Energy in the Bonds of ATP Instructions Read through the background information and procedure carefully. Answer the pre-­‐lab questions, implement the procedure, and then complete the graph and analysis questions. Introduction Energy is the ability to do work. Potential energy is energy of position or stored energy and it can be converted into kinetic energy. Kinetic energy is energy of motion. Chemical bond energy, a type of potential energy, is the energy stored in the bonds of molecular substances. In cellular respiration and photosynthesis cells produce chemical bond energy. Imagine that you are standing on the second floor of a building. You have potential energy due to your position – and the taller the building, the greater the potential you would have. You can convert it to kinetic energy all at once by jumping to the floor below, or you can release it a little at a time by walking down the stairs. The problem is that the release of the chemical bond energy of carbohydrates in a cell must be done in a manner that does not destroy the cell during the process. In cells, potential energy in the chemical bonds of food is transferred to the bonds of a substance called adenosine triphosphate (ATP). Adenosine triphosphate is the most common energy-­‐storing molecule in the cell. ATP is constructed from a nucleotide called adenine and a sugar called ribose. Together, the adenine and ribose are called adenosine. It is called triphosphate because of the three phosphates – the same molecules as in phospholipids – attached to the adenine and ribose. Adenine + Ribose + 3 Phosphates = A-­‐P~P~P Two other molecules in the cell are related to ATP: ! Adenosine diphosphate (ADP) has two phosphate groups attached to it: A-­‐P~P ! Adenosine monophosphate (AMP) has a single phosphate group: A-­‐P When organisms need energy, they split the third phosphate group off from ATP to form ADP and a single phosphate. The energy from the breaking bond is used to power many cellular processes. Materials and Methods 1 Large block (A) Meter stick 3 Small blocks (P’s) Safety glasses Scissors 3 Rubber band
1. Use three rubber bands to represent the chemical bonds holding the phosphates to the adenosine molecule. The first rubber band goes around the adenosine block and one phosphate block. The second rubber band goes around the adenosine and two phosphate blocks. The third rubber band goes around the adenosine and all three phosphate blocks. 2. Cut the rubber bands in with scissors to simulate the breaking of bonds. Start with the band encircling all three phosphates. Then cut the rubber band circling two phosphates. Finish with the rubber band circling one phosphate. 3. Measure the distances the rubber bands traveled, which represents the amounts of energy in the molecule. Record the results in your data table. Pre-­‐Lab Questions 1. Which is displaying potential energy: an aluminum can sitting on a high shelf or an aluminum can falling to the ground? Which is displaying kinetic energy? Why? 2. What does ATP stand for? What is the main function in the cell? How many phosphate groups does it have? 3. What do the rubber bands in this experiment represent? Which rubber band do you expect will travel the greatest distance? Which will travel the shortest distance? Why? 4. Think of the analogy of a person jumping from a building versus a person going down the stairs. Which releases energy more quickly? What dangers does the quick release of energy bring? With that in mind, why might a cell want to break down carbohydrates into energy in steps rather than all at once? Results Molecule Rubber Band around ATP Rubber Band around ADP Rubber Band around AMP Distance Traveled (cm) Class Averages of Distance Traveled (cm) On graph paper, draw a bar graph with Energy Released (in cm) on the y-­‐axis and Molecule on the x-­‐axis. Include both your group’s data and the class averages. Analysis Questions 1. Which rubber band traveled the farthest? 2. Which rubber band had the greatest potential energy? The least? 3. Which rubber band had the greatest kinetic energy? The least? 4. Based on your results above, which bond has the greater amount of potential energy: the bond between the 1st and 2nd phosphate or the bond between the 2nd and 3rd phosphate? Which has the greater amount of kinetic energy? How do you know? 5. Based on your results, which has a greater amount of energy: ADP or ATP? How do you know? 6. Based on your results and what you know about ATP, explain in terms of potential and kinetic energy why an athlete needs to eat more than a couch potato.