Renewable Energy

Appendix

Instructions for Building a Thylakoid Membrane Model

Materials:

36" X 12" X 2" Styrofoam sheets—5

¼" X ½" X 36" balsa wood strips—7

rubber bands

Toothpicks, wooden skewers and Styrofoam glue are used to connect Styrofoam pieces together.

The Styrofoam lipid bilayer. (See Figure 5.)

• Cut 3 of the 36" sheets in half, creating 6, 18" sections that will form the granum of the model.
• Cut two 4" sections and two 1" sections from a big sheet for the spacer sections of the granum.
• Attach the 4" and 1" spacer pieces to the 18" layers as shown in the diagram using toothpicks and glue.
• To insert the balsa wood support strips, first mark the corners where they will be inserted 1" in from both sides. You can push the strips through the foam quite easily. Use a balsa strip to make all the holes before assembling all the layers of the granum. You can then start from the bottom and add each layer to the balsa supports. Tie or wrap rubber bands around the balsa supports just below the layers so that they will not slip down. Trim off excess wood at the top as necessary.
• For the side pieces (lamellar membranes), cut four 8" sections from one large sheet of foam. Cut angled ends on these to attach to the main unit. Cut four 6" pieces to form the horizontal sections of the lamellar membranes.
• Attach the angled pieces to the 6" pieces with glue and wooden skewers. Taping these while the glue dries may help ensure a good connection.
• For the higher lamella membrane on the left, cut two balsa wood strips approximately 26" long and push these through the two 6" foam pieces at the corners to provide supports as shown in Figure 1.
• For the lower lamellar membrane on the right, cut two balsa strips approximately 16" long and push through the corners of the horizontal 6" side pieces as you did for the left side.
• Attach the angled side pieces to the granum as shown in Figure 1, using glue and wooden skewers. Use tape to hold the foam steady as the glue dries. Wrap and tie rubber bands around the balsa supports to keep the foam from slipping down.
• With a permanent black pen, draw the lipid bilayer onto the foam edges. Where only the phospholipid heads would be showing—the surface of the membrane—attach bubble wrap to make it look like the heads.

Figure 5 — Construction details for the membrane of the thylakoid model

The Photosystems (See Figure 6.)—You will need as many of the parts described here as necessary for the number of photosystems you plan to put on your model. If there is something you can't find, make substitutions that make sense for what the structure or molecule has to do.

1. The reaction centers are made using green 3" X 1" Styrofoam disks. For a reaction center on the edge, cut one disk into quarters. Attach these four quarters to the membrane with glue and toothpicks so that they form two half disks stacked on top of each other. (The reason they were cut into quarters is so the vertical split created will be the boundary of the two dimer units of the reaction center.)

2. Cut another disk in half. Place the two halves back together on the surface of the foam membrane so that the reaction center appears to extend either above or below the membrane. Be sure to note the differences in the position of PS I and PS II in the membrane and in the grana/lamellae.

3. On the flush surface of the membrane, glue a thin layer from a disk, to show the position within the membrane.

4. To show the parts of the reaction centers that extend past the membrane in the middle of the model, just glue down a disk that has been cut in half to show the dimer sections. Add any parts such as the OEC that would be part of that section. Cut small sections of the "antenna" curlers and glue/toothpick around the reaction center. They should be in a circle around PS I and in clusters around PS II.

5. The following is a list of PS and membrane components and the appropriate colors. Refer to Figure 6 for placement. Glue and toothpick will hold most items onto the model. (Half a Styrofoam ball is referred to as a hemisphere.)

1. Q _A—3/4" purple hemisphere
2. Q _B—3/4" yellow-orange hemisphere
3. Phe—green golf tee
4. P680—1 ½" bright green hemisphere
5. Tyr _z—brass thumbtack
6. Cytb ₆f—1 ½" red orange ball
7. P700—1 ½" blue-green hemisphere
8. Fe-S—hot pink golf tee
9. Antenna pigments—2 ½" X ½" curlers painted green, yellow-green and yellow.
10. NADP+ reductase—3" X 1" white Styrofoam disk, notched as shown in Figure 6.
11. ATP Synthase—a 1 ½" pool "noodle", split and hollowed out, connected to a 3" Styrofoam hemisphere, hollowed out, and containing a paper paddle wheel on a wire axle. (See Figure 6)
12. Mn part of OEC—four ½" pale yellow balls held together with toothpicks
13. OEC—1 ½" white sphere with a ¾" wedge cut out.
14. The following are mobile and are not permanently attached:
15. Hydrogen ions—1/2" white Styrofoam balls
16. Water molecule—two hydrogens as above connected by toothpicks to a 1 ¼" ball for oxygen, along with 2 electrons*
17. PQ—1 ¾" black pompom
18. PC—1 ¾" blue pompom
19. Fd—1 ¾" red pompom
20. Electrons*—1/2" silver tipped white pompoms
21. NADP+—two 1 ½" interconnected K'nex standard blue connectors

6. Attach Velcro with strong glue to any parts where there are binding sites, where electrons will be carried, etc.

7. Label parts of the model as needed.

Figure 6 — Construction details for the thylakoid components

Figure 7-Completed thylakoid model.

The ATP Gun Demonstration

(This is not an activity I created. The idea was passed down to me—as so many things are—by other teachers who discovered it, so I do not know who originally created it. My thanks to the person who did; it is one of my favorite analogies. I describe it here as I use it in my classroom.)

Adenosine triphosphate (ATP) has been described as the energy currency of the cell. It is composed of an adenine molecule, a ribose sugar and three phosphate groups. The three phosphate groups are held together by unstable bonds that break easily and release a lot of energy. Energy is transferred from ATP to another molecule when the bond holding the third phosphate group is broken by hydrolysis and the third phosphate group is temporarily transferred to the molecule. At some point, the inorganic phosphate group is released. The remaining molecule with two phosphate groups is called adenosine diphosphate (ADP). ATP can be regenerated by combining ADP with and inorganic phosphate during respiration.

I use a toy dart gun as the ATP molecule. Dollar stores are the best places to find them. Ideally, the gun must be the kind that is spring loaded and shoots a sucker tipped dart. (I do not let students handle the gun, because the type that works best fires the dart with a lot of force and is meant for shooting at targets, not people.) Label the handle of the gun "Adenine", the upper part of the gun "Ribose" and on the barrel draw two phosphate groups. The third phosphate group will be represented by the dart. Label the sucker end of the dart with a "P".

To demonstrate how energy is transferred by ATP, I show the class the loaded "ATP gun". Just slight pressure on the trigger, and the dart is released with a lot of energy. I usually point it at something that I know the dart will stick to—an open cabinet door works well. This shows how the bond is easily broken, but releases a lot of energy. The energy is transferred with the dart, or third phosphate group. When the dart hits the cabinet door, it will move, or even shut, showing the transfer of the energy from the "ATP gun" to another "molecule". Eventually the dart falls off the target, showing also that the phosphate group does not remain on the molecule. I can use it over again—just like real phosphate groups are used over again. The gun is also no longer ATP, but ADP, because it now has only two phosphates. I can make ATP again by recombining the dart with the gun. But if I just place the dart into the gun, it does not stay in place very well and will not fire. I have to push the dart in with considerable force to create the "bond", just as energy must be used to regenerate ATP. I pull the gun out several times during the year when cellular energy topics come up.