• Energy released during the reactions of respiration is transferred to the molecule?adenosine triphosphate?(ATP)
• ATP is a small and soluble molecule that provides a?short-term store?of chemical energy that cells can use to do work
• 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

   

Hydrolysis of ATP

• Hydrolysis of ATP?to?adenosine diphosphate (ADP)?and an?inorganic phosphate?group (Pi) is?catalysed by the enzyme ATP hydrolase?sometimes called 'ATPase'
• The hydrolysis of ATP can be?coupled to energy-requiring reactions?within cells such as:
  • The active transport of ions up a concentration gradient
  • Enzyme controlled reactions that require energy
  • Muscle contraction and muscle fibre movement

   

• As ADP forms?free energy?is released that can be used for processes within a cell eg. DNA synthesis
  • Removal of one phosphate group from ATP releases 30.8 kJ mol?-1?of energy, forming ADP
  • Removal of a second phosphate group from ADP also releases 30.8 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

   

• The inorganic phosphate released during the hydrolysis of ATP can be used to?phosphorylate other compounds, often making them?more reactive

Features of ATP Table

• 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 by the enzyme?ATP synthase
  • This is an?energy-requiring reaction
  • Water is released?as a waste product (therefore ATP synthesis is a?condensation reaction)

   

Types of ATP synthesis

• ATP is made during the reactions of respiration and photosynthesis
  • All of an animal's ATP comes from respiration

   

• ATP can be made in two different ways:
  • Substrate-linked phosphorylation (occurs in the glycolysis stage of respiration)
  • Chemiosmosis (occurs in the electron transport chain stage of respiration)

轉載自savemyexams