Adenosine Triphosphate (ATP) (DP IB Biology)
Revision Note
Adenosine Triphosphate (ATP)
Living organisms require energy to perform and maintain life processes such as movement, nutrition and excretion
This energy is released by the process of cell respiration
Energy released during the reactions of respiration is transferred to the molecule adenosine triphosphate (ATP)
The energy is transferred in a series of small steps
Heat is lost at each step, which is used to regulate body temperature in endotherms
ATP is a small and soluble molecule that provides a short-term store of chemical energy that cells can use to do work
Its solubility and size enables it to move easily in cells and living organisms by facilitated diffusion
It is vital in linking energy requiring and energy yielding reactions
ATP is described as a universal energy currency
Universal: It is used in all organisms
Currency: Like money, it can be used for different purposes (reactions) and is reused countless times
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
Structure of ATP
ATP is a phosphorylated nucleotide
It is made up of:
Ribose sugar
Adenine base
Three phosphate groups
ATP diagram
Structure of ATP contains ribose sugar, an adenine base and three phosphate groups
Features of ATP Table
Feature | Benefit |
|---|---|
Releases a small but sufficient quantity of energy | This is enough energy to drive important metabolic reactions while keeping energy wastage low |
Exists as a stable molecule | It doesn't break down unless a catalyst (ATPase) is present so energy won't be wasted |
Can be recycled | The breakdown of ATP is a reversible reaction, ATP can be reformed from ADP and Pi. This means the same molecule can be reused elsewhere in the cell for different reactions |
Hydrolysis is quick and easy | Allows cells to respond to a sudden increase in energy demand |
Soluble and moves easily within cells | Can transport energy to different areas of the cell |
Forms phosphorylated intermediates | This can make metabolites more reactive and lower the activation energy required for a reaction |
Examiner Tips and Tricks
Be careful not to use the terms energy and ATP interchangeably. Energy is the capacity or power to do work while ATP is a molecule which carries energy to places in the cell that need it in order to do work.
Life Processes Reliant On ATP
Some of the life processes that are reliant on ATP as a source of energy include:
In anabolic reactions to synthesise larger molecules (macromolecules) from smaller ones
To move molecules across the cell membrane against their concentration gradient during active transport
Enabling movement of the entire cell
The move cell components, such as chromosomes, within the cell
ATP is readily converted to adenosine diphosphate (ADP) and a phosphate ion (Pi), during which energy is released
Since ATP is a very reactive molecule, it is not stored in living organisms
Molecules such as glucose and fatty acids are used as short-term stores of energy, while glycogen, starch and triglycerides act as long-term storage molecules of energy
Interconversions Between ATP & ADP
ATP is a very reactive molecule and is readily converted to ADP and phosphate when releasing its energy
ADP and phosphate can then be re-converted to ATP during respiration
Organisms require a constant supply of ATP because much of the energy is lost to the surroundings as heat
ATP Cycle Diagram
The constant cycling of ATP and ADP + Pi within a cell
Hydrolysis of ATP
When ATP is hydrolysed (broken down), ADP and phosphate are produced
As ADP forms, free energy is released that can be used for processes within a cell e.g. DNA synthesis
Removal of one phosphate group from ATP releases approximately 30.5 kJ mol -1 of energy, forming ADP
Removal of a second phosphate group from ADP also releases approximately 30.5 kJ mol-1 of energy, forming AMP
Removal of the third and final phosphate group from AMP releases 14.2 kJ mol-1 of energy, forming adenosine
Hydrolysis of ATP Diagram
The hydrolysis of ATP
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
This is an energy-requiring reaction
Water is released as a waste product (therefore ATP synthesis is a condensation reaction)
Synthesis of ATP Diagram
Energy-requiring synthesis of ATP from ADP and Phosphate
Examiner Tips and Tricks
Note that you are not required to know the exact quantity of energy in kilojoules that are involved with the interconversions between ATP and ADP, but you should appreciate that it is sufficient for performing tasks within the cell.
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