Class 2: The World of BioPolymers
Class Goals:
1)To provide an introduction to natural polymers
2)Examine how proteins and DNA are polymers and what can effect there
Behavior
Organization
Two experiments are two be performed during this class. One tests how the proteins in Jell-O are affected by the protease enzymes in different fruits. The second experiment is to extract DNA strands from a variety of different food products. Since it will take at least one hour for the affects of the fruit on the Jell-O to become apparent, it is recommended that the class be lead off with giving the students individual bowls of Jell-O and a fruit, having them place the fruit on the Jell-O, then waiting at least one hour before making observations. In the meantime, the DNA extraction experiment should be performed.
A) Soup or Salad: Investigating the Action of Enzymes in Fruit on Gelatin
This experiment seeks to show how certain enzymes, called protease, cause the breakdown of proteins, which are polymers, in Jell-O causing the release of water from the protein matrix. Fruits known to contain such enzymes include fresh and frozen pineapple, kiwi, and figs. Canned or cooked fruits will not work since the enzymes are deactivated by increased temperatures. A small PowerPoint presentation is supplied which gives a protein diagram, pictures of Jell-O formation, and a couple points of discussion.
Materials Needed: Jell-O prepared as instructed on the box instructions still chilled, meat tenderizer, frozen-canned-fresh pineapple, kiwi, and any other fruits desired
Procedure
1)The Jell-O should be prepared ahead of time in small, individual bowls or cups so each student can have one.
2)Give each student a piece of fruit. Have the students place the fruit juice side down on the Jell-O. On one additional bowl, sprinkle some meat tenderizer
3)
Wait at least one hour. Have the students make there observations individually in a copy of a chart like the one listed below:
Questions to Consider (The follow is all contained in the PowerPoint slides)
1)What is protease?
-Any Enzyme that breaks the amino acid bonds in proteins
-Pineapples protease called contain bromelain; in Kiwi it is actinidin
-Meat Tenderizers are often made from pineapple stems to get the bromelain
to break down proteins in meats
-Protease Inhibitors used to treat HIV
HIV protease is prevented from breaking down viral proteins that spread
to other cells. If they cannot break down, the virus is slowed dramatically
2)What is Jell-O made from?
- Dead animal skin and bones. They are boiled and the proteins rise up into a
thick gel. The gel is skimmed off and dried to make the gelatin.
3)Why does Jell-O wiggle?
-It is a liquid suspended in a solid matrix (colloidal suspension). Has liquid
like flow but is held firm by protein matrix
4)Why does my hand burn if I hold pineapple too long??
-The protease will actually break down some of the proteins in your hand
5)Why don’t canned pineapple affect the Jell-O?
-Protease is deactivated at high temperatures, but not at low temperatures
Comments
The students especially seemed to enjoy this activity. Suggestion: bring extra Jell-O and/or fruit that they can eat after the experiments are down. Also, leave all questions and observations until after the DNA experiment question/answer period.
B) Liver and Onions: DNA Extraction from Animal and Plant Tissues
This experiment seeks to show the students that DNA is a natural polymer that we can extract from either plant of animal tissues. Since the experiment is somewhat complex, we found that the best way to perform the experiment is divide the class into several small groups, each with their own experimental setups. Have one person who has performed the experiment previously or practiced it lead the entire group step by step through the process, stopping after each step to wait until each group is finished. So they can see that extraction can be done from a variety of tissue, it is best to give each group a different kind of sample if possible. In the same PowerPoint presentation as the Jell-O slides, there are a few slides with diagrams of DNA and a brief description of what DNA is.
Materials needed: raw beef liver, onion, banana (or similar fruit such as kiwi), distilled
water, sodium chloride (common table salt will work), sodium
bicarbonate (household baking soda will work), liquid detergent
(such as Ivory or Dove), 3 M sodium acetate solution, ethanol, scale,
blender, 50mL graduated cylinder, ice-water bath, cheesecloth,
(2) 100mL beakers, (1) 125mL Erlenmeyer flask, glass stirring rod,
test tube to hold at least 15mL, pipet, goggles, gloves
Procedure:
1)Chill 25mL of ethanol in an ice water bath
2)Prepare a carbonate buffer solution:0.75g of NaCl, 2.5g of Sodium Bicarb., 1mL of detergent, and 60mL of distilled water. Combine all ingredients and chill in an ice water bath
3)Prepare 25mL of a 3 M sodium acetate solution
**Note: It desirable to perform steps 1-3 ahead of time
4)Place 5cm3 of the material being studied (liver, onion, or fruit) in a blender with approximately 30mL of distilled water. Pulse the blender on puree for 20-30 seconds (45 seconds for fruits or vegetables) until the mixture looks like a thick milkshake
5)Transfer the mixture into the 125mL Erlenmeyer flask along with 30mL of the chilled buffer solution. Mix with the stirring rod for approximately 2 minutes.
**Note: From this point on, stirring and pouring should be done carefully since
DNAmolecules are fragile and will easily break.
6)Place a single piece of cheesecloth over the top of one of the 100mL beakers. Slowly pour the mixture in the flask into the beaker to remove any large materials.
7)Place a double-layered piece of cheesecloth over the other 100mL beaker. Pour the filtrate in the other beaker over the cheesecloth. This will remove any remaining undesirable dense particles.
**Note: If readily available, a centrifuge could be used in place of cheesecloth.
8)Transfer 5mL of the final filtrate into the test. Add 10 drops of the sodium acetate solution. Gently stir with a clean glass rod.
9)Slowly pour 6-10mL of the ice-cold ethanol down the side of the test tube.
10)Carefully watch as the DNA should appear as a separate layer between the ethanol and filtrate
11)If the DNA has not been fragmented, try to spool the DNA polymer fibers around the end of a glass pipet.
Comments
- Animal tissue will give a better yield than the fruits or vegetables. Plant tissue cell walls are more rigid and are more difficult to break down.
-The students seemed to enjoy this experiment a great deal. Further discussion can be addressed at the pleasure of the instructor.