Phosphate Esters and Anhydrides

Phosphate esters and anhydrides

Major concepts

·  Phosphoanhydrides are theromodynamically unstable and are considered “high energy compounds” because their hydrolysis is highly exothermic

·  Phosphate esters and phosphate diesters are thermodynamically unstable, but are lower energy phosphate containing molecules because their hydrolysis is less exothermic

·  ATP is an energy currency molecule because they are kinetically stable and thermodynamically unstable

·  Unfavorable reactions can be driven by being coupled to thermodynamically favorable reactions

Vocabulary

·  Phosphoanhydride

·  Phosphomonoester

·  Phosphodiester

·  High energy bond

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Students should be able to:

·  Recognize phosphate anhydrides and esters

·  Rank relative stabilities of various phosphate containing compounds

·  Predict the products of phosphate hydrolysis

·  Predict the products of phosphate transfer reactions

·  Determine if a phosphate transfer reaction is exothermic or endothermic

Daily Problems

1. Explain why this reaction is energetically far downhill by explaining the relative stability of the starting material and products.

There is more resonance stabilization in the products than in the reactants. Separated phosphates are solvated by water more readily. There is less ionic repulsion in the product.

2. Label the phosphate anhydrides, phosphate monoesters, and phosphate diesters in these molecules. Indicate all that are considered “high energy” bonds.

3. If these compounds are completely hydrolyzed, what is the product? Does it cost a high energy bond or not? If so, how many?

4. If phosphate is transferred from ATP to these molecules, we say they are “phosphorylated.” Draw the structures.

5. Keeping in mind that ADP is the side product for each of the reactions in question 3, are those reactions exothermic or endothermic? How do you know?

All of the reaction in question three are exothermic. We can see this by counting the change in high energy bonds.

1 and 2) Adenosine (no high E bonds) + ATP (2 high E bonds)→3’(or 5’) AMP (no high E bonds) + ADP (1 high E bond)

3) fructose (no high E bonds) + 2 ATP (4 high E bonds) → F-1,6-bisphosphate (no high E bonds) + 2 ADP (2 high E bonds)

6. Do these reactions cost a high energy phosphate bond, produce a high energy phosphate bond, or have no net cost/production?