Retta - L4 part 1

Cytoskeleton Overview

• The cytoskeleton consists of actin filaments, microtubules, and intermediate filaments, playing a crucial role in cell shape, movement, and division.
• It regulates diverse cellular functions such as polarization, migration, and proliferation.
• Cytoskeletal proteins can be visualized using Coomassie blue dye, demonstrating their filamentous structures.

Types of Cytoskeletal Filaments

• Actin filaments (microfilaments) are composed of the protein actin, essential for cell shape and movement.
• Microtubules consist of tubulin and are vital for maintaining cell structure and chromosome separation during mitosis.
• Intermediate filaments are formed from various proteins and provide mechanical strength.

Visualization Techniques

• Immunofluorescence microscopy can detect actin and tubulin using antibodies specific to each protein.
• Primary antibodies recognize target proteins while secondary antibodies, often labeled with fluorescent dyes, amplify detection.
• Direct fluorescence microscopy involves tagging proteins with fluorescent proteins (e.g., GFP) for real-time observation of cytoskeleton dynamics.

Mitosis and Cytoskeleton

• The mitotic spindle, composed of microtubules, is crucial for chromosome separation during mitosis.
• Cytokinesis, the division of the cytoplasm, relies on the actin cytoskeleton to form the contractile ring.

Cytoskeletal Functions

• Supports intracellular traffic of organelles like the Golgi apparatus and endoplasmic reticulum (ER) via actin.
• Maintains the stability and shape of the plasma membrane, enabling functions such as endocytosis.
• Provides mechanical linkage to withstand stress, allowing cells to respond to physical stretching and shear stress, particularly in endothelial cells.
• Plays a vital role in cell migration, essential for immune response, and in muscle contraction via interactions between actin and myosin.

Cell Protrusions and Stability

• Microvilli, supported by actin filaments, are crucial for increasing surface area in epithelial cells of the digestive system.
• The positioning of organelles like mitochondria is determined by microtubules, which facilitate their movement within the cell.

Coloring and Labeling

• Fluorescent dyes (e.g., Rhodamine, fluorescein) can be conjugated to phalloidin, allowing specific visualization of actin filaments.
• Different dyes emit distinct colors, allowing simultaneous detection of multiple components within the cell.

Summary of Cytoskeletal Components

• Intermediate filaments provide mechanical strength against stretching and shear stress.
• Microtubules position organelles and enable intracellular transport.
• Actin filaments define cell shape and are critical for motility and the formation of structures like microvilli.### Role of Intermediate Filaments
• Intermediate filaments provide mechanical resistance to cells.
• They are interconnected through specific connecting proteins at cell interfaces.
• These connecting proteins, described as "protein buttons," anchor cells together, creating a mechanical structure.

Dynamics of Cytoskeletal Filaments

• Cytoskeletal filaments offer structural integrity but are inherently dynamic and not stable.
• They continually undergo remodeling, forming and disassembling while fulfilling their cell functions.
• Disruption of cytoskeleton dynamics, such as through drug intervention, can lead to cell death.

Actin Filaments and Cytoskeleton Dynamics

• Actin filaments are critical for maintaining cell structure; blockage by agents like phalloidin disrupts dynamic processes.
• All cytoskeletal filaments feature a stable structure, but this structure changes over time due to continuous remodeling.

Composition of Cytoskeletal Filaments

• Each filament type consists of specific smaller protein subunits:
  • Actin filaments are made of actin proteins.
  • Microtubules are composed of tubulin.
  • Intermediate filaments consist of various proteins.
• Filaments are elongated structures made up of chains of globular protein subunits.

Nucleation Process

• Nucleation is the essential first step in filament formation, involving the interaction of initial subunits.
• Formation of a nucleus, where a few subunits (typically three) come together, is crucial for retaining structure.
• Following nucleation, additional subunits attach to elongate the filament.

Mechanical Properties of Filaments

• Each cytoskeletal filament type displays distinct mechanical properties and dynamics.
• While all filament types are dynamic, they exhibit different behaviors and response patterns in the cell.

Explore the structure, origin, and function of the cytoskeleton. This quiz covers key components like actin filaments, microtubules, and intermediate filaments, as well as their role in cellular processes such as polarization, migration, and proliferation.