Question

Would you expect the reaction ATP \(\rightarrow\) ADP \(+\) \(P_{i}\) to be accompanied by a decrease or increase in entropy? Why?

Short answer

The reaction ATP to ADP and P_{i} is accompanied by an increase in entropy because it increases the number of particles in the system.

Step-by-step solution

- Understand the Reaction

The given reaction is the conversion of ATP (adenosine triphosphate) to ADP (adenosine diphosphate) and an inorganic phosphate (P_{i}). In this process, one molecule of ATP is broken into two products: ADP and P_{i}.

- Define Entropy

Entropy is a measure of disorder or randomness in a system. A higher number of particles usually results in higher entropy because there are more ways to arrange the particles and more possibilities for disorder.

- Apply Entropy Concept to the Reaction

In the ATP to ADP reaction, the single molecule of ATP is split into two separate molecules (ADP and P_{i}). This increases the number of particles in the system from one to two, which generally increases disorder.

- Conclusion

Since the reaction increases the number of particles, it is accompanied by an increase in entropy. There are more possible ways to arrange two particles (ADP and P_{i}) compared to one (ATP).

Key concepts

Entropy in Biochemical Reactions

Entropy is a term that describes the level of disorder or randomness in a system. In biochemical reactions, this concept is very important because it helps us understand how reactions progress and why they occur. To put it simply, reactions tend to favor states where the entropy is higher. This means that if a reaction leads to an increase in the number of molecules, it's usually associated with an increase in entropy. For example, in the reaction ATP → ADP + P_i, one single ATP molecule breaks down into two products. This increases the total number of molecules in the system from one to two. Since there are now more individual molecules, there's a greater level of disorder or randomness. Thus, this reaction results in an increase in entropy.

ATP Hydrolysis

ATP hydrolysis is the process by which a water molecule breaks down ATP (adenosine triphosphate) into ADP (adenosine diphosphate) and an inorganic phosphate (P_i). This reaction is crucial because it releases energy that cells use to perform various activities like muscle contraction, protein synthesis, and cell division. ATP is considered as the energy currency of the cell because it stores energy in its high-energy phosphate bonds. When ATP is broken down to ADP and P_i, the energy stored in these bonds is released.
ATP hydrolysis is an exergonic reaction, meaning it releases energy by creating products that are more stable (ADP and P_i) than the reactant (ATP). This release of energy is very important for cellular functions and processes. All living organisms rely on this mechanism to fuel their activities.

Thermodynamics in Biochemistry

Thermodynamics is the study of energy transformations. In biochemistry, it helps to understand how and why biochemical reactions take place. One of the core concepts in thermodynamics is the Gibbs Free Energy (ΔG), which combines entropy (ΔS) and enthalpy (ΔH) into one formula: \[ ΔG = ΔH - T ΔS \]> Here, T is temperature.
For a reaction to be spontaneous (able to occur without external input), ΔG needs to be negative. When ATP is converted to ADP and P_i, the reaction is spontaneous because it releases energy (negative ΔG). The breakdown increases entropy (ΔS > 0), and usually, the enthalpy (ΔH) is negative due to breaking high-energy bonds.
Thus, the study of thermodynamics helps us understand why ATP hydrolysis is favored in biological systems. It tells us that not only is energy released, making the reaction favorable, but that entropy increases, which adds to the driving force of the reaction.