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__**Cellular Energy – ATP**__ (Copy the numbered items below and fill in the blanks as you the read the following.)

ATP is the energy currency of the cell. The activities of all living things require energy. Swimming, lying, growing, reproducing, and even the flashing of a firefly use energy. Energy for cells is stored in the chemical bonds of organic molecules. The lipids, proteins, and carbohydrates in foods are the fuels that power organisms. ATP can be made from each of these three organic molecules. Since carbohydrates are the primary energy source for most cells, how ATP is made from the simple sugar glucose will be used as an example.

When glucose enters a cell, it brings with it a large supply of energy stored in its chemical bonds. In order to transfer this energy from glucose to where it is required, the cell uses a carrier molecule called ATP (adenosine triphosphate). To understand the function of ATP, it may help if you compare energy with money and a cell with a vending machine.

Suppose you try to buy something from a vending machine, but all you have is a $20 bill. Most vending machines only accept dollar bills. So change is needed before the vending machine can be operated. A similar situation exists in the cells. Sugar molecules are like $20 bills, too large for the cell to use. ATP is like the change needed to use the vending machine. The energy in ATP is is the only kind used by all cellular activities.

The structure of ATP allows it to take energy from food and then release it where it is needed. ATP is composed of the nucleotide adenosine with three phosphate groups attached to it. This is why it is called adenosine triphosphate. To release energy, the last phosphate group breaks off the ATP forming ADP, (adenosine diphosphate), a molecule with only two phosphate groups. In this way, ATP is used as a carrier molecule. Energy from food is used to attach the last phosphate group to ATP. Then the ATP molecule carries this energy to where it is required in the cell. Then the energy is used by removing the last phosphate group.

Photosynthesis is the process by which plants use the energy in light to make glucose. To store energy, as plants do during photosynthesis, ADP and a phosphate group are joined using the energy from light. The ATP made this way is then used to join carbon dioxide and water, making glucose and releasing oxygen. The food chains of almost all living things, starts with the glucose molecules made by the process of photosynthesis. Thus, ATP is required for putting energy into food as well as getting energy out of food.

ATP is the energy carrying molecule used by virtually all cells to carry out all cellular activities. It carries the energy stored in organic molecules to where these activities occur in the cell. Thinking of ATP as a rechargeable battery may help the understanding of this process. The battery releases its energy to run a radio or flashlight. Now “dead”, the battery can be recharged by adding energy from household electricity. Similarly, when ATP is converted to ADP and the phosphate group, energy is released to run the cells activities. The energy needed to recharge ATP is provided from the breakdown of food molecules like glucose. The energy in food is used to connect a phosphate group on to ADP to make it ATP again through a process called cellular respiration. Thus, ATP is the “currency” on which all cells operate.

__Reading Guide__ – Copy each item and fill in the blanks. 1. ............. is the energy currency of the cell. 2. ATP can be made from the energy in ............., lipids, and proteins. 3. Glucose has a large supply of ............. in its chemical bonds. 4. ............. carries the energy from glucose to where it is needed in the cell. 5. The energy in ATP is the only kind used by all ............. . 6. ATP is composed of the nucleotide adenosine and ............. attached phosphate groups. 7. ATP provides ............. when its last phosphate group is removed. 8. ATP gets ........... from food, carries ........... to where it is needed, and releases ........... by losing a phosphate group. 9. ............... first produces ATP which is then used to join CO2 to H2O, making glucose and releasing O2. 10. ATP is used to put energy .......... food as well as getting energy ........ of food. 11. The ............. of all living things are carried out only by the energy in ATP. 12. When ATP is changed to ADP energy is ............. for use. 13. The energy in .............is used to turn ADP back into ATP. 14. ............. is the process used to make ATP from ADP using the energy in food. 15. ATP's job is to hold and ............... small bits of energy to places in the cell were it is needed to power reactions.