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Unformatted text preview: Part 1 Membrane Segment Diagram Refer to figure 7.7 for the model as well as 7.9 for functions of membrane proteins Part 2: Discussion Questions Q1. Regarding membrane fluidity, why is cholesterol considered a "temperature buffer"? At lower temperatures, the movement of phospholipids and membrane proteins slows. Cholesterol prevents the hydrocarbon tails of the phospholipids from tightly associating (packing together) to the point they could solidify. As result, the membrane remains fluid at lower temperatures; phospholipids and membrane proteins can still move. At higher temperatures, the movement of phospholipids and membrane proteins increases. Cholesterol impedes the lateral movement of phospholipids reducing membrane fluidity. Q2. Fill in the table: (From Lecture 3 slides and reading) The form of transport used to What is required for its move it across the plasma transport? membrane and into the cell. Why? (ATP, particular protein,etc) Carbon Dioxide Diffusion: Carbon Dioxide is a small, non-nonpolar molecule The same is true for Oxygen. For animal cells: Oxygen will enter the cell to be used in cellular respiration while carbon dioxide will be excreted by the cell as it is a waste product Osmosis: Facilitated Diffusion Water is a small polar molecule with partial charges (you will learn about this later). Although it has some ability to cross the membrane via diffusion, the amount of water that does this is insignificant compared to the amount of water that passes through transmembrane aquaporin channels. In diffusion molecules move down their concentration gradient: from high to low. Water (pages 133-134) Aquaporins: transmembrane channels Sucrose Active transport, more specifically (pages 137 138) it is an example of cotransport The cotransporter couples the passive diffusion of a H+ ion down its gradient with the active transport of Sucrose against its gradient Na+ Pump: Fig 7.16 Channel: Mentioned in lecture will be discussed more later on. A sucrose cotransporter. H+ ion The cotransporter does not directly use ATP. The cotransporter is functionally linked, but separate from, proton pumps that use ATP to maintain a high concentration of H+ outside of the cell. This maintains the H+ gradient that the cotransporter uses to energize the movement of sucrose. Active transport if moving it out Sodium potassium pump and of the cell. There is much more ATP sodium outside of a cell relative to inside. For this reason active transport is required. Facilitated diffusion if moving Gated ion channel a channel into the cell. Sodium is a small that once activated by either a charged ion, so it does not diffuse ligand (ex: neurotransmitter) or across the membrane efficiently. by depolarization (increase in It requires a transmembrane voltage) allows sodium to rush protein for access. down its concentration gradient. Q3. Past Exam Question: In a blood sample from Peter the Anteater you found that the extracellular concentration of Na+ was 140 mM and the red blood cell volume was 60 m3. The red blood cells were put in 3 different solutions (A, B and C) and the volume of the red blood cells in each solution is shown on the graph below. Indicate whether solutions A, B and C are hypertonic, hypotonic, or isotonic compared to Peter's extracellular fluid. A__Hypotonic__________________ B__ Hypotonic_________________ C____Isotonic_________________________ First, you should look at the graph. The graph depicts the volume of the red blood cells after being placed in solutions A, B, and C. In A, the cells have a volume of 100um3. In B, they have a volume of 80um3. In C they have a volume of 60um3. The graph shows that the volume of the red blood cells in solution C is 60 m3, the same as if the blood cells were in Peter's blood. Therefore solution in C must be isotonic with Peter's blood since cell volume is the same. However the volume of the red blood cells in solution A and B is larger than they were in Peter's blood, so the solution must be hypotonic compared to Peter's blood causing water to flow into the cells. Increased water flow into the cells would cause the cells to swell and increase in volume. ...
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This note was uploaded on 11/22/2010 for the course BIOLOGY SC Bio Sci 93 taught by Professor Dr.dianeo'dowdanddr.rahulwarrior during the Fall '10 term at UC Irvine.
- Fall '10