Question

Show that the hydrolysis of ATP to AMP and \(2 P_{i}\) releases the same amount of energy by either of the two following pathways. Pathway 1 \\[ \begin{array}{l} \mathrm{ATP}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{ADP}+\mathrm{P}_{\mathrm{i}} \\ \mathrm{ADP}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{AMP}+\mathrm{P}_{\mathrm{i}} \end{array} \\] Pathway 2 \\[ \begin{array}{c} \mathrm{ATP}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{AMP}+\mathrm{PP}_{\mathrm{i}}(\text { Pyrophosphate }) \\ \mathrm{PP}_{\mathrm{i}}+\mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{P}_{\mathrm{i}} \end{array} \\]

Short answer

Both pathways yield the reaction: ATP + 2H₂O → AMP + 2Pᵢ, releasing the same amount of energy.

Step-by-step solution

Write the reactions of Pathway 1

Pathway 1 involves two reactions: 1. ATP + H₂O → ADP + Pᵢ2. ADP + H₂O → AMP + PᵢCombine these reactions to get the overall reaction for Pathway 1.

Combine reactions of Pathway 1

Adding the two reactions from Pathway 1, we get: ATP + H₂O + ADP + H₂O → ADP + Pᵢ + AMP + PᵢBy canceling ADP on both sides, the overall reaction is: ATP + 2H₂O → AMP + 2Pᵢ

Write the reactions of Pathway 2

Pathway 2 involves two reactions: 1. ATP + H₂O → AMP + PPᵢ (pyrophosphate)2. PPᵢ + H₂O → 2PᵢCombine these reactions to get the overall reaction for Pathway 2.

Combine reactions of Pathway 2

Adding the two reactions from Pathway 2, we get: ATP + H₂O + PPᵢ + H₂O → AMP + PPᵢ + 2PᵢBy canceling PPᵢ on both sides, the overall reaction is: ATP + 2H₂O → AMP + 2Pᵢ

Compare the overall reactions

For Pathway 1, the overall reaction is: ATP + 2H₂O → AMP + 2PᵢFor Pathway 2, the overall reaction is: ATP + 2H₂O → AMP + 2PᵢSince both pathways yield the same overall reaction, the energy released is the same for either pathway.

Key concepts

ATP hydrolysis

ATP hydrolysis is a critical process in cells, involving the breakdown of adenosine triphosphate (ATP) through the addition of water. This reaction liberates energy that cells use to perform various functions. The equation for ATP hydrolysis is: ATP + H₂O → ADP + Pᵢ. ATP contains high-energy phosphate bonds. Breaking these bonds releases significant energy used to power cellular processes, such as muscle contractions and active transport.

ATP hydrolysis results in the production of adenosine diphosphate (ADP) and inorganic phosphate (Pᵢ).
It serves as a primary energy currency in biological systems.
It is essential for maintaining cellular energy balance.

. Understanding ATP hydrolysis helps explain how cells obtain and utilize energy from ATP molecules.

ADP

ADP, short for adenosine diphosphate, is a product of ATP hydrolysis. When ATP loses one phosphate group, it becomes ADP.
This reaction releases energy used for various cellular activities. ADP can be further hydrolyzed to AMP (adenosine monophosphate).

ADP is an intermediate energy molecule in the cell.
It can be regenerated back to ATP through phosphorylation.
It is essential for cellular respiration and photosynthesis processes.

. The interconversion between ATP and ADP forms a cycle critical to energy management in cells.

AMP

AMP, or adenosine monophosphate, is another form of adenosine phosphate. It results from the hydrolysis of ADP and ATP.
The transition from ATP to AMP involves losing two phosphate groups, reflecting significant energy release.

AMP can act as a signaling molecule in cells.
It is part of the AMP-activated protein kinase (AMPK) pathway, regulating energy homeostasis.
AMP is less energy-dense compared to ATP and ADP.

. AMP formation deepens our understanding of cellular energy distribution and use.

Pyrophosphate

Pyrophosphate (PPᵢ) is a byproduct of certain biochemical reactions, including ATP hydrolysis.
It consists of two phosphate ions linked together. During ATP hydrolysis, pyrophosphate is hydrolyzed to release more inorganic phosphate.

PPᵢ hydrolysis releases additional energy.
It plays a role in nucleotide synthesis and breaking down macromolecules.
Pyrophosphate is essential for controlling cellular energy states.
By hydrolyzing into two inorganic phosphates (2Pᵢ), pyrophosphate contributes to energy efficiency and regulation in cells.

Energy release

Energy release is a cornerstone concept in biochemistry. It explains how cells harness energy from molecules like ATP.
During ATP hydrolysis, chemical energy stored in high-energy phosphate bonds is released as ATP converts to ADP or AMP and inorganic phosphate.
The released energy powers various cellular functions.

This energy is crucial for muscle contraction, nerve impulse transmission, and biosynthesis.
It ensures that cells perform their functions efficiently.
Energy release from ATP hydrolysis is fundamental for life as it drives essential metabolic processes.
The understanding of energy release mechanisms helps grasp how living organisms sustain themselves and respond to energy demands.