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Unformatted text preview: 1 Actin Cytoskeleton Cell Motility Muscle Contraction Intermediate Filaments BIO320 - 2009- Lectures 14 & 15 Cell Motility: Cells move in many ways! Cells change shape and move across a substrate Leukocyte Fibroblasts Keratocytes Microflaments make the Actin Cytoskeleton Microfilaments have two protofilaments G-Actin F-Actin Alberts 16-11 The Assembly of Microtubules and Microfilaments have Several Properties in Common • Filaments have polarity • Use a nucleotide to control assembly/disassembly • Concentration dependent • Require a nucleus Actin flaments are polar due to the specifc & asymmetric interactions between monomers Karp 9-44 (+) end (-) end 2 Polymerization occurs preferentially at the (+) end See Alberts Panel 16-2 (+) end (-) end Actin Flament assembly is ATP dependent CAUTION: Some aspects of Alberts 16-14 are WRONG ¡ilament has higher afFnity for ATP-Actin than for ADP-Actin Hydrolysis of ATP is NOT concurrent with assembly Hydrolysis of ATP is not coupled to polymerization (+) end (-) end ModiFed from Alberts Polymerization is dependent on concentration of G-Actin At steady state: Rate of Growth = Rate of Shrinkage Concentration of monomers at steady state = Cc Polymerization occurs preferentially at the (+) end The Cc at the (+) end is lower than the Cc at the (-) end Cc(+) < Cc(-) old part of Flament (+) end (-) end ModiFed from Alberts 16-14 Polymerization is dependent on concentration of G-Actin Both ends combined What happens if both ends are considered? What happens above Cc(-)?...
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- Spring '09
- O' HALLORAN
- cell biology