What is the correct order of cytoskeletal filaments in decreasing filament diameter?
What is the correct order of cytoskeletal filaments in decreasing filament diameter? microtubules → intermediate filaments → microfilaments Myosin is a motor protein found attached to
What is the Assembly and stabilization of microfilaments called?
Assembly and stabilization of microfilaments (actin filaments). Actin binds ATP and begins assembly by binding to actin-related proteins (ARPs) that serve as a nucleation site, usually just under the cell membrane in the cortex of the cell.
Are motor proteins specific to the type of filament they bind?
No, motor proteins are specific for the type of filament they bind. the loss of integrin proteins from the cell's surface, or a change in the type of integrin proteins present on the cell's surface. If intermediate filaments were capable of dynamic instability, which of the following outcomes would be most likely?
How will a mouse without basal lamina be different from normal mice?
Imagine that you are examining a mouse that does not produce basal lamina in the skin. How will this mouse be different from a normal, wild-type mouse? The epidermis will not be connected to the dermis.
What is the best characterization of the minus end of a dynamic filament ls7c?
What is the best characterization of the minus end of a dynamic filament? It lengthens more slowly than the plus end.
Which layer of the extracellular matrix of a plant provides the greatest strength?
Which layer of the extracellular matrix of a plant provides the greatest strength? The epidermis is the outer layer and is under constant physical stress. This highly folded area between the epidermis and the dermis gives the epidermis additional support and protection against abrasive stress.
Which answer choice correctly describes the skin cell type it characterizes?
Which answer choice correctly describes the skin cell type it characterizes? Fibroblasts are a cell type found in the dermis of the skin; its primary function is to secrete extracellular matrix.
Which best describes a role that microfilaments play in the structure and function of red blood cells?
Which of the following best describes a role that microfilaments play in the structure and function of red blood cells? A., They anchor and orient the O2-bearing hemoglobin protein molecules.
What are the three general characteristics of connective tissue?
Structural Elements of Connective Tissue Connective tissues come in a vast variety of forms, yet they typically have in common three characteristic components: cells, large amounts of amorphous ground substance, and protein fibers.
How do plant cell walls and animal cell extracellular matrix compare?
Plants and fungi have a tough cell wall for protection and support, while animal cells can secrete materials into their surroundings to form a meshwork of macromolecules called the extracellular matrix.
Which characteristic of DNA makes it most suitable as a molecule for this role?
Which characteristic of DNA makes it most suitable as a molecule for this role? DNA is made of two strands of complementary nucleotides.
Which of the following best describes the cells that result from the process of meiosis in mammals?
Assuming that meiosis occurred in a mammal, which statement best describes the cells that resulted? They are genetically different from the parent cell.
Which of the following would be a factor limiting cell size quizlet?
which of the following would be a factor limiting cell size? Efficiency of moving material across the cell membrane, demands of DNA, the ratio of surface area to volume.
What is found at the minus end of an actin filament when it undergoes Treadmilling?
Cofilin functions by binding to ADP-actin on the negative end of the filament, destabilizing it, and inducing depolymerization. Profilin induces ATP binding to G-actin so that it can be incorporated onto the positive end of the filament.
What holds actin filaments at the minus ends as they polymerize outward?
The minus ends are frequently attached to the sides of other actin filaments by ARP complexes (see Figure 16-28), helping to form the two-dimensional web (Figure 16-88).
Which of the following protein fibers is used for cellular movement and are extremely thin in size?
Which of the following protein fibers is used for cellular movement and are extremely thin in size? Actin filaments are used in movement of the cell and are very thin fibers.
Why are actin filaments capped tightly?
Thus, the uniform (Gaussian) length distribution of the short RBC actin filaments suggests that they are capped tightly at both ends to prevent subunit loss or gain that would otherwise lead to filament length changes over the RBC lifetime (~ 120 days in humans, ~ 40 days in mice).
Which filaments of the muscle cell are fingerlike extensions of epithelial cells?
Actin filaments determine the shape and movement of the cell’s surface, including structures such as microvilli, which are fingerlike extensions of epithelial cells that line internal structures like the intestinal villi and kidney tubules.
What are the polar structures of actin filaments?
Actin filaments are polar structures, with each end differing in its equilibrium-binding constant for actin monomers (Fig. 172-3 ). Filaments grow at the high-affinity or barbed end, whereas depolymerization occurs at the low-affinity or pointed end. This difference, generated by the ability of actin to bind and hydrolyze adenosine triphosphate, provides a physical polarity that regulatory proteins use to drive filament dynamics with high temporal and spatial precision. Three classes of proteins regulate the availability of high-affinity actin filament ends: filament-nucleating proteins (e.g., ARP2/3 de novo nucleation), filament-capping proteins (e.g., gelsolin), and filament-severing proteins (e.g., cofilin). Actin-nucleating factors bind actin monomers under conditions otherwise unfavorable for assembly and generate a new filament with a free high-affinity end available for assembly. Actin filament-capping proteins bind to the high-affinity filament end and regulate the addition of monomers by their presence or absence at the end of the filament. Actin-binding proteins are regulated by various second messengers, including calcium. On stimulation, localized changes in the intracellular Ca 2+ concentration lead to the rapid initiation of actin assembly and disassembly. The changes in actin filament length and the extent of cross-linkage between the filaments may account for the directional extension of actin-rich lamellae and contraction of the tail-like uropod at the other end of the cell. Movement in the neutrophil is therefore the result of lamellar protrusions resulting from the growth of actin filaments. Actin-rich lamellae will continue to be maintained as long as the neutrophil detects the chemoattractant gradient.
How many different structures can actin filaments assemble into?
Actin filaments can assemble into at least 15 different structures in metazoan cells (Chhabra and Higgs, 2007) and distinct tropomyosin isoforms have been shown to mark some of these actin filament populations. A detail description of the subcellular localization of tropomyosin isoforms in various cell types both in vivo and in vitro can be found in Martin and Gunning (2008) and Martin and Gunning (2008). This review will focus on the tropomyosin isoforms and subcellular locations in the nervous system. Briefly, in nonneuronal cell types in vitro, both tropomyosin antibodies and tagged tropomyosin proteins show the existence of actin filaments associated with different tropomyosin isoforms in the lamellipodia, stress fibers and perinuclear region of fibroblasts, neuroblastoma, and C2C12 myoblasts cells ( Hillberg et al., 2006; Lin et al., 1988; Martin et al., 2010; Percival et al., 2000; Schevzov et al., 2005b, 2011 ), the adhesion belts in epithelial cells ( Temm-Grove et al., 1998 ), the apical and basal membranes of polarized epithelial cells ( Dalby-Payne et al., 2003 ), adhesion structures of bone-resorbing osteoclasts ( McMichael et al., 2006 ), and chicken auditory hair cells ( Drenckhahn et al., 1991 ). In addition, distinct temporal and spatial localization of tropomyosin isoforms was evident in dorsal stress fibers in osteosarcoma cells ( Tojkander et al., 2011 ). In the yeast actin cytoskeleton, tropomyosin (Cdc8) is localized in the actin cables and contractile rings but absent from the actin patches ( Skau and Kovar, 2010 ). Further, it is acetylated cdc8 in the contractile ring and nonacetylated cdc8 in the cables ( Coulton et al., 2010 ). In vivo, specific cytoskeletal tropomyosin isoform-containing filaments are found in the apical and basolateral regions of human colon epithelial cells ( Percival et al., 2000) and in the Z-line adjacent cytoskeleton present in skeletal muscle ( Kee et al., 2004; Vlahovich et al., 2008 ).
How long are actin filaments?
During assembly, actin filaments can elongate up to many microns in length, but the RBC actin filaments are less than 40 nm long ( Section 3.2 ). At steady state, actin monomers continue to associate and dissociate from filament ends, so that over time, purified actin filaments achieve an exponential length distribution with filaments of varying lengths ( Littlefield & Fowler, 1998 ). Thus, the uniform (Gaussian) length distribution of the short RBC actin filaments suggests that they are capped tightly at both ends to prevent subunit loss or gain that would otherwise lead to filament length changes over the RBC lifetime (~ 120 days in humans, ~ 40 days in mice). In the 1990s, I and my colleagues identified RBC Tmod1 and αβ-adducin as the pointed and barbed end actin filament capping proteins, respectively, supporting the idea that actin capping restricts RBC actin filament length ( Section 4 ). This is a nice example of how the unique properties of the RBC membrane (short filaments with abundant numbers of filament ends) enabled discovery of novel actin capping proteins and provided insights into the important problem of actin filament length regulation in all cells.
What are the structures that actin filaments are located on?
Actin filaments determine the shape and movement of the cell’s surface, including structures such as microvilli, which are fingerlike extensions of epithelial cells that line internal structures like the intestinal villi and kidney tubules.
How many monomers are in an actin filament?
Actin filaments are right-handed two-stranded helices, with ~13 monomers per turn (Figure 1 (b) ). Each monomer adds ~2.7 Å to the filament, so there are ~370 monomers per micron. All monomers are oriented in the same direction along the helix, making the filament polar. Due to the filament's arrow-like appearance when coated with myosin, the two ends are often called ‘barbed’ and ‘pointed’, respectively. The nucleotide-binding cleft faces the pointed end. Some refer to the barbed and pointed ends as ‘+’ and ‘−’, respectively.