Which end of a filament depolymerizes fastest?
If filaments are rapidly diluted so that the free subunitconcentration drops below the critical concentration, the fast-growing end also depolymerizes fastest. The more dynamic of the two ends of a filament, where both growth and shrinkage are fast, is called the plus end, and the other end is called the minus end.
What determines the polarity of actin filaments and microtubules?
The structural polarity of actinfilaments and microtubules is created by the regular, parallel orientation of all of their subunits. This orientation makes the two ends of each polymerdifferent in ways that have a profound effect on filament growth rates.
Do cytoskeletal filaments self-assembly?
The Self-Assembly and Dynamic Structure of Cytoskeletal Filaments Three types of cytoskeletal filaments are common to many eucaryotic cells and are fundamental to the spatial organization of these cells.
What are the mechanical properties of actin tubulin and intermediate filament?
Mechanical properties of actin, tubulin, and intermediate filament polymers. Networks composed of microtubules, actin filaments, or a type of intermediate filament called vimentin, all at equal concentration, were exposed to a shear force in a viscometer, (more...)
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.
Can melanin granules be moved by dynein and kinesin along actin microfilament?
Could melanin granules be moved by dynein and kinesin along an actin microfilament? No, these motor proteins are specific to microtubules and cannot move along microfilaments.
What correctly describes the role of cell junctions?
What correctly describes the role of cell junctions? Adherens junctions are cell junctions that anchor cells to other cells.
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 type of cellular junction s allow s for the movement of proteins and transfer RNA molecules?
Gap junctions and plasmodesmata have what feature in common? They both allow direct transport of materials between cells. They both attach to the cytoskeleton. They both are made up of protein subunits located in the plasma membrane.
Which one of the cytoskeletal elements is associated with providing the cell with mechanical strength?
Intermediate filaments provide mechanical strength and resistance to shear stress. Microtubules determine the positions of membrane-enclosed organelles and direct intracellular transport. Actin filaments determine the shape of the cell's surface and are necessary for whole-cell locomotion (Panel 16-1).
Which type of junctions must there be between cells to form a barrier?
Tight junctions make solid connections between adjacent cells. These cells form a solid barrier.
Which type of cell junction are tight junctions quizlet?
Tight Junctions (Occluding Junctions) Function and Mechanism: To prevent molecules and particles on one side of an epithelial sheet from seeping between cells to reach the other side of the epithelium. Occludin in one cell spans the plasma membrane and links to occludin from the adjacent cell.
What type of cell junction is found in the epithelium of the skin and allows for the tissue to stretch and bend?
Short proteins called cadherins in the plasma membrane connect to intermediate filaments to create desmosomes. The cadherins join two adjacent cells together and maintain the cells in a sheet-like formation in organs and tissues that stretch, like the skin, heart, and muscles.
Which of the following actions correctly describe a role performed by at least one type of intercellular connection?
Which of the following actions correctly describe a role performed by at least one type of intercellular connection? Forms a watertight barrier between the cells.
Which phase of the cell cycle has the greatest number of cells in the treated sample?
The treated cells are mostly in the G1 phase (region A), but in the control sample, there are peaks of cells in both G1 and G2 (region C).
What are the major layers of the skin what structural components are in each layer?
Skin has three layers: The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone. The dermis, beneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands. The deeper subcutaneous tissue (hypodermis) is made of fat and connective tissue.
What play an important role in cell division and they are made of?
Centrosomes are organelles that contain centrioles, which play an important role in cell division.
How do cells connect to the extracellular matrix?
Cells also connect to a common set of extracellular fibers called the extracellular matrix through receptors called integrins. Cells in a tissue communicate via their adhesion complexes and gap junctions.
What moves large particles and fluid droplets across the cell membrane?
Endocytosis is a type of active transport that moves particles, such as large molecules, parts of cells, and even whole cells, into a cell. There are different variations of endocytosis, but all share a common characteristic: the plasma membrane of the cell invaginates, forming a pocket around the target particle.
Which information would accurately describe the difference between active and passive transport?
In passive transport, the molecules move against (up) the concentration gradient. D. In active transport, a molecule moves from an area of greater concentration to an area of lesser concentration.
Why does the epidermis need to send signals to the dermis?
The epidermis needs to send signals to the dermis, the highly folded area increases the surface area and hence the amount of signals that can reach the dermis.
What type of cell is used to coat the surface of a petri dish?
Many scientists use a specific type of mouse cell to coat the surface of petri dishes. These cells form a layer on which other kinds of cells, often of different species, can adhere and grow. The mouse cells used to coat petri dishes are likely:
Where is the extracellular matrix found?
a specialized form of the extracellular matrix found beneath all epithelial tissues.
Is the symlink slow growing?
It is slow growing, and also loses its subunits quickly.
How does filament depolymerization work?
Likewise, filament depolymerization proceeds spontaneously when this free energy change is greater than zero. A cell can couple an energetically unfavorable process to these spontaneous processes; thus, the free energy released during spontaneous filament polymerization or depolymerization can be used to do mechanical work—in particular, to push or pull an attached load. For example, elongating microtubules can help push out membranes, and shrinking microtubules can help pull mitotic chromosomes away from their sisters during anaphase. Similarly, elongating actinfilaments help protrude the leading edge of motile cells, as we discuss later.
What are intermediate filaments made of?
Intermediate filaments are made up of smaller subunits that are themselves elongated and fibrous, whereas actinfilaments and microtubules are made of subunits that are compact and globular—actin subunitsfor actin filaments, tubulinsubunitsfor microtubules. All three types of cytoskeletal filaments form as helical assemblies of subunits (see Figure 3-27), which self-associate, using a combination of end-to-end and side-to-side proteincontacts. Differences in the structures of the subunits and the strengths of the attractive forces between them produce critical differences in the stability and mechanical properties of each type of filament.
How do actinfilaments and microtubules form polarity?
The structural polarity of actinfilaments and microtubules is created by the regular, parallel orientation of all of their subunits. This orientation makes the two ends of each polymerdifferent in ways that have a profound effect on filament growth rates. Addition of a subunitto either end of a filament of nsubunits results in a filament of n+ 1 subunits. In the absence of ATP or GTP hydrolysis, the free energy difference, and therefore the equilibriumconstant (and the critical concentration), must be the same for addition of subunits at either end of the polymer. In this case, the ratio of the forward and backward rate constants, kon/koff, must be identical at the two ends, even though the absolute values of these rate constants may be very different at each end.
How do protein subunits form filaments?
The addition of each subunit to the end of the polymercreates a new end to which yet another subunit can bind. However, the robust cytoskeletal filaments in living cells are not built by simply stringing subunits together in this way in a single straight file. A thousand tubulinmonomers, for example, lined up end to end, would be enough to span the diameter of a small eucaryotic cell, but a filament formed in this way would not have enough strength to avoid breakage by ambient thermal energy, unless each subunit were bound very tightly to its neighbor. Such tight binding would limit the rate at which the filaments could disassemble, making the cytoskeletona static and less useful structure.
What are the structures of eucaryotic cells?
Regulation of the dynamic behavior and assembly of the cytoskeletal filaments allows eucaryotic cells to build an enormous range of structures from the three basicfilament systems. Micrographs that reveal some of these structures are shown in Panel 16-1. Microtubules, which are frequently found in a star-like cytoplasmic array emanating from the center of an interphasecell, can quickly rearrange themselves to form a bipolar mitotic spindleduring cell division. They can also form motile whips called ciliaand flagellaon the surface of the cell, or tightly aligned bundles that serve as tracks for the transport of materials down long neuronal axons. Actin filaments form many types of cell-surface projections. Some of these are dynamic structures, such as the lamellipodiaand filopodiathat cells use to explore territory and pull themselves around. Others are stable structures such as the regular bundles of stereociliaon the surface of hair cells in the inner ear, which tilt as rigid rods in response to sound. Inside cells, actinfilaments can also form either transient or stable structures: the contractile ring,for example, assembles transiently to divide cells in two during cytokinesis; more stable arrays allow cells to brace themselves against an underlying substratumand enable muscle to contract. Intermediate filaments line the inner face of the nuclear envelope, forming a protective cage for the cell's DNA; in the cytosol, they are twisted into strong cables that can hold epithelial cell sheets together, help neuronal cells to extend long and robust axons, or allow us to form tough appendages such as hair and fingernails.
What are the three types of cytoskeletal filaments?
Three types of cytoskeletal filaments are common to many eucaryotic cells and are fundamental to the spatial organization of these cells. Intermediate filamentsprovide mechanical strength and resistance to shear stress. Microtubulesdetermine the positions of membrane-enclosed organelles and direct intracellular transport. Actin filamentsdetermine the shape of the cell's surface and are necessary for whole-cell locomotion (Panel 16-1). But these cytoskeletal filaments would be ineffective on their own. Their usefulness to the cell depends on a large number of accessory proteins that link the filaments to other cell components, as well as to each other. This set of accessory proteinsis essential for the controlled assembly of the cytoskeletal filaments in particular locations, and it includes the motor proteinsthat either move organelles along the filaments or move the filaments themselves.
Why are short oligomers unstable?
Short oligomers composed of a few subunits can assemble spontaneously, but they are unstable and disassemble readily because each monomeris bonded only to a few other monomers. For a new large filament to form, subunits must assemble into an initial aggregate, or nucleus, that is stabilized by many subunit-subunit contacts and can then elongate rapidly by addition of more subunits. The initial process of nucleus assembly is called filament nucleation, and it can take quite a long time, depending on how many subunits must come together to form the nucleus. The instability of smaller aggregates creates a kinetic barrier to nucleation, which is easily observed in a solution of pure actinor tubulin—the subunits of actin filaments and microtubules, respectively. When polymerization is initiated in a test tube containing a solution of pure individual subunits (by raising the temperature or raising the salt concentration), there is an initial lag phase, during which no filaments are observed. During this lag phase, however, nuclei are assembling slowly, so that the lag phase is followed by a phase of rapid filament elongation, during which subunits add quickly onto the ends of the nucleated filaments (Figure 16-5A). Finally, the system approaches a steady state at which the rate of addition of new subunits to the filament ends is exactly balanced by the rate of subunit dissociation from the ends. The concentration of free subunits left in solution at this point is called the critical concentration, Cc. As explained in Panel 16-2, the value of the critical concentration is equal to the rate constant for subunit loss divided by the rate constant for subunit addition—that is, Cc= koff/kon.