Microfilaments and Intermediate Filaments
Terms
undefined, object
copy deck
- What are Actin-related proteins(Arps)? Name a common Arp.
-
Exhibit 50% sequence similarity with actin and stimulate actin assembly.
Arp2/3 complex binds at a 70 deg to the side of an actin filament to nucleate a daughter filament. - What is the calponin homology-domain superfamily?
- Actin cross-linking proteins whose sequence is homologous to that of calponin, a muscle protein.
- What mechanisms comprise cell locomotion?
-
Assembly of actin filaments and the formation of actin-filament bundles and networks.
Contraction of bundles of actin and myosin and thee sliding of single myosin molecules along an actin filament. - What is chemotaxis?
- Movement of a cel or organism toward or away from certain chemicals.
- What are contractile bundles?
- Bundles of actin and myosin in nonmuscle cells that function in cell adhesion (e.g., stress fibers) or cell movement (contracile ring in dividing cells).
- What is the critical concentration?
- The concentration of G-actin subunits where steadystate has been achieved in the growth of F-actin fibers, e.g. they remain the same length.
- What is the cytoskeleton? What is it's function?
-
Network of fibrous elements, consisting primarily of microtubules, actin microfilaments, and intermediate filaments, found in the cytoplasm of eukaryotic cells.
The cytoskeleton provides structureal support for the cell and permits directed movements of organelles, chromosomes, and the cell itself. - What is F-actin?
- Filaments composed of G-actin subunits.
- What is G-actin?
- The monomeric globular form of an abundant structural protein found in eukaryotic cells. The subunit of F-actin.
- What are intermediate filaments? What are three of their uses
-
Cytoskeletol fiber (10 nm dia) formed by poymerization fo serveral types of subunit proteins including keratins, lamins, and vimentin.
Intermediate filaments constitute the major structural proteins of skin and hair.
The form the scaffold that holds Z disks and myofibrils in place in muscle.
The provide support for cellular machines. - What are keratins?
- A group of intermediate filament proteins found in epithelial cells that assemble into heteropolymeric filamnents.
- What is a lamellipodium?
- A region of a cell protruding on the leading edge. It is composed of cross-linked actin-filament bundles and networks.
- What is a lamin? To which group does this belong?
-
Group of long flexible proteins that bind to other components of extracellular matrix (collagen, polysaccharides) and to cell-surface receptors, thereby cross-linking matrix components to the cell membrane. Example: Laminin, a major component fo the basal lamina.
Also known as a multiadhesive matrix protein. - What are microfilaments? What is an alternate name. Give at least three functions.
-
Cytoskeletal fiber (~7 nm in dia) that is formed by polymerization of monomeric globular (G) actin;
Also call actin filament.
Microfilaments play an important role in muscle contraction, cytokinesis, cell movement, and other cellular functions and structures. - What is a motor protein? Name two common examples.
-
Any member of a special class of mechanochemical enzymes that use energy from ATP hydrolysis to generate either linear or rotary motion.
Kinesins and dyneins. - What is a myosin head domain?
- Have ATPase activity and in conjunction with the neck domain couple ATP hydrolysis to movement of a myosin molecule along an actin filament via a common mechanism involving cyclical binding and hydrolysis of ATP and attachment/detachment of myosin and actin.
- What is the myosin tail domain?
- Bind the plasma membrane or the membranes of intracellular organelles; as a result, these molecules have membrane-related activities.
- What is a myosin LC kinase?
- Its activation results in the phosphorylation of the myosin regulatory light chain (LC) found in smooth muscle.
- What are plakins?
- An intermediate filament-associated protein (IFAP) that links IFs with microtubules and microfilaments.
- What is a sacromere?
- Repeating structural unit of striated (skeletal) muscle composed of organized, overlapping thin (actin) filaments and thick (myosin) filaments and extedning from one Z disk to an adjacent one. It shortens during muscle contraction.
- What is a sliding-filament assay?
- The movement of fluorescence-labeled actin filaments along a bed of myosin molecules is observed in a fluorescence microscope.
- What are thick filaments?
- Are about 15 nm in diameter and made of several hundred myosin molecules. A thick filament may be likened to a bundle of 200 to 500 "golf club" heads.
- What is a thin filament?
- 7 nm in diameter, are composed primarily of two intertwined strands of F-actin which is made up of subunits of G-actin. Each G-actin site has an active site that can bind to the head of a myosin molecule.
- What is thymosin beta4?
- A G-actin sequestering protein found in a cell.
- What is treadmilling?
- The relative movement of a G-actin molecule from one end of an F-actin fiber to the other. As G-actin is added to (+) end of a microfilament and it is removed from the (-) end, any given G-actin molecule in the filament will move closer to the (-) end.