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McREL Standards Activity

Pineapple JELL-O?

Purpose:As a result of this activity, students will understand the importance of protein structure in determining protein function.
Related Standard & Benchmarks:
 Standard 5.Understands the structure and function of cells and organisms
   Level IV [Grade 9-12]
   Benchmark 7. Knows the structures of proteins (e.g., long, usually folded chain molecules made of specific sequences of amino acids coded by DNA) and the role of proteins in cell function
 Standard 5.Understands the structure and function of cells and organisms
   Level IV [Grade 9-12]
   Benchmark 2. Understands the chemical reactions involved in cell functions (e.g., food molecules taken into cells are broken down to provide the chemical constituents needed to synthesize other molecules; enzymes facilitate the breakdown and synthesis of molecules)
 Standard 12.Understands the nature of scientific inquiry
   Level III [Grade 6-8]
   Benchmark 3. Designs and conducts a scientific investigation (e.g., formulates hypotheses, designs and executes investigations, interprets data, synthesizes evidence into explanations)
 Standard 11.Understands the nature of scientific knowledge
   Level III [Grade 6-8]
   Benchmark 1. Understands the nature of scientific explanations (e.g., use of logically consistent arguments; emphasis on evidence; use of scientific principles, models, and theories; acceptance or displacement of explanations based on new scientific evidence)
Student Product:Lab report
Material & Resources:
Fresh, ripe pineapple, cut into small chunks
Canned pineapple (drained)
JELL-O or other gelatin product
Tap water
Large bowl
Measuring cup
Hot plate or other warming device
Ladle or other means to stir and dispense hot JELL-O
Clear glasses, beakers, or similar heat-resistant containers (two per group)
Wax pencils or other non-permanent labelling device
Stirring tools (stir rods, spoons, forks, etc.)
Pot holders/oven mitts
Teacher's Note:This activity is designed to follow introductory lectures on proteins (e.g., their structure and function) and enzymes (as a specific type of protein).  This activity assumes that students understand that canning involves very high heat and pressure.
A good recipe will caution not to add fresh or frozen pineapple, kiwi, papaya, or guava to JELL-O recipes.  This is because such tropical fruits contain a proteolytic ("protein lysing") enzyme called bromelain.  Bromelain digests the bonds between amino acids in the protein gelatin (which makes up JELL-O).  The bonds are what hold gelatin together, so when they break the gelatin falls apart.  In this experiment, students will observe this effect when using fresh pineapple, and the absence of this effect with canned pineapple.  They should use their knowledge of proteins to deduce the reason for the observed difference between the effects of the two treatments on the JELL-O.

Teacher:  When students are ready, prepare JELL-O according to package directions.  If necessary, use a hot plate (stirring frequently) to keep it warm until all students are finished.

Students can work individually or in pairs.  Students should label one container as fresh pineapple and the second as canned pineapple (labels should also include their name).  Students should carefully fill each container about half or two-thirds full with hot JELL-O.  When the JELL-O is near room temperature, students should stir in a moderate portion of the appropriate type of pineapple and carefully transfer the labelled containers to a refrigerator.

The JELL-O should be chilled for several hours, so students will observe it the next day.  If done properly, the JELL-O containing canned pineapple should appear normal, but the JELL-O containing fresh pineapple should not have set properly.

Students should write a simple lab report that includes an introduction explaining background information and the purpose of the experiment, a brief description of the methods and the results (including diagrams as appropriate), and a basic discussion in which they interpret their results and synthesize the evidence into explanations (conclusions).  In their discussions, students should show an understanding of the relation of structure to function in proteins; they should deduce that the reason the canned pineapple did not break down the gelatin bonds is because the canning process (extreme heat or boiling) broke down the bromelain enzyme, rendering it inactive.  Its structure changed and, as a result, so did its function.