You have recently been hired by a research team that studies cystic fibrosis (CF), a fatal disorder that clogs the lungs and other organs with a viscous, sticky mucous that interferes with breathing and digestion. The leader of your research team has informed you that a major fraction of the mucous in CF patients consists of filamentous actin (F-actin). His hypothesis is that this actin may play a key role in interfering with breathing and digestion in CF patients. In order to test your laboratory skills and knowledge he decides to give you a quiz.

Your first assignment is to assemble actin monomers into filaments. In a test tube you mix actin monomers (G-actin) with KCl, MgCl2, and ATP and then measure filament assembly with the following result:

You immediately notice that there is a lag phase before actin filaments can be detected and that the ?%actin in filaments? plateaus at less than 100%.

1. Explain the lag phase.

2. Explain why the percent of actin in filaments peaks at a value less than 100%

Your boss then instructs you to try a new experiment. He has you mix actin monomers, KCl, MgCl ₂ , and ATP with short fragments of actin filaments. Your assembly curve looks like this:

3. Why is this curve different from the previous one?

Your boss then suggests that one proposed way to treat CF patients is to reduce the viscosity of the mucous by decreasing the amount of F-actin. He brings three jars from the freezer, labeled ?cofilin?, ?cytochalasin D?, and ?profilin?.

4. Identify which of the three proteins would likely make the mucous even worse and explain why?

Transcribed Image Text:

DI 1001 % actin in filaments time % actin monomers 100 % actin in filaments Time DI 1001 % actin in filaments time % actin monomers 100 % actin in filaments Time

Answer rating: 100% (QA)

1 Actin filaments assembly begins when three actin monomers interact in a certain geometry a process ... View the full answer