Question

ADP is adenosine diphosphate. How many high-energy linkages (or bonds) does ADP contain? How do you know?

A. 1    

B. 2     

C. 3     

D. 4

Answer 1

ATP has one 'high-energy' bond.

Explanation:

Adenosine triphosphate (ATP) consists of the nucleobase adenine, the monosaccharide ribose and three phosphate groups.

Adenosine diphosphate (ADP) consists of the nucleobase adenine, the monosaccharide ribose and two phosphate groups.

The bond between two phosphate groups is a phosphoanhydride bond. This bond is less stable and is considered a high-energy bond. Adenosine diphosphate (ADP) can provide more energy than AMP.

ADP (Adenosine Diphosphate) contains high energy bonds located between each phosphate group. It has the same structure as ATP, with one less phosphate group. The same reasons that ATP bonds are high energy apply to ADP's bonds.

There are three reasons these bonds are high energy:

1. The electrostatic repulsion of the positively charged phosphates and negatively charged oxygen stabilizes the products (AMP + P_i) of breaking these bonds.
2. The stabilization of products by ionization and resonance. As the bonds are broken there is an increased stability due to the resonance of that product's structure.
3. The entropy increases. There is a greater stability in the products because there exists a greater entropy; i.e. more randomness. 1 mole of reactants has a higher energy than 2 moles of products. Disorder is favored over order according to the 2^nd law of thermodynamics.

In ATP there are three phosphate groups with two high-energy bonds. The bond with the outermost phosphate group has the most potential energy and is prone to hydrolysis. ATP is therefore a very good provider of energy for cellular processes. Same three reasons for high energy bonds in ATP.