Use these links to navigate to selected parts of this section of the Introductory Biochemistry module.
In non-living systems, endergonic reactions can be powered by the input of energy in a number of forms including heat and pressure.
This would be inappropriate in living cells as they are labile.
To overcome this problem, biological systems often link endergonic reactions to exergonic reactions.
In all living cells the compound used to exchange (or supply) energy for endergonic processes is adenosine triphosphate (ATP).
The anhydride bonds joining the phosphate linkages liberate large amounts of energy when hydrolysed.
ATP is hydrolysed by one of two different possible reactions. Both have the same energy yield.
ATP is hydrolysed by the removal of either the terminal phosphate in the structure above.
This reaction is :
Note: ADP = adenosine diphosphate (adenosine with 2 phosphates still attached) and Pi is an inorganic phosphate molecule.
The alternative is the removal of the TWO terminal phosphates.
This reaction is :
Note: AMP = adenosine monophosphate (adenosine with 1 phosphate still attached) and PPi is an inorganic phosphate dimer (2 phosphates joined together).
There are universal metabolic processes used by all cells to maintain adequate supplies of ATP.
The sum of the chemical reactions occurring within the body which is referred to as "metabolism" has as one of its roles the production of sufficient ATP to meet the body's needs at any time.
Muscle has an especially efficient means of ATP synthesis and utilisation.
Skeletal muscle converts chemical energy to mechanical energy with high efficiency (only 30 - 50% waste).
Muscle contraction is powered by ATP hydrolysis. ATP is available in only limited amounts.
What stops ATP levels from falling dramatically during contraction?
Muscle has a backup system (like a battery) for regenerating ATP from a compound called creatine phosphate during exercise.
During rest, normal cell metabolism synthesises ATP (from fuels like glucose) and this ATP is used to re-synthesise a reserve of creatine phosphate ready for the next burst of exercise.
This completes the section on energy currency molecules.