11Cytoskeleton and Cell Motility (1)

Becker, W.M., et al. (2006). The World of the Cell. 6th Edition. California: Pearson Benjamin Cummings. Chapter 15 & 16
Karp, G. (2008). Cell and Molecular Biology. 5th Edition. New York: John Wiley & Sons. Chapter 9

Upon completing this lecture, you are expected to be able to:

Define the term cytoskeleton.
Explain the properties of the major components of the cytoskeleton.
Describe the major functions of the cytoskeleton.
Identify how certain compounds such as taxol can affect microtubules leading to cell damage.
Describe what motor proteins are and how they are powered.
Contrast the movements of a flagellum and a cilium.

Vertebrate skeleton is a familiar organ system providing support and mediating movements.
Eukaryotic cells possess a ‘skeletal system’ known as the cytoskeleton that serves similar functions.

Comprised of 3 filamentous structures forming an intricate network that supports the cell and facilitates movements.
Each filament is a polymer of protein subunits connected by weak, non-covalent bonds, allowing rapid assembly/disassembly through cellular regulation.
Each cytoskeletal component has distinct mechanical properties.

Microtubules (MTs)
- Hollow, rigid tubes composed of tubulin subunits.
Microfilaments (MFs)
- Thinner, solid structures comprised of actin.
Intermediate Filaments (IFs)
- Tough, ropelike fibers made of various proteins (e.g., keratin in skin cells).

Fluorescence microscopy: Utilizes fluorescent compounds to label cytoskeletal proteins, resulting in glowing specimens.
Live cell fluorescence microscopy: Introduces fluorescent cytoskeletal proteins into live cells for visualization.
Computer-enhanced digital microscopy: Increases contrast and clarity in microscopic images.
Electron microscopy: Resolves individual filaments in detail, revealing structural aspects.

Dynamic Scaffold
- Provides structural support influencing cell shape and resistance to deformation.
Internal Framework
- Positions organelles within the cell, maintaining an organized structure.
Network for Material Movement
- Directs transport of organelles and materials within the cell, including mRNA and vesicles.
Force-Generating Apparatus
- Enables cell movement via cilia, flagella, or pseudopodia. Single-celled organisms can propel through environments, while multicellular organisms move various specialized cells.
mRNA Anchoring Sites
- Facilitate translation process into polypeptides.
Chromosome Separation
- Critical during mitosis and meiosis, acting as an essential component of cellular division.

Property/Filament	Microtubules	Microfilaments	Intermediate Filaments
Structure	Hollow tubes	Intertwined chains	Ropelike fibers
Diameter	25 nm	8-12 nm	8-12 nm
Polarity	Yes	Yes	No
Major Functions	Support, transport	Motility, contractility	Structural support

Structure and Composition: Hollow tubes made of tubulin subunits (13 protofilaments).
Microtubule-Associated Proteins (MAPs): stabilize, organize, and affect rigidity/assembly of microtubules.

Convert ATP into mechanical energy to facilitate movement along microtubules, transporting cellular cargo (e.g., mitochondria, lysosomes).
Types: Kinesins, Dyneins, and Myosins.
- Kinesins: Move towards + end; facilitate anterograde transport.
- Dyneins: Move towards - end; involved in various cellular movements and chromosomal transport.

Common motile appendages with structural similarities but different in motion: cilia are shorter, more numerous; flagella are longer, fewer.
Axoneme Layout: 9+2 arrangement of microtubules.
Dynein Arms: Provide ATP-powered movement.

Structure: Composed of a heterogeneous group with a basic tetramer unit.
Role: Provide tensile strength, support neuron structure, and play a role in skin protection (keratin).