• Power Points:  Cell Respiration # 1
                            Cell Respiration # 2
     Cellular Respiration, Bozeman (14:13) http://www.youtube.com/watch?v=Gh2P5CmCC0M
     Anaerobic Respiration/Fermentation, Bozeman (7:59)   http://www.youtube.com/watch?v=cDC29iBxb3w
    KEY to Cell Energy (make an ATP molecule) activity:   ATP model  Cells Energy
    ATP provides energy fpor cellular work. pages 143-144


    • Describe the structure of ATP and how it stores energy.
    • Give examples of work that cells perform.
    • Summarize the ATP cycle.


    Key Term


    It's a good thing that food doesn't fuel your cells by burning like the torched peanut described in Concept 7.2. In fact, the carbohydrates, fats, and proteins obtained from food do not drive work in your cells in any direct way. The chemical energy stored in these compounds must first be converted to energy stored in another molecule.

    How ATP Packs Energy
    As you read in Chapter 6, ATP stands for adenosine triphosphate. The "adenosine" part consists of a nitrogen-containing compound called adenine and a five-carbon sugar called ribose (Figure 7-9). The triphosphate "tail" consists of three phosphate groups. The tail is the "business" end of ATP—it is the source of energy used for most cellular work.

    Figure 7-9
    Figure 7-9
    An ATP molecule contains potential energy, much like a compressed spring. When a phosphate group is pulled away during a chemical reaction, energy is released.


    Each phosphate group is negatively charged. Because like charges repel, the crowding of negative charge in the ATP tail contributes to the potential energy stored in ATP. You can compare this to storing energy by compressing a spring. The tightly coiled spring has potential energy. When the compressed spring relaxes, its potential energy is released. The spring's kinetic energy can be used to perform work such as pushing a block attached to one end of the spring.

    The phosphate bonds are symbolized by springs in Figure 7-9. When ATP is involved in a chemical reaction that breaks one or both of these phosphate bonds, potential energy is released. In most cases of cellular work, only one phosphate group is lost from ATP. Then the tail of the molecule has only two phosphate groups left. The resulting molecule is called adenosine diphosphate, or ADP.

    ATP and Cellular Work
    During a chemical reaction that breaks one of ATP's bonds, the phosphate group is transferred from ATP to another molecule. Specific enzymes enable this transfer to occur. The molecule that accepts the phosphate undergoes a change, driving the work.

    Your cells perform three main types of work: chemical work, mechanical work, and transport work (Figure 7-10). An example of chemical work is building large molecules such as proteins. ATP provides the energy for the dehydration synthesis reaction that links amino acids together. An example of mechanical work is the contraction of a muscle. In your muscle cells, ATP transfers phosphate groups to certain proteins. These proteins change shape, starting a chain of events which cause muscle cells to contract. An example of transport work is pumping solutes such as ions across a cellular membrane. Again, the transfer of a phosphate group from ATP causes the receiving membrane protein to change shape, enabling ions to pass through.

    Figure 7-10
    Figure 7-10
    The energy in ATP drives three main types of cellular work.


    The ATP Cycle
    ATP is continuously converted to ADP as your cells do work. Fortunately, ATP is "recyclable." For example, ATP can be restored from ADP by adding a third phosphate group (Figure 7-11). Like compressing a spring, adding the phosphate group requires energy. The source of this energy is the organic molecules from food. Thus, ATP operates in a cycle within your cells. Work consumes ATP, which is then regenerated from ADP and phosphate.

    Figure 7-11
    Figure 7-11
    ATP is constantly recycled in your cells.


    The ATP cycle churns at an astonishing pace. A working muscle cell recycles all of its ATP molecules about once each minute. That's 10 million ATP molecules spent and regenerated per second! The next concept focuses on how your cells keep pace with this incredible demand for ATP.

    Concept Check 7.3
    1. In what way is ATP like a compressed spring?
    2. List three main types of cellular work.
    3. What is the source of energy for regenerating ATP from ADP?


                                                      Cell Respiration Lab  

                                      Average Number of Drops of NaOH

     Individual              Resting 5 Minutes         After 3 Minutes of Exercise

    1.    Cheyenne                                      11                                  15

    2.    Nick                                        10                                  16

    3.    Jeremy                                     9                                15    

    4.    Kelli                                         10                               15    

    5.    Lindsey                                     2                                    3

    6.    BILLY                                        20                                   4

    7.    Molly                                      14                                  13

    8.    Rich                                         11                                  10

    9.    Jamiera                                    14                                  13

    10.  D’Andre                                 11                                   10

    11. Joe                                          17                                  31

    12. John                                       15                                  21

    13. Elizabeth                                8                                      3

    14. Shannon                                10                                    9

    15. Jake                                        12                                  14

      Average:     174 / 15 = 11.6                    192  / 15 =  12.8