Search results
Results from the WOW.Com Content Network
Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin , but are modified by and interact with numerous other proteins in the cell.
Microfilament Polymerization. Microfilament polymerization is divided into three steps. The nucleation step is the first step, and it is the rate limiting and slowest step of the process. Elongation is the next step in this process, and it is the rapid addition of actin monomers at both the plus and minus end of the microfilament.
The oligomerization is the rate-determining step, considering actin filament formation as a whole. The so-called lag phase of actin polymerization originates from this step. It takes quite a while until polymerization starts, but once it has, the process is autocatalytic until the physiological maximum of the polymerization rate is reached.
The protein gelsolin, which is a key regulator in the assembly and disassembly of actin. Other proteins bind to the ends of actin filaments, stabilizing them. These are called "capping proteins" and include CapZ and tropomodulin. CapZ binds the (+) end of a filament, preventing further addition or loss of actin from that end. [121]
Nucleation is the event that initiates the formation of microtubules from the tubulin dimer. Microtubules are typically nucleated and organized by organelles called microtubule-organizing centers (MTOCs). Contained within the MTOC is another type of tubulin, γ-tubulin, which is distinct from the α- and β-subunits of the microtubules themselves.
The latter formation is commonly referred to as a "9+2" arrangement, wherein each doublet is connected to another by the protein dynein. As both flagella and cilia are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton. There are two types of cilia: motile and non-motile cilia.
Cytochalasins are fungal metabolites that have the ability to bind to actin filaments and block polymerization and the elongation of actin. As a result of the inhibition of actin polymerization, cytochalasins can change cellular morphology, inhibit cellular processes such as cell division, and even cause cells to undergo apoptosis. [1]
Within the lamellipodia are ribs of actin called microspikes, which, when they spread beyond the lamellipodium frontier, are called filopodia. [2] The lamellipodium is born of actin nucleation in the plasma membrane of the cell [1] and is the primary area of actin incorporation or microfilament formation of the cell.