细胞科学 Science 蔡国
细胞科学 Cell Science （10.2） 蔡国平
10.2 Structure and composition of microfilament They are solid, thinner filament structures(6-8 nm, in diameter) composed of a double-helical polymer of the protein actin. And microfilaments play a key role of in virtually all types of contractility and location of cells as well as motility within cells L. Actin The most abundant protein in many eukaryocytic cells of constituting 5 or more of the total cell proteins(20% of their mass is actin in muscle cell). A typical cytosolic concentration of actin in nonmuscle cells is 0. 5mM Actin has MW 42KD with x 375 amino acid residues encoded by a large, highly conserved gene family. Some single-celled enkaryotes, e.g. yeasts and amebas have only a single actin gene, whereas many eukaryotes contain multple actin genes
10.2 Structure and composition of microfilament They are solid, thinner filament structures (6-8 nm, in diameter) composed of a double-helical polymer of the protein actin. And microfilaments play a key role of in virtually all types of contractility and location of cells as well as motility within cells. 1. Actin The most abundant protein in many eukaryocytic cells, of constituting 5 % or more of the total cell proteins (20% of their mass is actin in muscle cell). A typical cytosolic concentration of actin in nonmuscle cells is 0.5mM. Actin has MW 42KD with ~ 375 amino acid residues, encoded by a large, highly conserved gene family. Some single-celled enkaryotes, e.g. yeasts and amebas have only a single actin gene, whereas many eukaryotes contain multple actin genes
In vertebrate, there are three isoforms, a,B, y actin, together form a closely related family whose members are specialised for different types of motile processes. The structure of actin has been remarkably conserved throughout the couse of evolution (it is 88% identical between yeast/ rabbit muscle). The four a-actin isoforms present in varios muscle cells and the B-and y-actin isoform present in nonmuscle cells differ at only 4 to 5 positions. The a-actin is associated with contractile structure, B-actin is at the front of the cell, forming filaments. Actin filaments consist of one or two isoforms in skeletal cells. consist of a-actin. while in smooth muscle cell consist of a-actin and y-actin; in nonmuscle cells, consist of the B-and y-actin
In vertebrate, there are three isoforms, actin, together form a closely related family whose members are specialised for different types of motile processes. The structure of actin has been remarkably conserved throughout the couse of evolution (it is 88% identical between yeast/ rabbit muscle). The four -actin isoforms present in varios muscle cells and the - and -actin isoform present in nonmuscle cells differ at only 4 to 5 positions. The -actin is associated with contractile structure; -actin is at the front of the cell, forming filaments. Actin filaments consist of one or two isoforms, in skeletal cells, consist of -actin, while in smooth muscle cell consist of -actin and -actin; in nonmuscle cells, consist of the - and -actin
Figure 22-15 The Molecular Structure of G-Actin Monomer X-ray crystallography shows that the G-actin monomer is shaped somewhat like a U A nucleotide (ATP or ADP) binds reversibly in a groove in the protein. When G-actin monomers polymerize into F-actin, the mouth of the groove is covered by another G-actin monomer, trapping the bound nucleotide inside. In addition, binding of one G-actin to another forces the mouth of the groove to close more tightly on the bound nucleotide, promoting hydrolysis of the ATP
Fis gure 11.2 Assembly and structure of actin fila ments (A)Actin monomers(G actin) polymerize to form actin filaments (F actin). The first slep is the formation of dimers and trimers, which then grow by the addition of monomers to both ends.(B)Structure of an actin monomer(C")Space-filling model of F actin. Nine actin monomers an rpr nted in different colors. (O Dan Richardson
actin molecule Figure 16-25 Actin filaments. (A) Electron micrographs of negatively stained actin fil minus end minus end aments. (B)Arrangement of actin mole cules in an actin filament, Each filament may be thought of as a two-stranded helix with a twist repeating every 37 nm. Strong interactions between the two strands pre vent the strands from separating, (C)The identical subunits of an actin filament are depicted in different colors to emphasize the close interaction between each actin molecule and its four nearest neighbors (A, courtesy of Roger Craig: C, from K.C. Holmes et al. Nature 347: 44-49, 1990, copyright Macmillan Magazines Ltd 37 nm plus end 50 nm
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