and its primary functions?

The cytoskeleton is a network of interconnected filaments and tubules that provide physical support, enable cell movement, and facilitate cell division.

List the three major structural elements of the cytoskeleton.

Microtubules, microfilaments, and intermediate filaments.

What are microtubules composed of?

Microtubules are composed of tubulin subunits.

What is the diameter of microtubules?

Microtubules are about 25 nm in diameter.

What subunits compose microfilaments?

Microfilaments are composed of actin subunits.

What is the diameter of microfilaments?

Microfilaments are 7 nm wide.

What is the diameter range of intermediate filaments?

Intermediate filaments range from 8 to 12 nm.

What are septins?

Septins are proteins that can form polymer networks within cells.

How do microtubules contribute to muscle contraction?

Microtubules are structural elements of cilia and flagella, aiding in movement.

What is dynamic instability in microtubules?

Dynamic instability refers to the ability of microtubules to rapidly assemble and disassemble in response to changes in tubulin concentration.

What are the two types of microtubules?

Cytoplasmic microtubules and axonemal microtubules.

What roles do cytoplasmic microtubules play in the cell?

Maintaining axons, forming mitotic and meiotic spindles, altering cell shape, and orienting cellulose microfibrils.

What structures do axonemal microtubules stabilize?

Cilia and flagella.

What is the basic structure of microtubules?

Microtubules are straight, hollow cylinders composed of protofilaments.

What is a protofilament?

A protofilament is a linear array of tubulin heterodimers that forms the basic subunit of microtubules.

What are the N-terminal and C-terminal domains in tubulin subunits known for?

The N-terminal domain binds GTP, while the C-terminal domain interacts with microtubule-associated proteins (MAPs).

How is microtubule polarity established?

Microtubule polarity arises from the orientation of tubulin dimers within protofilaments.

What occurs during microtubule nucleation?

Nucleation is the process by which tubulin dimers aggregate into oligomers that serve as seeds for microtubule growth.

What are the phases of microtubule assembly?

Lag phase, elongation phase, and plateau phase.

What is critical concentration in terms of microtubule assembly?

The tubulin concentration at which microtubule assembly is balanced by disassembly.

Which end of the microtubule grows faster, plus or minus?

The plus end grows faster than the minus end.

What is treadmilling in microtubules?

Treadmilling is when tubulin dimers are added at the plus end while being removed from the minus end.

What effect do antimitotic drugs have on microtubules?

Antimitotic drugs prevent microtubule assembly and promote disassembly, affecting cell division.

What is the function of colchicine?

Colchicine binds to β-tubulin and inhibits microtubule assembly.

How does paclitaxel (Taxol) affect microtubules?

Paclitaxel binds tightly to microtubules and stabilizes them, causing depletion of free tubulin subunits.

What is the role of γ-tubulin in the centrosome?

γ-Tubulin forms ring complexes that serve as nucleation sites for microtubule assembly.

What is the structural composition of centrioles?

Centrioles are formed by nine pairs of triplet microtubules.

Describe the function of intermediate filaments.

Intermediate filaments provide mechanical strength and support in cells.

What is keratin and where is it found?

Keratin is an abundant intermediate filament protein found in epithelial cells, hair, and nails.

What are the classes of intermediate filament proteins?

Classes include acidic keratins, basic keratins, vimentin, neurofilament proteins, nuclear lamins, and nestin.

What are plectins and their role concerning intermediate filaments?

Plectins are accessory proteins that stabilize and cross-link intermediate filaments.

What is the primary component of microfilaments?

Actin is the primary component of microfilaments.

How do actin filaments contribute to muscle contraction?

Actin filaments slide past myosin filaments to facilitate muscle contraction.

What defines the cell cortex?

The cell cortex is a layer rich in actin filaments just beneath the plasma membrane.

What is the process of cytoplasmic streaming?

Cytoplasmic streaming is the rapid movement of organelles and components throughout the cell.

Define treadmilling in actin filaments.

Treadmilling occurs when addition of actin monomers at the plus end equals the loss of monomers at the minus end.

How does ATP hydrolysis relate to actin filaments?

ATP hydrolysis to ADP decreases filament stability and promotes disassembly.

What triggers muscle contraction?

A sudden rise in cytosolic Ca2+ triggers muscle contraction.

What is the role of myosin in muscle cells?

Myosin interacts with actin filaments to facilitate muscle contraction.

Describe the sliding filament mechanism of muscle contraction.

During contraction, actin and myosin filaments slide past each other.

What is the significance of sarcomeres?

Sarcomeres are the basic contractile units of muscle cells.

What happens to the nuclear lamina during cell division?

The nuclear lamina disassembles and reforms during cell division.

What role do drugs like cytochalasins play regarding actin filaments?

Cytochalasins cap the plus ends of actin filaments, preventing polymerization.

What is the function of formins and ARPs in relation to actin?

Formins and actin-related proteins (ARPs) promote actin polymerization.

How do extracellular signals influence actin dynamics?

Extracellular signals can trigger changes in actin assembly to alter cell shape and movement.

What characterizes the biomechanical properties of intermediate filaments?

Intermediate filaments provide tensile strength and resistance to mechanical stress.

Explain what happens during the process of muscle relaxation.

Muscle relaxation occurs when cytosolic Ca2+ levels return to baseline, leading to the detachment of myosin from actin.

What is the role of actin binding proteins?

Actin binding proteins modulate the assembly and disassembly of actin filaments.

How do actin filaments ensure cellular motility?

Actin filaments generate forces that allow cells to crawl along surfaces.

Define the role of the centrosome in microtubule organization.

The centrosome serves as the main microtubule-organizing center, anchoring microtubules.

What is myosin-II and its significance in muscle cells?

Myosin-II is the type of myosin that forms filaments and is essential for muscle contraction.

How does the apical actin layer enhance cell surface function?

The apical layer of actin filaments supports structures like microvilli that enhance absorption.

What condition is characterized by mutations in keratin genes?

Epidermolysis bullosa simplex results from mutations in keratin genes, leading to susceptibility to skin injuries.

Describe the function of the nuclear lamina.

The nuclear lamina provides structural support to the nucleus and organizes chromatin.