Question

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

Short answer

The reaction \( \text{ATP} \rightarrow \text{ADP} + \text{P}_{\text{i}} \) results in an increase in entropy because it produces more molecules.

Step-by-step solution

Understand Entropy

Entropy is a measure of the disorder or randomness in a system. Higher entropy means more disorder.

Analyze the Reaction

The given reaction is \( \text{ATP} \rightarrow \text{ADP} + \text{P}_{\text{i}} \). Here, one molecule of ATP breaks down into two separate molecules: ADP and an inorganic phosphate (Pi).

Compare Number of Molecules

Initially, there is one molecule of ATP. After the reaction, there are two separate molecules (ADP and Pi). Breaking one molecule into two increases the number of particles in the system.

Determine Change in Entropy

An increase in the number of particles generally leads to increased disorder. Hence, breaking ATP into ADP and Pi results in an increase in entropy.

Key concepts

ATP hydrolysis

ATP hydrolysis is a crucial reaction in biochemistry. It involves the breakdown of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and an inorganic phosphate (Pi). This reaction releases energy, which cells use for various processes like muscle contraction and protein synthesis.
In the reaction, the chemical bonds holding the phosphate groups together in ATP are broken, releasing energy that was stored in those bonds.
Because ATP hydrolysis is exergonic, or energy-releasing, it is often coupled with endergonic (energy-consuming) reactions to help drive them forward. This coupling is central to energy transfer in biological systems.

entropy

Entropy is a measure of disorder or randomness within a system.
In general, systems tend to move toward a state of higher entropy over time.
The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time.
In the context of biochemical reactions like ATP hydrolysis, an increase in entropy usually means a larger number of molecules or a greater distribution of energy states in the system. When ATP breaks down into ADP and Pi, the number of molecules increases from one to two, leading to higher disorder and thus higher entropy.

biochemical reaction analysis

Analyzing a biochemical reaction involves looking at the reactants and products, and considering how they change during the reaction.
For ATP hydrolysis, the reactant is one molecule of ATP and the products are one molecule of ADP and one inorganic phosphate (Pi).
This transformation provides insight into how energy is released and used in biological systems. The breakdown of ATP increases the number of particles in the system, which generally leads to an increase in entropy. Additionally, understanding the energy changes involved can help explain why ATP is such an efficient energy carrier.

ADP

ADP stands for adenosine diphosphate, which is a product of ATP hydrolysis.
It consists of adenine, ribose (a sugar), and two phosphate groups.
ADP plays a pivotal role in cellular metabolism because it can be converted back into ATP through processes like cellular respiration and photosynthesis.
This recycling of ADP into ATP allows cells to maintain a constant supply of ATP, which is critical for sustaining energy-requiring activities. When ADP is phosphorylated to form ATP, energy is stored in the newly created phosphate bond.

inorganic phosphate

Inorganic phosphate (Pi) is another product of ATP hydrolysis.
It is a simple phosphate ion that can be used in various cellular processes.
Inorganic phosphate can combine with ADP to form ATP in processes like oxidative phosphorylation and substrate-level phosphorylation.
It also plays a role in signaling pathways, enzyme regulation, and cellular structure. In sum, the production and utilization of inorganic phosphate during ATP hydrolysis and synthesis are vital for cellular energy management.