membrane structure and function · 2018. 11. 27. · membrane structure b1yvm 9" teacher resources...

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Membrane Structure B1YvM

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Membrane Structure and Function How do substances move in and out of cells?

Why?

Model 1: Simple Diffusion

1. How many different types of molecules are there in model 1?

2. What are their shapes?

3. Which molecule is larger?

4. In which direction do the molecules move?

5. Which molecules are able to pass through the semi-permeable membrane? Justify your answer.

Everywhere you turn you can’t get away from sports drinks such as Gatorade, Powerade, Vitamin Water etc. All of these drinks are supposed to help your body recover and replenish lost electrolytes, fluids and vitamins after exercise. But how do the essential molecules contained in these drinks get into your cells quickly to help you recover after exercise?

Semi-permeable membrane




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6. If you left this “system” for an extended period of time, would you expect there to be any changes in the concentrations of the molecules on either side of the membrane? Justify your answer.

Model 2: The Fluid Mosaic Model

7. How many types of protein molecules are found in the model?

8. What is the difference between the surface proteins and the membrane spanning proteins?

9. What are the two major types of biological molecules that compose the fluid mosaic model?

10. When a carbohydrate chain is attached to a protein what is the structure called?




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11. When a carbohydrate is attached to a phospholipid what is the structure called?

12. What types of molecules appear to be moving across the membrane?

13. With your group list as many examples as you can of small polar and small non-polar molecules that may be involved in moving across cell membranes.

14. Where exactly in the membrane do these molecules pass through?

15. How does the concentration of the small molecules inside the cell compare to that outside the cell?

16. Because of the random movement of molecules they tend to move across the membrane in both directions. Do the molecules appear to move equally in both directions? Justify your answer using complete sentences.

17. Using all the information from the previous questions complete the passage below: Diffusion is the movement of molecules from an area of ____________ concentration to an area of _________ concentration. The molecules will continue to move along this concentration gradient until they reach equilibrium. In cells, small _____________ molecules, such as water and small ____ - ________ molecules such as ______ and ___________ move by _____________ across the cell membrane.




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Model 3: Facilitated Diffusion

18. Which part of the cell membrane is shown in more detail in Model 3?

19. What is the gap between the proteins called?

20. What type of molecules attach to the protein?

21. Looking at the diagram on the left, will the glucose molecules be able to pass

through the protein channel? Explain your answer in complete sentences.

22. Explain in detail what has happened in the diagram on the right that has allowed the glucose molecules to pass through.

Area shown in more detail Area shown in more detail




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23. Discuss with your group why this type of protein channel is called a gated channel. Write your group’s responses below

24. To facilitate means to help. Why is this type of diffusion called facilitated diffusion?

25. Facilitated diffusion is also the way that ions such as Na+ and K+ cross the membrane. Why would these molecules not cross by (simple) diffusion?

Model 4: Active Transport

26. Which part of the cell membrane is shown in more detail in Model 4?




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27. What are the two binding sites found on the protein?

28. What is ATP?

29. What is different about an ion compared to the other molecules that have moved

across the membranes by diffusion and facilitated diffusion?

30. Once the ion and ATP bind to their respective sites, what happens to the protein channel?

31. What happens to the ATP once it binds to the protein?

32. Does this change in ATP transfer energy to or from the protein channel?

33. Are the ions being moved FROM an area of high concentration or low concentration?

34. Are the ions moving TO an area of high concentration or an area of low concentration?

35. Using your answers to the previous two questions, summarize the movement of particles in Model 4.

36. Are the ions being moved along (down) a concentration gradient? Justify your answer.




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37. This type of transport is called Active Transport, while diffusion and facilitated diffusion are called Passive Transport. With your group complete the table below to show the difference between active and passive transport:

Active Transport Passive Transport Diffusion Facilitated

Diffusion Requires energy input by the cell

Moves molecules along a concentration gradient

Always involves channel (membrane-spanning)proteins

Moves charged ions Moves large molecules Moves small non polar/ molecules

Moves molecules against the concentration gradient

Molecules pass between the phospholipids

38. With your group develop a definition for active transport.




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Extension Questions:

39. Using your knowledge of mechanisms of transport across membranes, suggest why the rate of diffusion shows a linear trend as concentration difference increases, whereas the rate for facilitated diffusion eventually reaches a maximum.

40. Why does active transport, on the same graph, start off with such a high initial rate compared to diffusion and facilitated diffusion?




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Teacher Resources

Learning Objectives:

1. Students will be able to identify the two main molecule types in a model of the lipid bi-layer and state the essential function of each.

2. Students will be able to distinguish between passive and active transport and give examples and definitions of types of passive transport, including diffusion and facilitated diffusion.

3. Students will be able to predict the direction of movement and mechanism for common molecules such as O2, CO2, glucose, and charged ions (K

+, Na+, Ca2+).

Prerequisites:

1. Students should already have an understanding of biological molecules and their structures.

2. Student should have a basic understanding of polar/non-polar molecules and the properties of water.

Assessment Questions:

1. List three ways that substances can pass across a membrane, and for each one state whether it is active or passive. Diffusion & facilitated diffusion (passive); Active transport (active)

2. What are two differences between active transport and diffusion? Active transport

moves molecules against a concentration gradient; diffusion moves molecules along a concentration gradient. Active transport uses energy; Diffusion does not. Active transport uses carrier proteins; diffusion does not.

3. Structure A is:

a. Glycoprote in b. Glycolipid c. Phospholipid d. Protein

A




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Teacher Tips:

• Term equilibrium is introduced/used at the end of Model 1. If your students have not come across this term before you may need to stop and clarify at this point.

• The extension questions may require additional help so that students understand the concept of rate.

Target Responses

1. How many different types of molecules are there in model 1? Two

2. What are their shapes? Circ le & tr iangle

3. Which molecule is larger? Triangle

4. In which direction do the molecules move? Both direc t ions

5. Which molecules are able to pass through the semi-permeable membrane? Justify your answer. The c ir c l es . Because they are smal l and can f i t though the gaps , and because they are equal ly dis tr ibuted on both s ides o f the membrane .

6. If you left this “system” for an extended period of time, would you expect there to be any changes in the concentrations of the molecules on either side of the membrane? Justify your answer. No, the concentrat ion o f tr iangles wi l l remain high on the l e f t and none on the r ight as they can’t f i t through the membrane, and the c i r c l es wi l l s tay evenly balanced due to random movement .

7. How many types of protein molecules are found in the model? Four – 2 types o f sur face prote in and 2 types o f membrane spanning.

8. What is the difference between the surface proteins and the membrane spanning proteins? The sur face just s i t on e i ther the ins ide or outs ide sur face , wheras the membrane spanning pass r ight through the phosphol ipids .

9. What are the two major types of biological molecules that compose the fluid mosaic model? [Phospho] l ip ids and prote ins .

10. When a carbohydrate chain is attached to a protein what is the structure called? Glycoprotein




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11. When a carbohydrate is attached to a phospholipid what is the structure called? A glyco l ipid .

12. What types of molecules appear to be moving across the membrane? Small non-polar or polar molecules .

13. With your group list as many examples as you can of small polar and small non-polar molecules that may be involved in moving across cell membranes. Small non-polar : O2; CO2. polar : water .

14. Where exactly in the membrane do these molecules pass through? Between the phosphol ipids .

15. How does the concentration of the small molecules inside the cell compare to that outside the cell? There are more smal l molecules outs ide the ce l l compared to ins ide , so the concentrat ion is higher outs ide compared to ins ide .

16. Because of the random movement of molecules they tend to move across the membrane in both directions. Do the molecules appear to move equally in both directions? Justify your answer using complete sentences. No, more molecules are moving into the ce l l compared to moving out o f the ce l l . The arrows show the movement .

17. Using all the information from the previous questions complete the passage below: Diffusion is the movement of molecules from an area of HIGH concentration to an area of LOWER concentration. The molecules will continue to move along this concentration gradient until they reach equilibrium. In cells, small POLAR molecules, such as water and small NON - POLAR molecules such as O2 and CO2 move by DIFFUSION across the cell membrane.

18. Which part of the cell membrane is shown in more detail in Model 3? The membrane spanning prote in.

19. What is the gap between the proteins called? A gated channel

20. What type of molecules attach to the protein? Hormones




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21. Looking at the diagram on the left, will the glucose molecules be able to pass through the protein channel? Explain your answer in complete sentences. No because they are too large to f i t through the narrow gap in the gated channel .

22. Explain in detail what has happened in the diagram on the right that has allowed the glucose molecules to pass through. The hormone at tached to the prote in and caused i t to change shape. This made the channel larger and al lowed the g lucose to pass through .

23. Discuss with your group why this type of protein channel is called a gated channel. Write your group’s responses below Because i t ac ts l ike a gate . When the hormone molecule binds i t i s l ike a key that opens the locked gate and al lows molecules through.

24. To facilitate means to help. Why is this type of diffusion called facilitated diffusion? Because i t i s s t i l l d i f fus ion o f molecules but i t needs the he lp o f another molecule to open the prote in channel .

25. Facilitated diffusion is also the way that ions such as Na+ and K+ cross the membrane. Why would these molecules not cross by (simple) diffusion? Because they are charged part i c l es , and so cannot move between the phosphol ipids to cross the membrane without a channel .

26. Which part of the cell membrane is shown in more detail in Model 4? The membrane spanning prote in

27. What are the two binding sites found on the protein? Ion binding s i t e and ATP binding s i t e .

28. What is ATP? Energy molecule

29. What is different about an ion compared to the other molecules that have moved across the membranes by diffusion and facilitated diffusion? Ions are charged part i c l es .

30. Once the ion and ATP bind to their respective sites, what happens to the protein channel? It opens up to l e t the ion through.

31. What happens to the ATP once it binds to the protein? It changes to ADP .




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32. Does this change in ATP transfer energy to or from the protein channel? Breakdown of ATP to ADP transfers energy to the channel .

33. Are the ions being moved from an area of high concentration or low concentration? Low concentrat ion

34. Are the ions moving to an area of high concentration or an area of low concentration? High concentrat ion

35. Using your answers to the previous two questions, summarize the movement of particles in Model 4. The part i c l es move from an area o f low concentrat ion to an area o f high concentrat ion

36. Are the ions being moved along a concentration gradient? Justify your answer. No, as there i s a lready a higher concentrat ion o f ions on the opposi t e s ide o f the membrane.

37. This type of transport is called Active Transport, while diffusion and facilitated diffusion are called Passive Transport. With your group complete the table below to show the difference between active and passive transport:

Active Transport Passive Transport Diffusion Facilitated Diffusion

Requires energy input by the cell

yes no no

Moves molecules along a concentration gradient

no yes yes

Always involves channel proteins

yes no yes

Moves charged ions yes no yes Moves large molecules yes no yes Moves small non polar/polar molecules

no yes no

Moves molecules against the concentration gradient

yes no no

Molecules pass between the phospholipids

no yes no




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38. With your group develop a definition for active transport. Active transport i s the movement o f molecules against a concentrat ion gradient requir ing the use o f energy and membrane-spanning prote ins.

39. Using your knowledge of mechanisms of transport across membranes, suggest why the rate of diffusion shows a linear trend as concentration difference increases, whereas the rate for facilitated diffusion eventually reaches a maximum. This i s due to the rate be ing l imited by the number o f transport prote ins avai lable in the l ip id bi - layer . Despi te the change in concentrat ion the number o f prote in channels wi l l l imit the rate o f fac i l i tated di f fus ion.

40. Why does active transport, on the same graph, start off with such a high initial rate compared to diffusion and facilitated diffusion? Active transport does not depend on a concentrat ion gradient , only a supply o f energy .

membrane structure and function · 2018. 11. 27. · membrane structure b1yvm 9" teacher resources...

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