Hydrolysis & Synthesis of ATP (AQA A Level Biology): Revision Note
Exam code: 7402
Hydrolysis of ATP
Energy released during the reactions of respiration is transferred to the molecule ATP
The use of ATP as an ‘energy-currency’ is beneficial for many reasons:
The hydrolysis of ATP can be carried out quickly and easily wherever energy is required within the cell by the action of just one enzyme, ATPase
A useful (not too small, not too large) quantity of energy is released from the hydrolysis of one ATP molecule - this is beneficial as it reduces waste but also gives the cell control over what processes occur
ATP is relatively stable at cellular pH levels
Hydrolysis of ATP to adenosine diphosphate (ADP) and an inorganic phosphate group (Pi) is catalysed by the enzyme ATP hydrolase, sometimes called 'ATPase'
The hydrolysis of ATP can be coupled to energy-requiring reactions within cells such as:
the active transport of ions up a concentration gradient
enzyme-controlled reactions that require energy
muscle contraction and muscle fibre movement
As ADP forms, free energy is released that can be used for processes within a cell, e.g. DNA synthesis
The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds, often making them more reactive
Features of ATP | Benefits |
|---|---|
Released a small but sufficient amount of energy | Enough to drive important metabolic reactions, without leading to wasted energy |
A stable molecule | ATP doesn't break down unless an enzyme is present, so no energy wastage |
Can be recycled | ATP can be synthesised by the condensation of ADP and Pi |
Hydrolysis is quick and simple | Cells can respond to a sudden demand for energy |
ATP is soluble | ATP can be transported to different areas of the cell for energy release |
Examiner Tips and Tricks
Do not use "energy" and "ATP" as if they mean the same thing:
Energy is the capacity to do work and cannot be created or destroyed.
ATP is a molecule that stores and transports chemical energy within cells.
Remember that reactions that need energy should be described as "using ATP" or "requiring ATP hydrolysis" and reactions that make ATP do not "produce energy"—they transfer energy into ATP molecules.
ATP synthesis
On average, humans use more than 50 kg of ATP in a day, but only have a maximum of ~ 200g of ATP in their body at any given time
Organisms cannot build up large stores of ATP, and it rarely passes through the cell surface membrane
This means the cells must make ATP as and when they need it
ATP is formed when ADP is combined with an inorganic phosphate (Pi) group by the enzyme ATP synthase
This is an energy-requiring reaction
Water is released as a waste product, therefore, ATP synthesis is a condensation reaction
ATP is made during the reactions of respiration and photosynthesis
All of an animal's ATP comes from respiration
Types of ATP synthesis
ATP can be made in two different ways:
Substrate-linked phosphorylation (occurs in the glycolysis stage of respiration)
Chemiosmosis (occurs in the electron transport chain stage of respiration)
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