What is cytoskeleton?
I’m sure everyone has heard of cells before, but do you know what structure supports the cell's shape and internal organization? It's the cytoskeleton. The cytoskeleton can be compared to the bones of the human body, as it maintains the cell's internal organization and ensures proper functioning inside the cell. It is a network of fibers that extends throughout the cytoplasm, which is the gelatinous liquid that fills the cell's interior. This article will introduce the key roles of the cytoskeleton and its components.
What are the roles of the cytoskeleton?
Providing mechanical support: As mentioned earlier, the primary function of the cytoskeleton is to provide mechanical support and maintain the cell's shape, particularly in animal cells that lack the rigid cell walls found in plant cells. It achieves this through a delicate balance between opposing forces exerted by its components. Unlike human bones, the cell's cytoskeleton is highly flexible. It can rapidly disassemble in one part of the cell and reassemble in another location, thereby altering the cell's shape.
The cytoskeleton plays a crucial role in cell motility, which includes changes in cell location and movements of cell components. Successful cell motility relies on the interaction between the cytoskeleton and motor proteins. Cytoskeletal elements, along with motor proteins, collaborate with plasma membrane molecules to facilitate cell movement along extracellular fibers. Within the cell, vesicles and organelles often employ motor protein "feet" to traverse along cytoskeletal tracks and reach their destinations. For example, vesicles containing neurotransmitter molecules migrate to the tips of axons, the elongated extensions of nerve cells, where they are released as chemical signals to adjacent nerve cells. Additionally, the cytoskeleton manipulates the plasma membrane by inwardly bending it to form phagocytic vesicles or food vacuoles.
What are its components?
There are three main types of fibers that make up the cytoskeleton: the thickest microtubules, the thinnest microfilaments, and the intermediate filaments that have diameters in a middle range.
Microtubules: These hollow rods are present in all eukaryotic cells and are constructed from globular proteins called tubulins. Each tubulin protein is a dimer consisting of α-tubulin and β-tubulin subunits. Microtubules elongate by adding tubulin dimers. They have two distinct ends, with one end accumulating or releasing tubulin dimers at a higher rate during cellular activities. Microtubules play a vital role in chromosome separation during cell division, where they emanate from a centrosome. They also form structures like cilia and flagella found in some cells. When cells tightly adhere in tissue layers, cilia or flagella extensions propel fluid across the tissue surface. For example, the cilia lining the oviducts aid in moving an egg towards the uterus in the female reproductive tract.
Microfilaments (Actin Filaments): These filaments are composed of actin, a globular protein, and form a twisted double chain of actin subunits. Unlike microtubules that resist compression, microfilaments bear tension and pulling forces. They are involved in cell motility. Together with thicker filaments, they form myosin, which is responsible for muscle cell contraction. In some plant cells, microfilaments contribute to cytoplasmic streaming, the circular flow of cytoplasm within cells.
Intermediate filaments: Unlike microtubules and microfilaments found in all eukaryotic cells, intermediate filaments are only present in certain cell types. Each type of intermediate filament is constructed from specific molecular subunits belonging to a protein family, including keratin filaments found in dead skin cells.
In conclusion, cytoskeleton is crucial for maintaining the cell’s shape and internal structures. If the cytoskeleton becomes damaged, the loss of structural integrity can result in the cell’s susceptibility to external pressure and potential permanent damage, which leads to irreversible consequences.