(5The nucleation of actin filaments at the PM is frequently regulated by external signals, allowing the cell to change its shape and stiffness rapidly in response to changes in its external environment This nucleation is catalyzed by a complex of proteins that includes two actin-related proteins, or ARPs(Arp2 and arp3). minus ends of actin flaments memhrane-bound actin-nucleating sites iplurs ends of actin laments) microspike substratum close contact wth substratum actin cross-linking proteins A 0.2 urm
(5)The nucleation of actin filaments at the PM is frequently regulated by external signals, allowing the cell to change its shape and stiffness rapidly in response to changes in its external environment. This nucleation is catalyzed by a complex of proteins that includes two actin-related proteins, or ARPs(Arp2 and Arp3)
stress fiber filopodium cell cortex contractile bundle gel-like network tight parallel bundle 100nm Actin arrays in a cell
Actin arrays in a cell
o HI Figure 16-55 Lamellipodia and microspikes at the leading edge of a human fibroblast migrating in culture. The arrow in this scanning electron micrograph shows the direction of cell movement. As the cell moves forward, lamellipodia and microspikes that fail to attach to the tissue culture dish sweep backward over its dorsal surface-a movement known as ruffling.(Courtesy of Julian Heath)
Figure 16-55 Lamellipodia and microspikes at the leading edge of a human fibroblast migrating in culture. The arrow in this scanning electron micrograph shows the direction of cell movement. As the cell moves forward, lamellipodia and microspikes that fail to attach to the tissue culture dish sweep backward over its dorsal surface - a movement known as ruffling. (Courtesy of Julian Heath.)
Specific drugs affect polymer dynamics Cytochalasins: Prevent the addition of new monomers to existing MFS, which eventually depolymerize. Phalloidin: a cyclic peptide from the death cap fungus, blocks the depolymerization of mf Those drugs disrupt the monomer-polymer equilibrium, so are poisonous to cells
C. Specific drugs affect polymer dynamics Cytochalasins: Prevent the addition of new monomers to existing MFs, which eventually depolymerize. Phalloidin: A cyclic peptide from the death cap fungus, blocks the depolymerization of MF Those drugs disrupt the monomer-polymer equilibrium, so are poisonous to cells
H2l CH2 H3C-CH CHOH H CH HC (A) leading edge of cell (B H n3 cytochalasin B Figure 16-52 The effect of cytochalasin on the leading edge of the growth cone of a nerve cell in culture. A living growth cone is viewed by nomarski differential-interference-contrast microscopy both before(A) and after(B)treatment with cytochalasin. The cell in (B)has then been stained with rhodamine phalloidin to reveal the actin filaments(C). Note how the region behind the leading edge of the cytochalasin-treated growth cone is devoid of actin filaments. Cytochalasin B(D).(A, B, and C, courtesy of Paul Forscher
Figure 16-52 The effect of cytochalasin on the leading edge of the growth cone of a nerve cell in culture. A living growth cone is viewed by Nomarski differential-interference-contrast microscopy both before (A) and after (B) treatment with cytochalasin. The cell in (B) has then been stained with rhodamine phalloidin to reveal the actin filaments (C). Note how the region behind the leading edge of the cytochalasin-treated growth cone is devoid of actin filaments. Cytochalasin B (D). (A, B, and C, courtesy of Paul Forscher.)