Citoskeletono Celular: Microtúbulos, Filamentos de Actina, Motilidad Celular y Filamentos Intermedios

Understanding the Cell Cytoskeleton: Microtubules, Actin Filaments, Cell Motility, and Intermediate Filaments

The cell cytoskeleton is a complex, dynamic structure that provides cells with shape, organization, and mechanical support. It is composed of three main types of filaments: microtubules, actin filaments, and intermediate filaments. Each of these filaments plays a crucial role in the functioning of the cell, from maintaining cell structure to facilitating cell movement. In this article, we will delve into the world of the cell cytoskeleton, focusing on the subtopics of microtubules, actin filaments, cell motility, and intermediate filaments.

Microtubules

Microtubules are the largest of the three types of cytoskeletal filaments, with a diameter of around 25 nm. They are made up of α- and β-tubulin dimers, which bind in a head-to-tail manner to form protofilaments that associate laterally to create hollow tubes. Microtubules are nucleated from a specific intracellular location known as a microtubule-organizing center (MTOC). In nondividing cells, microtubules radiate out from the centrosome to provide the basic organization of the cytoplasm, including the positioning of organelles. In many types of cells, networks of microtubules are found beneath the cell cortex, which is the meshwork of membrane-associated proteins that supports and strengthens the plasma membrane.

Microtubules play a significant role in cell motility. For example, cilia and eukaryotic flagella move as a result of microtubules sliding along each other. Cross sections of these tail-like cellular extensions show organized arrays of microtubules. Additionally, microtubules are involved in the cycles of cell migration, which includes the formation of protrusions called lamellipodia at the front, new focal adhesions to strengthen attachment to the extracellular matrix, actomyosin activity to induce retraction at the rear, and focal adhesion disassembly to allow whole cell movement forward.

Actin Filaments

Actin filaments, also known as microfilaments, are the narrowest of the three types of cytoskeletal filaments, with a diameter of about 7 nm. They are made up of actin monomers, which can polymerize to form filaments with a double-helix structure. Actin filaments have directionality, meaning they have two structurally different ends. They serve as tracks for the movement of motor proteins like myosin.

Actin filaments are involved in many cellular events requiring motion. For instance, in animal cell division, a ring made of actin and myosin pinches the cell apart to generate two new daughter cells. In muscle cells, actin and myosin form organized structures called sarcomeres, which contract when the actin and myosin filaments slide past each other. Additionally, actin filaments can assemble and disassemble quickly, allowing them to play an important role in cell motility, such as the crawling of white blood cells in the immune system.

Cell Motility and the Role of the Cytoskeleton

The cytoskeleton plays a crucial role in cell motility. For example, cilia and flagella move as a result of microtubules sliding along each other. In cell division, actin filaments are involved in the pinching off of the cell membrane in the final step of cytokinesis. Actin filaments also play key structural roles in the cell. In most animal cells, a network of actin filaments is found in the region of cytoplasm at the very edge of the cell, which gives the cell shape and structure.

Intermediate Filaments

Intermediate filaments are a type of cytoskeletal element made of multiple strands of fibrous proteins wound together. They have an average diameter of 8 to 10 nm, between that of microfilaments and microtubules. Intermediate filaments come in a number of different varieties, each one made up of a different type of protein. One protein that forms intermediate filaments is keratin, a fibrous protein found in hair, nails, and skin. Unlike actin filaments, which can grow and disassemble quickly, intermediate filaments are more permanent and play an essentially structural role in the cell. They are specialized to bear tension and their jobs include maintaining the shape of the cell and anchoring the nucleus and other organelles in place.

Conclusion

The cell cytoskeleton is a complex and dynamic structure that provides cells with shape, organization, and mechanical support. It is composed of three main types of filaments: microtubules, actin filaments, and intermediate filaments. Each of these filaments plays a crucial role in the functioning of the cell, from maintaining cell structure to facilitating cell movement. Understanding the cell cytoskeleton and its subtopics is essential for understanding the basic functioning of living cells.