Actin is a cellular protein that forms monomeric subunits, which assemble into two intertwined strands to create the helical microfilament cables of the cytoskeleton.

Actin

Cytoplasmic streaming is the movement or circulation of cytoplasm within a eukaryotic cell, driven by the actions of actin microfilaments.

Cytoplasmic Streaming

Muscle contraction in animals is a cellular process in which actin filaments are pulled together by motor proteins, such as myosin, to shorten the length of muscle cells.

Muscle Contraction in Animals

During cytokinesis in animal cells, the cytoplasm is divided into two daughter cells by the formation of a cleavage furrow, which forms as a contractile ring of actin microfilaments that pinches the cell membrane.

Cleavage Furrow in Animal Cytokinesis

Microfilaments are dynamic eukaryotic cytoskeletal cables, measuring about 6 nm in diameter, composed of two intertwined strands of actin monomers that polymerize and depolymerize in response to cellular signals.

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In eukaryotic cells, the cytoskeleton is an internal network of fibers and tubes consisting of microfilaments, intermediate filaments, and microtubules. It provides structural support, anchors organelles, and serves as a transport network to move materials within the cell.

Eukaryotic Cytoskeleton

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Microfilaments

Intermediate filaments are diverse, relatively permanent cytoskeletal fibers with a diameter of $${}10\text{ nm}$$ (thicker than actin but thinner than microtubules) that are composed of multiple strands of polymerized subunits and function to maintain the position of the nucleus, form the nuclear lamina, and anchor cells together in animal tissues.

Intermediate Filaments

Microtubules are dynamic eukaryotic cytoskeletal structures composed of tubulin dimers (alpha-tubulin and beta-tubulin) that form hollow tubes with a diameter of $${}23\text{ nm}$$. They serve as internal support structures, transport tracks for organelles and vesicles, components of flagella and cilia, and form the mitotic spindle during cell division.

Microtubules

Exocytosis is the process by which secretory vesicles move toward and fuse with the plasma membrane to release their contents outside the cell. Cells utilize exocytosis to eliminate waste products and to secrete chemical signals that other cells can receive.

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