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Cell Signaling and 4 Types of Cell ...
Table of Contents
- What are intermediate filaments?
- Types of intermediate filaments
- General Structure of intermediate filaments
- Assembly of intermediate filaments
- Intermediate filaments During Mitosis
- Proteins Associated With Intermediate Filaments
- Intermediate filaments function
- Intermediate filaments (IFs) are robust and long-lasting protein fibres found in the cytoplasm of the majority of higher eukaryotic cells.
- 8 nm to 10 nm in diameter, which is “intermediate” between thin and thick filaments in muscle cells, where they were first described; their diameter is also between microfilaments (actin filaments) and microtubules.
- The IFs are resistant to colchicine and cytochalasin B but susceptible to proteolysis. In the majority of animal cells, IFs form a “basket” around the nucleus and stretch outward in gently curved arrays.
- IFs are especially abundant in areas where cells are subjected to mechanical stress, such as in epithelia, where they are interconnected at desmosomal junctions, along the length of axons, and throughout the cytoplasm of smooth muscle cells.
- Different names have been given to intermediate filaments based on the type of cell in which they are seen.
- Therefore, IFs in epidermal cells are known as tonofilaments, IFs in nerve cells are known as neurofilaments, and IFs in neuroglial cells are known as glial filaments.
- Intermediate filaments have a tubular look in cross-section. Each tubule appears to be composed of four or five protofilaments aligned parallel to one another.
- IFs are made of polypeptides whose sizes vary surprisingly widely (from about 40,000 to 130,000 daltons).
Types of intermediate filaments
The intermediate filaments are extremely varied in terms of their biochemical properties, but can be classified into four major kinds based on their morphology and localization:
1. Type I IF proteins
- Two subfamilies of keratin (also called tono, perakeratin, or cytokeratin) are typically present in epithelial cells: acidic keratin and neutral or basic keratin.
- Keratin filaments are always heteropolymers composed of an equal number of subunits from each subfamily of keratin.
- The keratins are the most complex class of intermediate filament (IF) proteins, having at least 19 different forms in human epithelia and 8 more in hair and nail keratins.
- Mammalian cytokeratins are -fibrous proteins that are generated in cells of live epidermis layers and compose the majority of stratum corneum’s dead layers.
2. Type II IF proteins
- Four types of polypeptides are present: vimentin, desmin, synemin, and glial fibrillary acidic protein (or glial filaments).
- Desmin is found in both striated (skeletal and cardiac) and smooth muscle cells. Vimentin is broadly dispersed in cells of mesenchymal origin, including fibroblasts, blood vessel endothelial cells, and white blood cells.
- In the nervous system, glial cells such as astrocytes and some Schwann cells include glial filaments.
- Synemin is a 230,000-dalton protein that, together with desmin and vimentin, is present in the intermediate filaments of muscle. IFs containing vimentin and synemin can be found in chicken erythrocytes.
- Each of these IF proteins prefers to self-assemble in vitro to create homopolymers and co-assembles with other Types II IF proteins to form co-polymers and heteropolymers.
- Some types of cells have co-polymers of vimentin and desmin, or vimentin and glial fibrillary acidic protein. Desmin, for instance, stays concentrated in the Z-lines and T-tubule system of the striated or skeletal system, alongside vimentin, synemin, and – actemin.
- Since desmin connects actin to plasma memberane, Lazarides and colleagues derived the name desmin from this fact in 1976. (in Greek desmin means link or bond).
3. Type III IF proteins
- Neurofilament proteins are the IF proteins that assemble form neurofilaments, a key cytoskeletal component in nerve axons and dendrites.
- The so-called neurofilament triplet consists of three different polypeptides in vertebrates.
4. Type IVIF proteins
- The nuclear lamins are the filamentous two-dimensional sheets that are so well-organized.
- At a certain point in the mitotic process, these filaments quickly breakdown and reassemble.
Characteristics of four types of intermediate filament proteins
|Types of intermediate filaments||Component polypeptide (mass in daltons)||Cellular location|
|Type I||Acidic keratins (40,000—70,000) Neutral or basic keratins (40,000—70,000)||Epithelial cells and epidermal derivatives such as hair and nail|
|Type II||Vimentin (53,000)|
Glial fibrillar acidic protein (glial filaments; 45,000)
|Many cells of mesenchymal origin|
Glial cells (astrocytes and some Schwann cells)
|Type III||Neurofilament proteins (about 130,000, 100,000 and 60,000)||Neurons|
|Type IV||Nuclear lamins A, B and C (65,000—75,000)||Nuclear lamina of all cells|
- Although cytoplasmic IF proteins range greatly in size, they are all encoded by the same multigene family.
- Based on their respective amino acid sequences, it may be deduced that the middle 310 amino acid residues of each IF polypeptide chain form an extended α -helix with three brief α -helical disruptions.
Assembly of intermediate filaments
The following are the processes typically assumed to be taken during construction of an intermediate filament according to current models:
- A dimer is formed when two identical monomers join together to form a coiled coil, with the conserved helical core sections oriented in parallel. The two dimers then align next to one another, forming a protofilament of 48 nm by 3 nm that is comprised of four polypeptide chains.
- The further association of these protofilaments results in progressively more complex structures.
- It is hypothesised that the intermediate filament, which has a diameter of 10 nm, is made up of 8-protofilaments (i.e., 32 polypeptide chains) that are linked end-on-end to neighbours by staggered overlap. If IFs are polar structures (like actin and tubulin) or non-polar structures is still unknown (like the DNA double helix).
- Epithelial cells in culture undergo dramatic alterations in their intermediate filaments of cytokeratin and vimentin during mitosis.
- The 10 nm filaments unravel into 2–4 nm threads and form spheroidal aggregates of both types of proteins during prophase.
- Most vimentin and cytokeratin are found in spheroid bodies during metaphase and anaphase, and the filamentous cytoskeleton is gradually rebuilt during telophase.
- Franke (1982) drew the conclusion from these experiments that living cells include elements that facilitate the reversible disintegration and restoration of intermediate filaments during mitosis.
Proteins Associated With Intermediate Filaments
- Several proteins bind intermediate filaments and connect them to membranes and other polymers in the cytoskeleton.
- Nuclear lamins are tethered to the nuclear membrane by integral membrane proteins known as nuclear envelope transmembrane proteins.
- Keratin filaments in the skin’s outer layers are aggregated by filaggrin’s mediation. Plakins are large proteins that serve as binding sites for cytoskeletal polymers and sticky junction proteins, thereby connecting cytoskeletal components and membranes.
- Plectin, like many other plakins, is comprised of a 200-nm coiledcoil with globular domains at either end. Plectin can crosslink intermediate filaments to one another, to actin filaments, and to microtubules via binding sites in both globular domains.
- Rare muscular dystrophy with blistering skin is caused by recessive mutations in human plectin. Having the null mutation in mice is fatal.
- At desmosomes and hemidesmosomes, plectin and two additional plakins connect keratin filaments to three distinct plasma membrane adhesion proteins.
- Desmoplakin also acts like a cadherin to secure keratin filaments to desmosomes. Plakin BPAG1e (bullous pemphigoid antigen 1-e) binds keratin filaments to the transmembrane protein BPAG2, while plectin 1a links keratin to 4-integrins at hemidesmosomes (bullous pemphigoid antigen 2).
- Some people who suffer from neuropathies or a specific type of epidermolysis bullosa have mutations in the dystonin gene, which is expressed in multiple splice variants.
- Most intermediate filaments’ primary role is to give the cell and its nucleus structural support.
- The transcellular network formed by IFs in epithelia appears to be geared toward withstanding mechanical stress.
- The long, skinny cylinders of cytoplasm in nerve cells (axons) are protected by neurofilaments against stresses brought on by the animal’s movement.
- The sarcomeres of muscle cells are supported mechanically by desmin filaments, while the enormous lipid droplets in adipose tissue are surrounded by vimentin filaments.
- Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. Intermediate Filaments. Available from: https://www.ncbi.nlm.nih.gov/books/NBK9834/
- Intermediate Filaments. (2017). Cell Biology, 613–622. doi:10.1016/b978-0-323-34126-4.00035-9
- Eng, D. L., & Eng, L. F. (2009). Intermediate Filaments. Encyclopedia of Neuroscience, 173–178. doi:10.1016/b978-008045046-9.01010-x
- Bomont, P. (2016). Degradation of the Intermediate Filament Family by Gigaxonin. Intermediate Filament Associated Proteins, 215–231. doi:10.1016/bs.mie.2015.07.009
- Herrmann, H., Bär, H., Kreplak, L. et al. Intermediate filaments: from cell architecture to nanomechanics. Nat Rev Mol Cell Biol 8, 562–573 (2007). https://doi.org/10.1038/nrm2197
- Zamoner, A., & Pessoa-Pureur, R. (2017). Intermediate Filaments as a Target of Signaling Mechanisms in Neurotoxicity. In (Ed.), Cytoskeleton – Structure, Dynamics, Function and Disease. IntechOpen. https://doi.org/10.5772/66926
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What is the structure of the intermediate filament? ›
Intermediate filaments are composed of smaller strands in the shape of rods. Eight rods are aligned in a staggered array with another eight rods, and these components all twist together to form the rope-like conformation of an intermediate filament.What best describes an intermediate filament? ›
Intermediate filaments, in contrast to actin filaments and microtubules, are very stable structures that form the true skeleton of the cell. They anchor the nucleus and position it within the cell, and they give the cell its elastic properties and its ability to withstand tension.What is the meaning of intermediate filaments? ›
Intermediate filaments (IF) are proteins which are primordial components of the cytoskeleton and the nuclear envelope. They generally form filamentous structures 8 to 14 nm wide and intermediate in size between microtubules and microfilaments.What is the function of intermediate filaments quizlet? ›
Intermediate filaments have great tensile strength, and their main function is to enable cells to withstand the mechanical stress that occurs when cells are stretched.What is the structure and function of microfilaments? ›
Microfilaments, also called actin filaments, as they consist of two intertwined strands of a globular protein known as actin. They are the polymers of the protein actin and are smallest filaments of the cytoskeleton. They have a vital role in cell movements, cell division, and muscle contraction.What is the function of intermediate filaments in cytoskeleton? ›
Intermediate filaments (IFs) are a key component of the cytoskeleton in virtually all vertebrate cells, including those of the lens of the eye. IFs help integrate individual cells into their respective tissues.What do intermediate filaments regulate? ›
Intermediate filaments regulate nucleus rigidity
Thus, alterations of nucleus rigidity affect the cell ability to squeeze in between matrix fibers. Lamins are the type IV intermediate filament proteins that are the major components of the nuclear membrane  and largely affect the mechanical property of the nucleus.
Epithelia are exposed to multiple forms of stress. Keratin intermediate filaments are abundant in epithelia and form cytoskeletal networks that contribute to cell type–specific functions, such as adhesion, migration, and metabolism. A perpetual keratin filament turnover cycle supports these functions.What are intermediate filaments in biology simple? ›
Intermediate filaments function primarily as flexible intracellular tendons (analogous to nylon rope) that prevent excessive stretching of cells that are subjected to external or internal physical forces.What is intermediate filaments made of? ›
The intermediate filaments comprise the major component of the cytoskeleton and consist of five major subgroups—vimentin, keratins, desmin, neurofilaments, and glial fibrillary acidic protein (GFAP)—and a small number of minor subgroups (e.g., nestin, peripherin).
What is the function of filament? ›
The main function that filament performs is to carry nutrients to the anther for the development of the anther and pollen grains.What is intermediate structure? ›
Intermediate structures means vehicle components to which the partitioning system is attached to the prescribed vehicle(s) which do not constitute the anchorages.Are intermediate filaments responsible for movement? ›
Intermediate filaments have no role in cell movement. Their function is purely structural. They bear tension, thus maintaining the shape of the cell, and anchor the nucleus and other organelles in place.What are the key functions of microfilaments? ›
Microfilaments assist with cell movement and are made of a protein called actin. Actin works with another protein called myosin to produce muscle movements, cell division, and cytoplasmic streaming. Microfilaments keep organelles in place within the cell.
Intermediate Filaments Definition. strong polymers of fibrous polypeptides that resist stretch and play a structural (tension-bearing) function, Found in most, but not all cell types.What is the structure of microfilaments? ›
Microfilaments are composed of two strands of subunits of the protein actin (hence the name actin filaments) wound in a spiral. Specifically, the actin subunits that come together to form a microfilament are called globular actin (G-actin), and once they are joined together they are called filamentous actin (F-actin).What is structure of microfilaments and microtubules? ›
The structure of the microfilaments is double helix. The structure of the microtubules is helical lattice. 2. Microfilaments are composed of the contractile proteins called as actin. Microtubules are composed of the subunits of a protein tubulin.What is a function of microtubules and microfilaments? ›
Microtubules, with intermediate filaments and microfilaments, are the components of the cell skeleton which determinates the shape of a cell. Microtubules are involved in different functions including the assembly of mitotic spindle, in dividing cells, or axon extension, in neurons.What is the structure and function of the cytoskeleton? ›
The cytoskeleton is a network of fibers forming the "infrastructure" of eukaryotic cells, prokaryotic cells, and archaeans. In eukaryotic cells, these fibers consist of a complex mesh of protein filaments and motor proteins that aid in cell movement and stabilize the cell.What is the difference between microfilaments and intermediate filaments? ›
Intermediate filaments are about 10 nm diameter and provide tensile strength for the cell. In the epithelial (skin) cells of the intestine, all three types of fibers are present. Microfilaments project into the villi, giving shape to the cell surface.
Why are intermediate filaments called that? ›
Initially designated 'intermediate' because their average diameter (10 nm) is between those of narrower microfilaments (actin) and wider myosin filaments found in muscle cells, the diameter of intermediate filaments is now commonly compared to actin microfilaments (7 nm) and microtubules (25 nm).What is the function of intermediate filaments in smooth muscle cells? ›
The intermediate filament (IF) network is one of the three cytoskeletal systems in the cell. IFs are widely distributed from the plasma membrane to the nucleus, providing mechanical and structural integrity for the cell (14; 38; 63).What is the structure of filament? ›
Each filament is a twisted chain of identical globular actin molecules, all these molecules point in the same direction along the axis of the chain. Therefore an actin filament has a structural polarity, with a plus and a minus end. Actin filaments are thinner,more flexible, and generally shorter than microtubules.What is the difference between actin and intermediate filaments? ›
The cytoskeleton of a cell consists of microtubules, actin filaments, and intermediate filaments. Microtubules are the largest of the three types of cytoskeletal fibres. They are made up of tubulin protein filaments. In contrast, actin filaments are the smallest, and they are made up of actin protein filaments.Are intermediate filaments organelle? ›
Intermediate filaments are found throughout the cell and hold organelles in place.What are two functions of filament? ›
The function of the filament is simply to hold up the anther, extending it up to an accessible part of the flower for pollinators reach, or for the wind to disperse the pollen.What is structure and function of a filament in flower? ›
Filament is a stalk-like structure that attaches to the base of the flower and supports the anther, which is the structure that produces pollen.What is the definition of filament in biology? ›
filament. noun. fil·a·ment ˈfil-ə-mənt. : a single thread or a thin flexible threadlike object, process, or appendage. especially : an elongated thin series of cells attached one to another or a very long thin cylindrical single cell (as of some algae, fungi, or bacteria)
It brings together various aspects of the curriculum into meaningful association through a focus on broad student selected themes of study. It reflects the interdependent nature of the real world and engages the learner in real life experiences, in a more holistic manner.Are intermediate filaments purely structural? ›
Intermediate filaments consist of several intertwined strands of fibrous proteins. Intermediate filaments have no role in cell movement. Their function is purely structural. They bear tension, thus maintaining the shape of the cell, and anchor the nucleus and other organelles in place.
What does intermediate mean in biology? ›
An intermediate is a molecule that is formed from two or more reactants and then reacts further to give products. Most chemical reactions require more than one step, and an intermediate is the product of each step, except for the last one, after which the final products are produced.Are intermediate filaments thick or thin? ›
Intermediate filaments (IFs) are 10nm in diameter and, therefore, intermediate in thickness between microfilaments and myosin thick filaments, or microfilaments and microtubules.What are intermediate filaments made up of? ›
The intermediate filaments comprise the major component of the cytoskeleton and consist of five major subgroups—vimentin, keratins, desmin, neurofilaments, and glial fibrillary acidic protein (GFAP)—and a small number of minor subgroups (e.g., nestin, peripherin).Is intermediate filament structurally polar? ›
The subunits of intermediate filaments are elongated, not globular, and are associated in an antipolar manner. As a result, the overall filament has no polarity, and therefore no motor proteins move along intermediate filaments. Intermediate filaments are found only in complex multicellular organisms.What is the formation of intermediate filaments? ›
To form an intermediate filament, vimentin molecules first form dimers which then assemble to form tetramers that then associate laterally and longitudinally to assemble into mature 10nm-wide filaments of varying lengths.What is the function of filament protein? ›
In biology, a protein filament is a long chain of protein monomers, such as those found in hair, muscle, or in flagella. Protein filaments form together to make the cytoskeleton of the cell. They are often bundled together to provide support, strength, and rigidity to the cell.What is a filament short answer? ›
A filament is the thin wire inside a light bulb that emits light when heated by an electric current. The incandescent light bulb makes light by heating a metal filament wire to a high temperature until it glows.What do intermediate filaments do simple? ›
The primary function of intermediate filaments is to create cell cohesion and prevent the acute fracture of epithelial cell sheets under tension.What is the unique role of intermediate filaments? ›
With unique assembly-disassembly dynamics and physical properties, cytoplasmic intermediate filaments play an important role in regulating cell shape and mechanical integrity.