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final prob set 3-07

final prob set 3-07 - MCB 100B Spring 2007 Problem Set 1 A...

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MCB 100B Spring 2007 Problem Set 1. A colleague studying oxidative phosphorylation uses isolated, functioning mitochondria and continuously washes the intermembrane space with neutral buffer. He demonstrates that this effectively neutralizes the effect that the pumping of protons by the electron transport chain has on the pH of the intermembrane space. The mitochondria continue to produce ATP. Thus he concludes that an alternative mechanism to that described by the chemi- osmotic hypothesis must exist. 2. Bacterial flagellar function is dependent on the energy available from the proton motive force. What is the proton motive force and how is it created? 3. Certain organisms that grow in the absence of oxygen are known to use the proton motive force to power transport and other energy-requiring processes. a. How, in aerobic organisms, is the proton motive force produced? Explain why this mechanism is dependent on the presence of oxygen. b. How could an organism create the pmf in the absence of oxygen? 4. Fluidity has been shown to be a critical characteristic of membranes. Which component of the electron transport chain is embedded in the membrane and must diffuse rapidly through that membrane to function. What feature in the structure of that molecule allows it to be embedded in the membrane. 5. A colleague studying electron transport adds an inhibitor and watches the spectrum of one of the cytochromes. After allowing the inhibitor to take effect, he verifies that electron transport has been halted, but is surprised to discover that his cytochrome has become more fully oxidized rather than reduced. Explain fully. 6. A graduate student wishes to make micelles composed of fatty acids. He plans to get the fatty acids through the hydrolysis of the lipids found in animal cell membranes. He is given the choice of using gangliosides or phosphoglycerides as a source of the fatty acids. a. What is the backbone molecule for each of these types of lipids? Names, not structures required. b. If the student is interested only in getting as many micelles as possible from a given number of molecules of starting material, should he use gangliosides or phosphoglycerides. Explain c. Why can’t he make micelles from the phosphoglycerides or gangliosides themselves. d. What is the fundamental structural difference between a micelle and a cell membrane-- other than the size.
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7. Oligomycin does not interact directly with any component of the electron transport chain yet it causes the ratio of reduced to oxidized coenzyme Q to change significantly. a. Explain. b. What could be added to the system to allow electron transport to restart. Explain. 8. A careless investigator accidentally drops some cyanide into a preparation of isolated mitochondria. Continuing to fumble around, he then drops some very dilute acid into the preparation and goes out to lunch. A colleague examines the preparation, and is surprised to find an apparent contradiction between his measurements of O 2 consumption and ATP production. What is happening and propose an explanation for it.
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