POGIL Biology I – Introduction to life on earth
POGIL Biology – Movement across biological membranes
The cell maintains a very precise balance of ions and organic molecules. To accomplish this, it is constantly transporting atoms and molecules across cellular membranes. This exercise explores our current model of the cell membrane and the ways that atoms and molecules can cross biological membranes. Today you will explore some of our conceptual models of these processes.
Model 1 – The fluid mosaic model of biological membranes
[pic]
Model 2 –Transport of molecules across membranes – Facilitated Diffusion
[pic]
Model 3 – Transport of molecules across membranes – Active Transport
[pic]
Using the diagrams above, your textbook, and your note set, answer the following questions.
1. Describe the following symbols in Model 1: spheres with two short tails, coiled ‘strings, ovoid structures attached to coiled strings, small peanut-shaped molecules with tail, tiny polymeric spheres attached to coiled strings.
2. In model 1, where do you see a glycolipid (label it on your diagram)?
3. Draw and label a phospholipid, pointing out hydrophobic and hydrophilic regions of the molecule
4. Model 1 shows proteins embedded in a phospholipid bilayer – why is it referred to as a bi-layer?
5. In the diagram for model 1, point out where on an integral membrane protein you would expect to find polar amino acids. How about non-polar amino acids? Explain your reasoning
6. Biological membranes are selective barriers that allow only some molecules to pass. Why does a cell want to be selective about the molecules it allows in and out?
7. Define the terms diffusion and osmosis.
8. Model 2 illustrates a process termed facilitated diffusion using glucose as an example. Which structure in this model is a channel protein? Describe the five steps in this process.
9. In model 2, is the glucose concentration higher on the inside or the outside of the cell?
10. Is facilitated diffusion active or passive transport? Explain your reasoning.
11. Model 3 shows an example of active transport used by the cell. What is the energy source in this example?
12. In model 3, which ion is pumped out of the cell and which is pumped into the cell? Does this occur sequentially or simultaneously?
13. Is the sodium potassium pump a symporter or antiporter? Explain your answer.
14. Would you expect the Na-K pump to work if there were more sodium ions outside the cell than inside? Why or why not?
15. Under the right conditions, cells from two different organisms can be forced to fuse with each other to form a larger cell (this is analogous to vesicle fusion that occurs in the Golgi). We also know how to label proteins with fluorescent tags, such that cells with labeled proteins ‘glow’ when exposed to light of a specific wavelength. How might you use these techniques to provide evidence that proteins ‘float freely’ in lipid bi-layers?
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