ATP and Energy Release

Learning objectives:

• Recognise the structure of ATP and ADP• Understand that ATP carries energy• Understand the role of ATP in metabolic

pathways

ATP and energy releaseAdenosine triphosphate is the universal energy carrier and is required by all cells to release energy. It is composed of an adenine molecule and three inorganic phosphate molecules.

Energy is released when the end bond attaching the end phosphate is broken by an enzyme-controlled reaction into adenosine diphosphate (ADP) and a free inorganic phosphate molecule.

Adenosine Pi Pi Pi

Adenosine triphosphate

Adenosine Pi Pi Pi

Adenosine diphosphate

Energy is required to regenerate ATP from ADP andinorganic phosphate. This takes place in an enzyme-controlled reaction called phosphorylation.

When an energy-rich substance like glucose is brokendown in a living cell, it releases energy which is used toproduce ATP. This breakdown of glucose during cellrespiration is a gradual process involving many enzymecontrolled processes and this orderly release of energy isthe ideal way for the chemical energy needed to regenerateATP to be made available.

ATP is also regenerated and used during photosynthesis.

Since ATP can rapidly revert to ADP + Pi, it is able to make

energy available for energy-requiring processes such asmuscular contraction, active transport and transmission ofnerve impulses.

Oxidation and Reduction

Oxidation is the loss of hydrogen from a molecule, releasing energy.

Oxidation occurs in many metabolic pathways, e.g. respiration.

Reduction is the addition of hydrogen with the consumption of energy.

Reduction occurs during photosynthesis.

Hydrogen removedOXIDATION

Energy released

Substrate reduced Substrate oxidised

Hydrogen addedREDUCTION

Energy consumed

OxidationIsLossReductionIsGain

• Answer question 2 from Questions on page 19 of Torrance to form part of your notes