Microfilament: Structure, Function, and Location

Microfilaments or actin filaments comprise two intertwined strands of actin, a globular protein. The cytoskeleton anchors organelles in place; aids in endocytosis, the ingestion of foreign materials by a cell, and cytokinesis, the separation of daughter cells following cell division; and moves portions of the cell in growth and mobility processes. The prokaryotic cytoskeleton is involved in maintaining cell shape and polarity. There are different types of fibers present in the Eukaryotic Cytoplasm: Microfilaments, Intermediate filaments, and Microtubules. In this article, we will study microfilaments, their role in cytoplasm, and their structure and functions.

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Keyterms: Actin, Microfilaments, Protein, Cytoskeleton, Cell, Cytoplasm, Microtubules, Intermediate filaments, Fibers, Cell division, Cytokinesis

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What are microfilaments?

Microfilaments are double-stranded polymerized fibrous actin filaments; the monomeric form of the protein is globular (G) actin, and the two conditions coexist in the cell. They are lengthy chains of G-actin produced into two parallel polymers that have been twisted around each other into a helical orientation with a diameter of 6 to 8nm. The microfilaments are found in bundles, forming a three-dimensional (3D) intracellular meshwork. 

Microfilaments

These are found in all eukaryotic cells. They are primarily structural and are a vital component of the cytoskeleton, along with microtubules and, in some cases, intermediate filaments. They are the cytoskeleton's tiniest filaments. They perform various functions like cytokinesis, cell contractility, amoeboid movement, cell motility, endocytosis, exocytosis, change in cell shape, and mechanical stability.

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Role of Cytoplasm

The Cytoplasm is a rich semifluid that fills the spaces between cells. Except for the nucleus, the Cytoplasm in a eukaryotic cell mixes with all the rest cell contents. However, this does not occur in prokaryotic cells because they lack a distinct nuclear membrane, the Cytoplasm, containing the cell's genetic material. Compared to eukaryotes, the cells are smaller and have a more straightforward cytoplasm structure.

Microfilament and Cytoplasm

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Structure of Microfilaments

Microfilaments are predominantly made up of actin polymers. Actin appears globular when it is first generated by the cell. On the other hand, microfilaments appear as long polymerized chains of molecules interwoven in a helix, resulting in a filamentous form of the protein, i.e. F-actin. They are made up of two strands of actin subunits coiled in a spiral. Actin subunits that come together to create a microfilament are known as globular actin (G-actin). Once connected, they are known as filamentous actin (F-actin). They are the thinnest filaments, typically 7 nm in diameter. These polymers are rigid yet have a flexible framework. Microfilaments determine the shape and mobility of the cell's surface.

Structure of Microfilaments

Self-assembling of microfilaments

When three G-actin proteins join together to create a trimer, a microfilament begins to form. More actin then bonds to the barbed end. Autoclampin proteins, which operate as motors to assist construct the lengthy strands that makeup microfilaments, aid in the self-assembly process. A microfilament is formed by two long strands of actin arranged in a spiral.

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Function of Microfilaments

Microfilaments perform various functions such as:

1. As we know, Microfilaments are flexible; thus, in collaboration with myosin, they help to generate the forces required for cellular contraction and basic cell motions.
2. The integrity of actin filaments helps the eukaryotic cells survive environmental stress.
3. Microfilaments help in cell division during mitosis (cell division). Microfilaments aid in the process of cytokinesis, which occurs when a cell "pinches off" and physically divides into two daughter cells.
4. The microfilaments are also involved in amoeboid movements in some of the organisms.
5. Microfilaments, which are a component of the cytoskeleton, hold organelles in position within the cell. They are responsible for cell stiffness and form.
6. Microfilaments enable a cell to change its shape and move.

Function of Microfilaments

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Location of Microfilaments

Microfilaments are found at the cell's periphery, where they travel from the plasma membrane to the microvilli. They are present in bundles in this area, forming a three-dimensional intracellular meshwork. They are found in the pericanalicular zone, constructing pericanalicular web/meshwork.

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Things to remember

1. Microfilaments, also known as actin filaments, are protein filaments that comprise part of the cytoskeleton in the cytoplasm of eukaryotic cells. They are mostly made up of actin polymers.
2. Microfilaments, intermediate filaments, and microtubules make up the eukaryotic cytoskeleton.
3. The cytoskeleton organizes and maintains the form of the cell.
4. Microfilaments are found in all eukaryotic cells.
5. The microfilaments are found in bundles, forming a three-dimensional (3D) intracellular meshwork.
6. The polymers of microfilaments are simple to use and flexible but at the same time robust, resisting crushing and buckling while providing support to the cell.
7. They are the thinnest filaments, typically 7 nm in diameter.
8. They perform various functions like cytokinesis, cell contractility, amoeboid movement, cell motility, endocytosis, exocytosis, change in cell shape, and mechanical stability.
9. The integrity of actin filaments helps the eukaryotic cells survive environmental stress.
10. Microfilaments enable a cell to change its shape and move.

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