Module 8- The Cytoskeleton and Cell Motility

Cytoskeleton

A network of fibers that provides structural support and shape to the cell.

Profilaments

Microtubules arranged in longitudinal rows, forming structures like spindles, centrioles, cilia, and flagella.

MAPs

Microtubule-associated proteins that increase stability by assembling tubulin subunits together; tau is a great example.

Motor proteins

Proteins that generate the force needed to move organelles within the cell.

Kinesins

Tetrameric motor proteins with 2 light and 2 heavy chains that use ATP hydrolysis to move materials outward from the cell along microtubules.

Dynein

Motor proteins that move along microtubules with 2 heavy chains, typically moving in one direction towards the minus end.

Microtubule-organizing centers (MTOCs)

Sites where nucleation occurs, controlling the number of microtubules, their polarity, number of protofilaments, and the timing and location of assembly.

Centrosome

The best-studied MTOC, consisting of two centrioles and serving as a major site for microtubule initiation.

Basal body

A type of MTOC located at the base of cilia and flagella, which can transform into centrioles and vice versa.

Microtubule structure and dynamics

Regulate intracellular transport through the organization and assembly of microtubules.

Directed movement by motor proteins

Kinesins and dyneins generate movement by traveling along microtubules, facilitating the transport of cellular components.

Tubulin

a globular protein that polymerizes to form microtubules, which are essential hollow, cylindrical structures in eukaryotic cell. Dynamic, ATP bound at plus end, stabilized the protein and signals for growth.

Dynamic instability

the coexistence of growing and shrinking microtubule populations within a cell, where individual microtubules randomly switch between slow growth and rapid shortening.

Cilia

Has basal body and continuous with plasma membrane. Hairlike structure, in surface of cells, motile cilia: moves fluid through tracts. Nonmotile: there is 1 per cell, sensory organelle.

Flagella

Basal body and continuous with plasma membrane, comes in single or a pair, generate movement through beating waves, disassembly by: post translational modifications, cold temp, pressure and high levels of calcium.

Axoneme

At the core of cilia and flagella, composed of 9 pairs of microtubules around and 2 in the middle.

Intracellular transport

the directed movement of vesicles, organelles, and molecules (like mRNA) within a cell, vital for maintaining cellular organization, function, and communication. It uses the cytoskeleton as tracks (microtubules or actin filaments) powered by motor proteins (dynein, kinesin, myosin) to transport cargo to specific destinations

Intermediate filaments

Only in animal cells, strong, flexible, rod-like, used for physical stress. There are 5 major classes.

Architecture of IFs

1. Globular terminal (alpha helix) 2. Dimers parallel 3. Anti-parallel dimers (lack polarity) 4. 8 tetramer 5. Elongated IFs.

Actin

(microfilaments) are thin, flexible protein fibers (~7 nm diameter) forming a dynamic cytoskeleton in eukaryotic cells.

Keratin-IFs

Structural protection, epithelial cells, nuclear envelope.

Neurofilaments

intermediate filament proteins forming the primary structural cytoskeleton of neurons, particularly in axons. Axon parallel.

Plectin

cytolinker protein that maintains cellular integrity and mechanical strength by thin-cross bridges, binding site for IFs.

Myosin

A type of motor protein that interacts with actin filaments to produce muscle contraction and movement in cells.

Conventional myosin

A class of myosin that primarily functions in muscle contraction and is characterized by its ability to form thick filaments.

Unconventional myosin

A group of myosins that do not form thick filaments and are involved in various cellular processes such as vesicle transport and cell motility.

Actin-binding proteins

Proteins that bind to actin filaments and regulate their dynamics, stability, and organization within the cell.

Lamellipodium

A sheet-like projection of the plasma membrane that extends from the leading edge of a moving cell, facilitating cell migration.

Structure and function of microtubules

Microtubules are cylindrical structures made of tubulin proteins that provide structural support, facilitate intracellular transport, and play a key role in cell division by forming the mitotic spindle.

Motor proteins: Kinesins and Dyneins

Kinesins are motor proteins that transport cellular cargo toward the plus end of microtubules, while dyneins move cargo toward the minus end, both utilizing ATP for energy.

Microtubule-organizing centers

Microtubule-organizing centers (MTOCs), such as centrosomes, are structures that anchor the minus ends of microtubules and facilitate their growth and organization within the cell.

The structure and function of Cilia and flagella

Cilia and flagella are hair-like structures composed of microtubules arranged in a 9+2 pattern that facilitate movement and fluid flow across cell surfaces, with cilia being shorter and more numerous than flagella.

The organization of intermediate filaments within epithelial cells

Intermediate filaments are cytoskeletal components that provide mechanical strength and structural integrity to epithelial cells, helping to maintain cell shape and resist stress.

Actin and Myosin structure and assembly

Actin is a globular protein that polymerizes to form filaments, while myosin is a motor protein that interacts with actin filaments to facilitate muscle contraction and cellular movement.

The role of actin-binding proteins in the cell

Actin-binding proteins regulate the dynamics of actin filaments by controlling their polymerization, depolymerization, and organization, thus influencing cell shape, motility, and division.

Cellular motility in Listeria monocytogenes

Intracellular pathogen.it uses the host's actin polymerization machinery to propel itself within and between cells, enhancing its motility and ability to spread infection.

Which of the following proteins can move along the actin filaments?

myosin

3 multiple choice options

Which of the following is the site of microtubule initiation at the base of the flagellum?

Basal body

3 multiple choice options

How are cytoskeleton protein subunits held together?

Noncovalent bond

Which of the following would you NOT find in a sample of plant cells?

Intermediate filament

3 multiple choice options

Which of the following controls the assembly and disassembly of intermediate filaments?

phosphorylation/dephosphorylation

3 multiple choice options

A cell product must be transported toward the plus end of the microtubule near the plasma membrane. Which of the following would the cell most likely use?

Kinesin

3 multiple choice options

Which of the following is NOT true of microtubules?

Trimeric building blocks

3 multiple choice options

A mutation in which protein would result in the destabilization and improper assembly of microtubules?

MAPS

3 multiple choice options

What is the direct source of energy that powers kinesin motor proteins?

Hydrolysis of ATP

acterial cytoskeleton has 3 types, what are they?

ParM (separates two sister plasmids), CreS (cell shape), FtsZ (separates 2 daughter cells)