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Honors Biology
Table of Contents
Unit 3 Overview: Cell Structure and Function
3.1 Cell Theory and Types of Cells
3.2 Eukaryotic Cell Organelles and Their Functions
3.3 Prokaryotic Cell Structure
3.4 Cytoskeleton and Cell Movement

🐇honors biology review

3.4 Cytoskeleton and Cell Movement

Citation:

The cytoskeleton is like your body's internal scaffolding, giving cells shape and allowing them to move. It's made up of three main parts: microfilaments, intermediate filaments, and microtubules. Each plays a unique role in keeping cells sturdy and mobile.

Cells can also have special structures called cilia and flagella that help them move or push stuff around. These tiny appendages work with the cytoskeleton to enable cell movement, which is crucial for everything from wound healing to how cancer spreads.

Cytoskeletal Components

Microfilaments

  • Composed of actin proteins arranged in a double helix structure
  • Measure 7 nm in diameter, making them the thinnest of the cytoskeletal components
  • Provide mechanical support and determine cell shape
  • Enable cell movement through the formation of pseudopodia (temporary cytoplasmic projections)
  • Involved in muscle contraction by interacting with myosin filaments
  • Play a role in cytokinesis during cell division by forming the contractile ring

Intermediate Filaments

  • Consist of various proteins, such as keratin, vimentin, and lamin
  • Measure 8-12 nm in diameter, falling between microfilaments and microtubules in size
  • Provide mechanical strength and resistance to shear stress
  • Help maintain cell shape and anchor organelles within the cytoplasm
  • Found in abundance in cells subjected to mechanical stress (epithelial cells)
  • Form the nuclear lamina, a meshwork of filaments lining the inner nuclear membrane

Microtubules

  • Composed of α-tubulin and β-tubulin dimers arranged in a hollow cylindrical structure
  • Measure 25 nm in diameter, making them the largest of the cytoskeletal components
  • Exhibit dynamic instability, constantly growing and shrinking
  • Provide structural support and maintain cell shape
  • Serve as tracks for intracellular transport of organelles and vesicles
  • Form the mitotic spindle during cell division, separating chromosomes
  • Organize the cytoplasm and determine the position of organelles (Golgi apparatus)

Cellular Appendages

Cilia

  • Short, hair-like projections extending from the cell surface
  • Composed of microtubules arranged in a 9+2 pattern (9 outer doublets and 2 central singlets)
  • Covered by the cell membrane and anchored by basal bodies
  • Beat in a coordinated manner to move fluids or particles along the cell surface
  • Found in large numbers on the surface of certain cells (respiratory tract epithelium)
  • Play a role in locomotion in some unicellular organisms (Paramecium)

Flagella

  • Long, whip-like projections extending from the cell surface
  • Composed of microtubules arranged in a 9+2 pattern, similar to cilia
  • Covered by the cell membrane and anchored by basal bodies
  • Beat in a wave-like motion to propel the cell through a liquid medium
  • Typically found in smaller numbers compared to cilia, often just one or a few per cell
  • Enable locomotion in sperm cells and some protozoans (Euglena)

Cell Movement

Cell Motility

  • The ability of cells to move and change their position
  • Involves the coordinated action of cytoskeletal components, particularly microfilaments
  • Occurs through the formation of pseudopodia, filopodia, or lamellipodia (different types of cytoplasmic protrusions)
  • Enables cells to migrate during embryonic development, wound healing, and immune responses
  • Plays a role in the metastasis of cancer cells, allowing them to invade other tissues
  • Facilitated by cell adhesion molecules (integrins) that interact with the extracellular matrix

Cytoplasmic Streaming

  • The movement of cytoplasm within a cell, often in a circular or directional manner
  • Driven by the activity of motor proteins, such as myosin, along microfilaments
  • Helps distribute nutrients, organelles, and other cellular components throughout the cell
  • Occurs in both prokaryotic and eukaryotic cells
  • Particularly prominent in large plant cells (Chara) where it enhances the distribution of chloroplasts
  • Assists in the rapid transport of materials within the cell, overcoming the limitations of diffusion

Key Terms to Review (21)

Cytokinesis: Cytokinesis is the final stage of cell division, where the cytoplasm of a parent cell is divided into two daughter cells. This process occurs after mitosis or meiosis, ensuring that each new cell contains the necessary organelles and cytoplasmic components for survival and function. Cytokinesis is essential for maintaining cellular organization and contributing to tissue growth and repair.
Live-cell imaging: Live-cell imaging is a powerful technique that allows scientists to observe and analyze living cells in real-time using various imaging technologies. This method enables researchers to study dynamic processes such as cell movement, division, and interactions within the cytoskeleton without disturbing the natural behavior of the cells. By providing insights into cellular functions and structures, live-cell imaging plays a crucial role in understanding cell movement and the organization of the cytoskeleton.
Pi3k signaling: PI3K signaling refers to a critical intracellular pathway that involves the activation of phosphoinositide 3-kinase (PI3K), which plays a significant role in cellular functions such as growth, proliferation, and survival. This pathway is vital for regulating various aspects of cell movement and the cytoskeleton, influencing how cells migrate, adhere, and respond to extracellular signals.
Rho GTPases: Rho GTPases are a family of small signaling GTPases that play crucial roles in regulating the cytoskeleton and cell movement. These proteins act as molecular switches that control various cellular processes, including the organization of actin filaments, cell adhesion, and motility. By cycling between an active GTP-bound state and an inactive GDP-bound state, Rho GTPases influence the dynamics of the cytoskeleton, which is essential for processes like cell migration and shape changes.
Immunofluorescence: Immunofluorescence is a laboratory technique that uses antibodies tagged with fluorescent dyes to detect and visualize specific proteins or antigens within cells or tissue sections. This method allows researchers to study the distribution and localization of proteins in relation to the cytoskeleton and cellular structures, providing insight into cell movement and signaling pathways.
Amoeboid movement: Amoeboid movement is a type of cell movement characterized by the extension and retraction of pseudopodia, allowing cells to change shape and move in a crawling manner. This movement is primarily facilitated by the cytoskeleton, which provides structural support and enables the dynamic reshaping of the cell membrane. Amoeboid movement is essential for various cellular processes, including locomotion, feeding, and immune responses in certain organisms.
Polymerization: Polymerization is the process through which small molecules, known as monomers, chemically bond together to form a larger, more complex structure called a polymer. This process is essential in the formation of various biomolecules, including proteins, nucleic acids, and polysaccharides, which play critical roles in cellular structure and function. In the context of cell movement, polymerization is especially relevant to the dynamics of the cytoskeleton, where it facilitates the assembly and disassembly of filamentous structures necessary for cellular motility and shape changes.
Cilia: Cilia are tiny, hair-like structures that extend from the surface of some eukaryotic cells, playing essential roles in cell movement and environmental interaction. They are composed of microtubules arranged in a specific pattern and are involved in various functions, such as locomotion and the movement of fluids across cell surfaces. The coordinated beating of cilia enables cells to propel themselves or move substances along their surfaces.
Actin: Actin is a globular protein that forms microfilaments, which are key components of the cytoskeleton in eukaryotic cells. These filaments play a crucial role in maintaining cell shape, enabling cell movement, and facilitating various cellular processes such as division and intracellular transport. Actin exists in two forms: G-actin (globular actin) and F-actin (filamentous actin), with the latter being the polymerized form that contributes to the structural framework of cells.
Depolymerization: Depolymerization is the process of breaking down a polymer into its monomer units or smaller oligomers. This process is crucial in various biological and cellular contexts, as it allows for the recycling of building blocks and regulation of polymer levels in the cell, especially within the cytoskeleton. The cytoskeleton, composed of dynamic structures like microtubules and actin filaments, relies on depolymerization for cell movement, shape changes, and various cellular functions.
Cell migration: Cell migration is the process by which cells move from one location to another within an organism, a fundamental aspect of development, immune response, and wound healing. This movement is closely linked to the cytoskeleton, which provides the structural framework that enables cells to change shape and move, highlighting the intricate interplay between cellular mechanics and biological functions.
Flagellar Movement: Flagellar movement refers to the locomotion of cells and organisms that utilize flagella, which are long, whip-like structures that protrude from the cell body. This type of movement is vital for the motility of various single-celled organisms, sperm cells, and some multicellular organisms, facilitating movement through liquid environments. Flagella generate thrust by rotating or undulating, powered by the motor proteins in the cell’s cytoskeleton, linking this movement to broader concepts of cellular structure and dynamics.
Pseudopodia: Pseudopodia are temporary, foot-like extensions of a cell's cytoplasm that enable movement and the capture of food. These structures play a crucial role in the locomotion of certain cells, particularly in amoebas and some white blood cells, allowing them to navigate their environments and engage in processes like phagocytosis.
Tubulin: Tubulin is a globular protein that serves as a building block for microtubules, which are essential components of the cytoskeleton in eukaryotic cells. This protein plays a critical role in maintaining cell shape, facilitating intracellular transport, and enabling cell division. Tubulin exists primarily in two forms, alpha-tubulin and beta-tubulin, which polymerize to form the hollow structures of microtubules that are crucial for cellular organization and movement.
Dynein: Dynein is a motor protein that moves along microtubules within cells, transporting cellular cargo towards the minus end of the microtubules. It plays a crucial role in various cellular processes such as vesicle transport, positioning organelles, and facilitating the movement of cilia and flagella, contributing significantly to cell movement and stability.
Intracellular transport: Intracellular transport refers to the movement of substances within a cell, utilizing structures such as the cytoskeleton and motor proteins. This process is crucial for distributing essential materials like organelles, proteins, and nutrients to different areas of the cell, ensuring proper function and maintenance. The efficiency of intracellular transport is vital for cell health, growth, and response to environmental changes.
Cell motility: Cell motility refers to the ability of cells to move and navigate their environment, a vital process for various biological functions such as development, immune response, and wound healing. This movement is primarily facilitated by the cytoskeleton, which provides structural support and enables dynamic changes in cell shape. Additionally, cell motility is crucial for processes like tissue formation, migration of immune cells toward infection sites, and the metastasis of cancer cells.
Flagella: Flagella are long, whip-like structures that protrude from the surface of certain cells, enabling movement through liquid environments. These structures are crucial for the motility of various organisms, particularly prokaryotic cells like bacteria, and they play a significant role in their ability to navigate their surroundings, find nutrients, and evade predators.
Microtubules: Microtubules are hollow, cylindrical structures made of tubulin protein that play critical roles in maintaining cell shape, facilitating intracellular transport, and enabling cell division. These dynamic filaments are part of the cytoskeleton, providing a scaffold that supports various cellular functions and structures, including organelles and vesicles. Their ability to rapidly grow and shrink allows them to adapt to the cell's needs during processes such as mitosis and motility.
Microfilaments: Microfilaments are thin, thread-like structures made of the protein actin, forming a part of the cytoskeleton in eukaryotic cells. They play a crucial role in maintaining cell shape, enabling cell movement, and facilitating various cellular processes such as division and intracellular transport. Microfilaments interact with other cytoskeletal components to create a dynamic framework that supports cellular functions.
Intermediate filaments: Intermediate filaments are a type of cytoskeletal structure found in eukaryotic cells, providing mechanical support and helping maintain the cell's shape. They are composed of various proteins that assemble into fibrous structures, playing a crucial role in the integrity of the cell and its organelles. Intermediate filaments connect to other cytoskeletal components, working alongside microtubules and actin filaments to facilitate cell stability and resilience against stress.