Lesson 4 GRQs Membrane Structure and Function PDF

Preview

Summary

Lesson 4 GRQ's answers and questions for Biology 101....

Description

Membrane Structure and Function (Guided Reading Questions to do before Mastering Biology)

(Reading Chap 5 Intro-5.9) Reading Objectives  Describe cell membrane structure  Differentiate the kinds of molecules that can freely cross cell membranes vs. those that can’t.  Compare and contrast the different ways in which various substances cross membranes.  Make predictions about water movement during osmosis. Q1. The chapter opener discusses aquaporins. What is the function of these proteins? They function as water channels where water molecules on both sides of the phospholipids membrane slip into a single file along the blue ribbons. What if a person has too many in the membranes of their kidney cells? What if a person has too few in the membranes of their kidney cells?

2. What is meant by the terms “fluid mosaic” and “selective permeability” when describing membranes? “Fluid mosaic” model just represents a diverse protein molecule suspended in a fluid phospholipid bilayer. “Selective permeability” just means that a cell allows some substances to cross more easily than others therefore making it a selective permeability.

3. Why was the spontaneous formation of membranes such an important step in cell evolution? A membrane can enclose a solution that is different in composition from its surrounding. If that solution included self-replicating molecules such as RNA and a beneficial assortment of other molecules, these combinations could be passed on to daughter cells as new membrane-enclosed vesicles budded off.

4. Use the words diffusion and concentration gradient in a sentence. Diffusion is used to reach an equilibrium between a substance and to lower the concentration gradient. 5. How does the structure of the membrane relate to its selective permeability? (Think about the chemical properties of the inner core of the bi-layer.) The membrane needs embedded proteins that could regulate the movement of substances into and out of the cell. What kinds of molecules can freely cross through passive transport without transport proteins? (Review and define the words polar and nonpolar if you need to!) Nonpolar molecules can easily diffuse without the help of transport proteins. 

What kinds of molecules use facilitated diffusion (a kind of passive transport that requires transporter proteins)? Ions and Polar molecules if they are moving down their concentration gradients. 

6. If I give you a 5% sucrose solution and a 10% sucrose solution, in which is the water less concentrated? The water is less concentrated in the 10% sucrose solution 7. When water moves through a selectively permeable membrane down its concentration gradient this is termed osmosis. 8. Is seawater hypertonic, isotonic, or hypotonic to drinking water? Hypertonic 9. If a hypotonic solution is put in a selectively permeable membrane and put into a hypertonic solution, what will happen to the bag over time? (shrink or swell?) Why? Where is the water more concentrated? Overtime, the bag will shrink because there is a higher solute concentration outside of the bag so water will leave the bag. 10. Water is a polar molecule and thus diffuses slowly into cells. What type of membrane protein would you expect to find many of in a cell that must be highly permeable to water? Carrier Protein

11. Scientific Thinking in Module 5.7: Sometimes discovery is accidental. What type of cell did Dr. Agre’s team accidentally discover aquaporins in? Blood cell In their work, shown in Figure 5.7 control frog eggs were compared to frog eggs that carried genetic information to make many aquaporins. What result did they get when they put these two groups of eggs in a hypotonic situation (describe Figure 5.7). The experimental eggs exploded within 3 minutes and the control group stayed relatively fine and did not explode. What did it tell them about the function of aquaporins?

This told them that aquaporins allow only water molecules to pass through them. 12. In our discussion of how cells use glucose as an energy resource, we will see that cells are continually bringing glucose in from the blood where the concentration is higher. What kind of transport does glucose use? Active Transport

10. How do calcium ions move against their concentration gradient? They use active transport which allows a cell to maintain internal concentration of small molecules and ions that are different from concentration in its surroundings. 11. Compare and contrast exocytosis and endocytosis. Both of these process transports a large amount of something but where they differ is in what they are transferring. Exocytosis exports bulky materials such as proteins or polysaccharides and endocytosis transports large molecules or droplets of fluids.

What are the distinctions between phagocytosis and receptor-mediated endocytosis? Phagocytosis engulfs a particle by wrapping extensions called pseudopodia around it and packaging it within a membrane-enclosed sac called a vacuole. Receptor-mediated endocytosis enables a cell to acquire specific solutions....