4.5 The Cytoskeleton
3 min read•june 14, 2024
The cytoskeleton is the cell's dynamic scaffolding system. It's made up of protein filaments that maintain cell shape, enable movement, and facilitate internal transport. This network is crucial for cell division, ensuring genetic material is evenly distributed to daughter cells.
There are three main types of cytoskeletal filaments: , , and . Each type has unique properties and functions, working together to support cellular processes and maintain structural integrity.
Structure and Function of the Cytoskeleton
Structure and function of cytoskeleton
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- Dynamic network of protein filaments extending throughout eukaryotic cell cytoplasm
- Maintains cell shape by providing mechanical support (skeleton of the cell)
- Enables intracellular transport by serving as tracks for organelle and vesicle movement (highways within the cell)
- Crucial for cell division by forming the to segregate chromosomes (ensures genetic material is evenly distributed to daughter cells)
- Consists of three main protein filament types
- ()
- Intermediate filaments
Types of cytoskeletal filaments
- Microfilaments ( filaments)
- Thin, flexible filaments (6-8 nm diameter) composed of monomers
- Enable cell movement (muscle contraction), maintain cell shape
- Support plasma membrane, form cellular protrusions (, )
- Contribute to , which provide tension and support cell adhesion
- Intermediate filaments
- 8-12 nm diameter filaments made of , ,
- Provide mechanical strength, resistance to shear stress (help cells withstand external forces)
- Maintain cell shape, anchor organelles within cytoplasm
- Involved in cell-cell and cell-matrix adhesion (, )
- Microtubules
- Hollow, cylindrical structures (25 nm diameter) of α- and dimers
- Organize cytoplasm, provide tracks for intracellular transport ( and motor proteins move along microtubules)
- Form during cell division to segregate chromosomes
- Provide structural support for and
- Originate from the , which acts as the main microtubule-organizing center
Cellular Motility and Cytoskeletal Differences
Cilia and flagella in motility
- Specialized organelles protruding from cell surface enabling movement
- Structure
- Core of nine doublet microtubules in 9+2 pattern (nine outer doublets around two central singlets)
- Dynein arms connect outer doublets, generate force for movement (ATP-powered motor proteins)
- anchors cilium/flagellum to cell, organizes microtubule assembly
- Function
- shorter, more numerous, beat coordinately to move fluids/particles (respiratory tract, fallopian tubes)
- Flagella longer, less numerous, propel cells through liquid (sperm cells)
Cytoskeleton in prokaryotes vs eukaryotes
- Prokaryotic cells
- Lack true cytoskeleton, possess actin () and tubulin () homologs
- MreB forms helical filament beneath cell membrane, maintains shape, involved in cell wall synthesis
- FtsZ forms at division site, guides cell wall synthesis during binary fission
- Eukaryotic cells
- Complex cytoskeleton with microfilaments, intermediate filaments, microtubules
- Animal cells
- Lack cell wall, rely on cytoskeleton for support and shape
- Intermediate filaments provide tensile strength, resist mechanical stress (skin cells, muscle cells)
- Plant cells
- Cell wall provides support and determines shape
- Microtubules crucial for cell wall deposition during growth and division
- Intermediate filaments less abundant and diverse than in animal cells
Cytoskeleton Dynamics and Cell Polarity
- Cytoskeleton undergoes constant remodeling () to respond to cellular needs
- established and maintained through asymmetric organization of cytoskeletal elements
- connect the cytoskeleton to the extracellular matrix, facilitating cell-substrate interactions
Key Terms to Review (36)
Actin: Actin is a globular multi-functional protein that forms microfilaments. It plays a critical role in muscle contraction by interacting with myosin to produce force and movement.
Actin: Actin is a globular protein that forms microfilaments and plays a crucial role in various cellular functions, including muscle contraction, cell movement, and maintaining cell shape. This protein is a major component of the cytoskeleton, providing structural support to cells and enabling processes such as locomotion and contraction in muscle fibers.
Actin filaments: Actin filaments, also known as microfilaments, are thin, thread-like protein structures that are a key component of the cytoskeleton in eukaryotic cells. They play a crucial role in maintaining cell shape, enabling cell movement, and facilitating intracellular transport. By forming networks and interacting with other proteins, actin filaments are essential for various cellular activities, including muscle contraction and cell division.
Axoneme: An axoneme is the core structure of cilia and flagella, composed of microtubules arranged in a specific pattern that provides the ability to move. This structure is crucial for cellular movement and plays a key role in various biological processes, including locomotion and signaling. The axoneme typically consists of a '9+2' arrangement of microtubules, which refers to nine outer doublet microtubules surrounding two central single microtubules.
Basal Body: A basal body is a cylindrical structure found at the base of cilia and flagella, acting as an anchor for these organelles. It is essentially a modified centriole, playing a crucial role in the assembly and maintenance of cilia and flagella, which are essential for cell movement and signaling. The basal body helps organize the microtubules that make up these structures, ensuring they function effectively in cellular processes.
Caecilians: Caecilians are a group of limbless, serpentine amphibians primarily found in tropical regions. They are adapted to a burrowing lifestyle with elongated bodies and reduced or absent eyes.
Cell polarity: Cell polarity refers to the spatial differences in the shape, structure, and function of cells, which is crucial for their role in tissues and organs. This concept is essential for understanding how cells organize themselves into distinct regions, allowing for specialized functions such as cell signaling, transport, and communication. Cell polarity is tightly linked to the cytoskeleton, as it helps establish and maintain the structural framework necessary for these differences.
Centrosome: The centrosome is a cellular structure that serves as the main microtubule organizing center in eukaryotic cells, playing a crucial role in maintaining cell shape and facilitating cell division. It is typically composed of two centrioles arranged at right angles to each other, surrounded by a protein-rich matrix called the pericentriolar material. The centrosome's functions are vital during the cell cycle, particularly in organizing the mitotic spindle during mitosis.
Cilia: Cilia are hair-like structures that extend from the surface of many eukaryotic cells. They play crucial roles in movement and sensory functions.
Cilia: Cilia are hair-like structures that extend from the surface of many eukaryotic cells and play crucial roles in movement and sensory functions. These tiny organelles are made up of microtubules arranged in a specific pattern and are anchored to the cell by a basal body. Cilia can be found in various organisms, including protists, where they assist in locomotion and feeding, and in multicellular organisms, where they help move fluids across cell surfaces and participate in excretion processes.
Cytoskeleton dynamics: Cytoskeleton dynamics refers to the continuous and regulated changes in the structure and organization of the cytoskeleton, which is a network of protein filaments and tubules that provides shape, support, and movement to cells. This dynamic behavior is crucial for various cellular processes such as cell division, motility, and intracellular transport. The ability of the cytoskeleton to rapidly reorganize allows cells to respond to environmental cues and maintain their functionality.
Desmosomes: Desmosomes are specialized intercellular junctions that provide strong adhesion between cells, particularly in tissues subjected to mechanical stress. They are composed of cadherin proteins and anchor to intermediate filaments within the cell.
Desmosomes: Desmosomes are specialized cell structures that provide strong adhesion between adjacent cells, ensuring the integrity and stability of tissues under mechanical stress. They consist of protein complexes that anchor the cytoskeleton of one cell to that of another, forming a resilient connection that is crucial in tissues like the skin and heart, where cells experience significant tension and strain.
Dynein: Dynein is a motor protein that plays a crucial role in the movement of cellular components along microtubules, which are part of the cytoskeleton. It is responsible for retrograde transport, moving cargo towards the cell body in neurons and facilitating processes such as vesicle transport, organelle positioning, and mitosis. Dynein works in conjunction with other motor proteins like kinesin, and its activity is essential for maintaining cellular organization and function.
Flagella: Flagella are long, whip-like structures that protrude from the surface of certain cells, primarily used for movement. These appendages are essential for many organisms, providing them with the ability to swim through liquids, and they play a crucial role in the biology of various protists and algae.
Focal Adhesions: Focal adhesions are specialized structures that connect a cell's cytoskeleton to the extracellular matrix (ECM), facilitating communication between the inside of the cell and its external environment. These dynamic sites are crucial for processes such as cell migration, signaling, and mechanotransduction, allowing cells to sense and respond to mechanical cues from their surroundings.
FtsZ: FtsZ is a protein that plays a crucial role in bacterial cell division by forming a contractile ring at the future site of cell division. This ring is essential for the process of cytokinesis, which allows bacteria to separate into two daughter cells after replication. FtsZ is homologous to tubulin, a key component of the eukaryotic cytoskeleton, and its behavior offers insights into the evolutionary origins of cellular division mechanisms.
Hemidesmosomes: Hemidesmosomes are specialized structures that anchor epithelial cells to the underlying basement membrane, ensuring cell stability and integrity. They play a crucial role in connecting the cytoskeleton of epithelial cells to extracellular matrix components, facilitating communication between the cell and its environment.
Intermediate filaments: Intermediate filaments are a type of cytoskeletal component found in eukaryotic cells that provide structural support and mechanical strength. They are thicker than microfilaments but thinner than microtubules, playing a crucial role in maintaining cell shape and integrity, as well as anchoring organelles. These filaments connect various cellular components, contributing to cell-cell and cell-matrix connections, which are essential for overall cellular function.
Keratins: Keratins are a family of fibrous structural proteins that are key components of the cytoskeleton in epithelial cells, providing strength and resilience to tissues. These proteins play a vital role in the formation of intermediate filaments, which contribute to cell integrity and protect cells from mechanical stress. Keratins are essential for the structural integrity of skin, hair, nails, and other epithelial tissues.
Kinesin: Kinesin is a type of motor protein that plays a critical role in cellular transport by moving along microtubules within the cytoskeleton. It is essential for transporting cellular cargo, such as organelles and vesicles, towards the plus end of microtubules, facilitating processes like cell division and intracellular signaling. This energy-dependent movement is powered by ATP hydrolysis, making kinesin crucial for maintaining cellular organization and function.
Lamellipodia: Lamellipodia are thin, sheet-like extensions of the cell membrane that play a crucial role in cell movement and migration. These structures are formed by the dynamic polymerization of actin filaments, which are part of the cytoskeleton, allowing cells to push out their membrane and move in response to various signals. Lamellipodia are essential for processes such as wound healing, immune responses, and development.
Lamins: Lamins are a type of intermediate filament proteins that form a dense fibrillar network inside the nucleus of eukaryotic cells, providing structural support and playing crucial roles in nuclear organization and stability. They connect the nuclear envelope to chromatin and other nuclear components, influencing essential processes such as DNA replication and cell division.
Microfilaments: Microfilaments are thin, thread-like protein structures that form part of the cytoskeleton. They are primarily composed of actin and play key roles in cell movement, shape, and division.
Microfilaments: Microfilaments are thin, thread-like structures made primarily of actin protein, forming part of the cytoskeleton in eukaryotic cells. They play crucial roles in cell shape, movement, and division, and are involved in various cellular processes like muscle contraction and cell motility. Microfilaments interact with other components of the cytoskeleton to maintain cellular integrity and facilitate intracellular transport.
Microtubules: Microtubules are cylindrical structures composed of tubulin proteins that form part of the cytoskeleton. They play crucial roles in maintaining cell shape, enabling intracellular transport, and facilitating cell division.
Microtubules: Microtubules are cylindrical structures composed of tubulin protein subunits, playing essential roles in maintaining cell shape, facilitating intracellular transport, and organizing the mitotic spindle during cell division. These dynamic components of the cytoskeleton are crucial for various cellular functions, contributing to the overall organization and movement within eukaryotic cells.
Microvilli: Microvilli are tiny, finger-like projections that extend from the surface of epithelial cells, primarily in the intestines and kidneys. They serve to increase the surface area of these cells, enhancing their ability to absorb nutrients and other substances. This structural adaptation is crucial for efficient nutrient uptake and plays a role in various biological processes.
Mitotic spindle: The mitotic spindle is a structure composed of microtubules that segregates chromosomes into daughter cells during mitosis. It ensures accurate chromosome alignment and separation to facilitate cell division.
Mitotic spindle: The mitotic spindle is a structure formed by microtubules that organizes and separates chromosomes during cell division. This essential apparatus ensures that each daughter cell receives an accurate and equal distribution of genetic material, facilitating the orderly process of mitosis and maintaining genetic integrity in eukaryotic cells.
MreB: MreB is a protein that plays a crucial role in maintaining the shape and structure of bacterial cells, particularly rod-shaped bacteria. It is an actin-like protein that forms a dynamic cytoskeletal network beneath the cell membrane, helping to coordinate cell growth and division. MreB is essential for determining the cell's morphology by directing the placement of cell wall synthesis machinery.
Stress Fibers: Stress fibers are contractile bundles of actin filaments found in non-muscle cells that play a critical role in maintaining cell shape, adhesion, and motility. They are part of the cytoskeletal system and help to generate tension within the cell, which is essential for processes such as cell division and wound healing.
Vimentins: Vimentins are a type of intermediate filament protein found in the cytoskeleton of mesenchymal cells, providing structural support and resilience. They play a crucial role in maintaining the integrity of the cell shape, participating in cell signaling, and influencing cellular functions like migration and division. Vimentins are essential for tissue repair and are often used as markers in various diseases, particularly those related to epithelial-mesenchymal transition.
Z-ring: The Z-ring is a structure formed during cell division in prokaryotic cells, specifically at the site of cytokinesis. It plays a crucial role in the process of binary fission, where it helps to constrict the cell membrane, leading to the separation of daughter cells. The Z-ring is composed mainly of the protein FtsZ, which is similar to tubulin in eukaryotic cells, and its formation marks the midpoint of a dividing cell.
α-tubulin: α-tubulin is a protein that plays a crucial role in the formation of microtubules, which are structural components of the cytoskeleton in eukaryotic cells. It pairs with β-tubulin to form heterodimers that polymerize into long, hollow tubes, providing mechanical support and facilitating intracellular transport. Microtubules are essential for various cellular processes, including cell division, maintaining cell shape, and enabling motility.
β-tubulin: β-tubulin is a type of tubulin protein that is essential for the formation of microtubules, which are crucial components of the cytoskeleton in eukaryotic cells. It pairs with α-tubulin to form heterodimers, the building blocks of microtubules, playing a vital role in maintaining cell shape, enabling intracellular transport, and facilitating cell division. The dynamic assembly and disassembly of microtubules, driven by β-tubulin's GTP-binding properties, allow cells to respond to various physiological signals.