Daily Newsletter February 14, 2012
Administrative Note: CPR Calibrations
Make sure you start your calibrations today. Do not wait until the last day to do all of calibrations and reviews. Give yourself time to do them. Pace yourself by doing one task each day until the close of the assignment. I have given you til Sunday to finish this task.
Daily Topic: Adenosine Triphosphate
You have most likely heard ATP referred to as the "energy currency" of the cell. In fact, your textbook uses this analogy: "Just as it is more effective, efficient, and convenient for you to trade money for a lunch than to trade your actual labor, it is useful for cells to have a single currency for transferring energy between different reactions and cell processes." This is a lovely fiction that does not serve molecular biologists. It is a convenient expression, but it conveys a very serious misconception.
Basically put, nucleotide triphosphates have their foundation in the nucleotide structure, with the addition of extra phosphate groups. Adenosine Triphosphate is the most prevalent nucleotide triphosphate. The picture below show the general structure of ATP.
You have three phosphate groups, each with a negative charge, covalently bonded to each other. The phosphate groups naturally want to repel each other, but they are held together by one of the strongest bond types. What does this mean? Molecular tension! But it must be noted that ATP is stable. It does not spontaneously loose phosphates (if it did, you would also release heat). It takes enzymatic action to remove the phosphate. When a phosphate is removed from ATP, it is generally attached to another molecular structure (enzymes, sugars, etc...). The exception to this will be in building nucleic acids.
So what is the misconception with "energy currency"? A better question will be to ask, what is energy to a cell? Cells use reducing potential for energy; electrons harvested from reduced compounds provide reducing potential. This is needed in order to make many biochemicals including ATP. What then is ATP?
The concept of ATP as an "energy currency" comes from ATP turning on enzymes or assisting an enzyme during a "power step" in a metabolic pathway. But ATP does not add energy; it just rearranges charge distribution around a molecule (electrochemistry). Remember, the phosphate group is negatively charged (-2).
As we will see in upcoming weeks, this change of shape is critical to enzyme function. You have already encountered this once before, with the Sodium/Potassium ATPase.
Daily Challenge: Function of ATP
Today, I want you to discuss the function of ATP. Do not describe it as an energy currency, instead describe how the addition of phosphates cause a change in the electrochemistry of a protein, and how that affects the conformation of the protein. Use Myosin in muscle cells as your example. We have not covered Myosin, but it is a very easy model for how ATP acts.
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