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ATP

Unit 4 - Populations and the environment
2 ATP
• ATP is used as the energy source to carry out essential processes
• Energy is the ability to do work
• Organisms need energy for:
- metabolism - reactions in the body involving energy
- movement - within (circulation of blood) and of the organism (locomotion)
- active transport
- maintenance, repair and division - of cells and organelles
- production of substances - enzymes, hormones
- maintenance of body temperature - in birds and mammals, endothermic, need
energy to replace that lost as heat
• Flow of energy
1
...
Chemical energy in the form of organic molecules converted into ATP during
respiration in all cells
3
...
When they break they release energy
...


Energy released for use by cells

Hydrolysis

ATP Synthesis
• ATP -> ADP + Pi is a reversible reaction
• energy can be used to add an
inorganic phosphate to ADP to re-form ATP
• This is a condensation reaction
- water is eliminated

ATP

ADP + Pi
Condensation

Energy supplied from respiration

1

ATP
The addition of a phosphate molecule occurs in 3 ways:
1
...
Oxidative Phosphorylation - in mitochondria during electron transport chain
3
...
E
...
the formation of pyruvate at
the end of glycolysis
• In 1
...
ATP is synthesised during the transfer of electrons along a chain of electron
carrier molecules
Roles of ATP
• Not a good energy store as phosphate bonds are unstable
• Fats, carbohydrates such as glycogen are better energy stores
• ATP is the immediate energy source so cells do not store large quantities of ATP but
maintain a few seconds’ supply
• ATP is a better energy source than glucose because:
• ATP releases less energy so energy for reactions is released in smaller, more
manageable quantities
• Hydrolysis of ATP is a single reaction and can therefore be broken down to
release energy more quickly
• However, ATP cannot be stored so it has to be continuously made within mitochondria
• ATP is the source of energy for:
• metabolic processes
- E
...
polysaccharides from monosaccharides, polypeptides from amino
acids, DNA/RNA from nucleotides
• movement
- E
...
muscle contraction - ATP provides energy for filaments of muscle to
slide past one another and therefore shorten the overall length of a muscle
fibre
• active transport
- E
...
ATP provides energy to change the shape of carrier proteins
• secretion
- ATP is needed to form lysosomes
• activation of molecules
- When a phosphate molecule is transferred to another molecule, it makes it
more reactive thereby lowering the activation energy allowing enzymecatalysed reactions to occur more readily
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g

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