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Biology Demos
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by Thea Sinclair
St. Stephens High School
Hickory, North Carolina
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| | ATP Energy Jar
Get a large jar with a screw top, such as a mayonnaise or canning jar. Cut two strips of white paper and fit them around the jar. Put a P on both of them. Make a third strip of paper and fit it around the lid. Put another P on that strip. Print the word ENERGY on a strip of paper and tape it so it hangs down the inside of the lid.
After teaching the ATP/ADP cycle, show the students the jar with the lid on it. This jar represents a molecule of ATP. Remove the lid, and show how energy is released when a phosphate is removed. Ask them what molecule remains, and they should say that it is ADP because of the two P s on the jar. When ADP is converted to ATP, a phosphate group is required, and it takes energy to phosphorylate the ATP. Put the lid back on the jar, and show that the energy is now stored in the molecule.
Recombinant DNA
You will need four pieces of ribbon or cloth of two different colors and Velcro self-adhesive strips. You also need a jar or Styrofoam packing that comes with chemicals or nutrient agar to prevent it from breaking. This will represent a bacterium.
The first piece of ribbon will be the bacterial plasmid. Place Velcro at the ends of the ribbon and connect them to form a circle. The second piece of ribbon represents the donor chromosome, for example, a human chromosome containing the gene for insulin. Place two more pieces of Velcro about one-third and two-thirds of the way down the ribbon.
To show the recombination process, cut the chromosome ribbon above and below the two pieces of Velcro. The cuts represent the recognition sites of the restriction enzymes. Open up the plasmid, indicating that the same restriction enzyme will cut it as well. Then connect the cut pieces with the ribbon plasmid. Reconnect the circle and place the plasmid in the bacterial host. Have an identical recombined plasmid in a second host model, and show that every time the bacterium divides, a copy of the desired gene is made as well. (To use the chromosome again, just tape it back together and break it at the tape line.)
DNA Replication
(Adapted from the 10/96 American Biology Teacher article by Malacinski and Zell)
Materials needed can be easily obtained at a crafts store such as Michaels or A. C. Moore
Per Student or Student Pair
- large Ziploc bag
- five pipe cleaners -- red, blue, pink, green, and yellow (cut the green and yellow into four pieces)
- one pink pony bead
- five red pony beads
- one green propeller bead (Pony beads and propeller beads can be bought in small bags.)
- paper hole reinforcements
- self-stick labels or masking tape
Student Directions
1. Twist the two strands of DNA (red and blue pipe cleaners) around each other.
2. Label the red strand 3' and the blue 5' at the top.
3. Label the red strand 5' and the blue 3' at the bottom.
4. Attach two paper hole reinforcement labels with ATP written on them to the pink pony bead. This shows that two ATP molecules are required for unwinding each base pair. Slide the pink pony bead over the twisted strand at the top. This represents the enzyme helicase. As the helicase slides down the double helix, unwind the two strands. You are producing a replication fork.
5. One DNA strand (red) is prevented from reannealing with the complementary DNA strand by the action of ssb proteins. Thread five red pony beads -- representing the DNA binding proteins -- down the red DNA strand, all the way to the fork, butting up against the helicase bead.
6. Leading strand synthesis begins by attaching an RNA primer (green pipe cleaner piece) at the 3' end. Next, wind a pink pipe cleaner representing deoxyribonucleoside triphosphates around the red DNA strand beginning at the RNA primer. On the end of the pink stem that approaches the fork, attach a green propeller-shaped bead to represent DNA polymerase, the enzyme that catalyzes the reaction of new nucleotides along the DNA template.
7. Lagging strand synthesis is more complex. Wrap a green pipe cleaner piece (RNA primer) around the blue DNA strand at the replication fork. Primase and DnaB proteins synthesize the RNA primer. Next, wrap an Okasaki fragment (yellow pipe cleaner) to which DNA polymerase is attached (green propeller bead) around the DNA template, heading in the direction out of the fork. Repeat the addition of another green RNA primer and yellow Okasaki fragment.
In reality, the RNA primers would be removed and replaced with deoxyribonucleotides. The gaps are sealed with the enzyme ligase
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