(A) NO ADDED PROTEIN 8. You have two proteins that you suspect cap the ends of a
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(A) NO ADDED PROTEIN 8. You have two proteins that you suspect cap the ends of actin that end. To determine which protein caps which end, you mix free actin monomers at varying concentrations filaments, preventing actin monomers from either adding or leaving at filament an excess of ATP monomer - either Protein 1, Protein 2, or neither (control) then let the mixture come to steady state. At that point, you measure the mass of free actin monomers and assembled actin microfilaments in the mixture. The plots on the right summarize the results 0.2 0.4 0.6 0.8 actin concentration () (B) PROTEIN 1 A. (4pts) From this evidence, please draw a conclusion as to whether Proteins 1 and 2 cap the plus and/or minus ends of actin microfilaments filament Protein 1 caps which end(s)? - 0 0.2 0.4 0.6 0.8 actin concentration (HM) C) PROTEIN 2 Protein 2 caps which end(s)? - B. (8pts) Please provide the reasoning for your conclusion filament 0 0.2 0.4 0.6 0.8 actin concentration (uM) Figure 16-13 MBoC6 The Problems Book (O Garland Science 2015) Extra credit C. (2pts) With ATP added, the actin microfilaments can undergo treadmilling. Suppose you run the experiments a second time WITHOUT any added ATP. What would you expect when you compare the resulting plots with no added protein, Protein 1 added, or Protein 2 added? Please provide your reasoningExplanation / Answer
Actin filament as two ends marked positive and negative. Positive end observes polymerizations 5-10 times faster. So the reaction goes like filament + actin monomers + ATP = Filament + Actin + ADP.
As we can see that graph for Protein 1 polymerizations kicks off at a lower concentration ( since filament mass is increasing and monomer mass has been stabilized, meaning it is being added to the filament) So we assume that (-) end has been capped prevening disassembly from there while the positive end is adding to, vigorously, While Protein 2 caps the (+) end as filament growth is deterred heavily
C) Actin treadmilling is a phenomenon when monomers are added on the positive side but removed from the negative side maintaining the same filament mass. Hence we could expect the filament mass to go constant whereas monomer mass will increase as we increase the actin concentration because actin monomers will not be used effectively (as it will be added and removed at the same rate).
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