3.1.6 ATP

• Plant and animal cells need energy for

  biological processes to occur
• Plants need energy for things like

  ● active transport — e.g. to transport solutes from their leaves● DNA replication ● cell division ● protein synthesis
• Animals need energy for things like

  ●active transport — e.g. to absorb glucose from the ileum epithelium into the bloodstream ● DNA replication ●cell division ●protein synthesis
• Respiration


  the process of plant and animal cells releasing energy from glucose
• A cell can't get its energy directly

  from glucose
• In respiration, the energy released from glucose is used to

  make ATP — adenosine triphosphate
• ATP is made from


  ●the nucleotide base adenine ●a ribose sugar ●three phosphate groups— known as a nucleotide derivative because it’s a modified form of a nucleotide

  
• Once made, ATP diffuses


  to the part of the cell that needs energy
• The energy in ATP is stored in

  high energy bonds between the phosphate groups — released via hydrolysis reactions
• nucleotide derivative

  modified form of a nucleotide
• The structures of

  
• Inorganic Phosphate


  a single phosphate

  
• When energy is needed by a cell, ATP is broken down into

  ● ADP (adenosine diphosphate) ● Pi (inorganic phosphate)— This is a hydrolysis reaction

  
• When ATP is broken down

  ● a phosphate bond is broken ● energy is released— reaction is catalysed by the enzyme ATP hydrolase

  
• ATP hydrolysis can be 'coupled' to other energy-requiring reactions in the cell


  means the energy released can be used directly to make the coupled reaction happen— rather than being lost as heat
• Phosphorylation


  when the released inorganic phosphate is added to another compound — often makes the compound more reactive
• ATP can be resynthesised in

  a condensation reaction between ADP and Pi— happens during both respiration and photosynthesis— catalysed by the enzyme ATP synthase

  
• AMP, ADP, ATP

  ● Adenosine monophosphate — has one phosphate● Adenosine diphosphate — has two phosphates● Adenosine triphosphate — has three phosphates
• In a cell there's a constant cycle between


  ● ADP and Pi ● ATP— allows energy to be stored and released as it’s needed

  
• ATP is a store of energy


  ● Energy is used to make ATP● released when ATP is hydrolysed to ADP and Pi

  
• ATP releases a small but sufficient amount of energy (75.8 kj mol-¹ from the complete hydrolysis of ATP)


  ● enough energy to drive important metabolic reactions● while keeping energy wastage low
• ATP exists as a stable molecule


  ● doesn't break down unless a catalyst (ATPase) is present— so energy won't be wasted
• ATP can be recycled


  ● the breakdown of ATP is a reversible reaction — ATP can be reformed from ADP and Pi ● means the same molecule can be used elsewhere in the cell for different reactions
• ATP hydrolysis is quick and easy


  allows cells to respond to a sudden increase in energy demand
• ATP is soluble and moves easily within cells


  can transport energy to different areas of the cell
• ATP forms phosphorylated intermediates


  ● can make metabolites more reactive● lower activation energy required for a reaction