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B1105 HWK 4_STDT (1) - BIOL 1105 Homework 4

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BIOL 1105Homework 4Instructor: SeshanName: _____________________________Section (circle one)9:25 am10:50 amDue:Friday October 21 at 12 pmWSC 209Instructions:These questions are based on lecture material but may require additional research usingyour textbook or other outside resources.1. Imagine a unicellular organism from another planet, which has a cytoplasm and a plasma membrane.The cytoplasm is similar in composition to the aqueous cytoplasm of Earthly organisms. However, it livesin a lake-­‐like environment that is oily instead of containing water (i.e. aqueous). [Total 11 pts]1a. Using this information, draw the plasma membrane of this organism and explain how the lipidswould be arranged. [7 pts]1b. Do you think that this plasma membrane would contain proteins with sugar groups facing theexternal (extracellular) face of the plasma membrane? Explain your answer. [4 pts]2. The image below, taken from figure 5.12 of your textbook, illustrates how the Na+-­‐K+pumpnormallyfunctionsin the plasma membrane.Imaginethat you
BIOL 1105Homework 4Instructor: Seshanhave prepared lipid vesicles (spherical lipid bilayers) that contain Na+-­‐K+pumps as the sole membraneprotein. All of the Na+-­‐K+pumps are oriented in such a way that the portion of the molecule thatnormally faces the cytosol is on the inside of the vesicle and the portion of the molecule that normallyfaces the extracellular space is on the outside of the vesicle. Assume that each pump transports one Na+ion in one direction and one K+ion in the other direction during each pumping cycle. [12 pts total; 4 ptseach]After carefully reading the section in your textbook that explains how the Na+-­‐K+pumps function, predictwhat would happen in each of the following conditions:2a. The solutions inside and outside the vesicles contain both Na+and K+ions but no ATP.2b. The solution outside the vesicles contains both Na+and K+ions; the solution inside contains both Na+and K+ions and ATP.2c. The solution outside contains Na+; the solution inside contains Na+and ATP.3. Some cells have aquaporins, which are channels that facilitate the flow of water molecules throughthe plasma membrane. For these cells, what regulates the rate and direction of water diffusion acrossthe membrane? [4 pts]
BIOL 1105

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Term
Fall
Professor
LiliannaBusconi
Tags
molecular biology, pts, Seshan, Mazda Luce

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