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A2 Unit 4: Metabolism, Microbiology and Homeostasis Name: Date: Topic 4.1 The Importance of ATP – Page 2 l. ATP Production Completed 1. Go through the PowerPoint in Class 2. Read through the notes page 2-4 and complete the questions 3. Read through the BioFactsheet on Chemiosmosis and complete the

questions

4. Have a look at some past paper questions on the wikispace.

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The addition of phosphate is known as phosphorylation. ATP acts as an energy carrier in all cells and all cells use it so it is referred to as universal. ATP can be produced within cells by two methods:

• Substrate-Level Phosphorylation

And

• Chemiosmosis (used in both oxidative and photophosphorylation)

Substrate-Level Phosphorylation (SLP) Involves the transfer of phosphate from a high-energy intermediate molecule to ADP, with the aid of an enzyme. The process of forming ATP by the physical addition of a phosphate group to ADP is known as phosphorylation. ADP + Pi ATP This takes place in the cytoplasm during the first stage of aerobic respiration known as glycolysis and also within the mitochondrion in another stage of aerobic respiration known as the Krebs cycle.

Why is the synthesis of ATP described as a phosphorylation reaction? The phosphorylation of ADP to form ATP requires 30.6 kJ mol-1 of energy. The energy to power this reaction must come from somewhere within the cell. Any chemical reaction that occurs within the cell and releases 30.6 kJ mol-1 of energy and can donate a phosphate group could be used to convert ADP and Pi into ATP. What does Pi stand for? Why do you think that the letter P is not used? Using the energy from chemical reactions to produce ATP is known as substrate level phosphorylation. i.e. using the energy from substrate molecules to power phosphorylation.

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Substrate level phosphorylation takes place during glycolysis, the first stage of respiration (in the cytoplasm) and also the Krebs cycle, which takes place in the matrix of the mitochondria.

Glycolysis Krebs Cycle Looking at ATP generation in glycolysis. Using the diagram of glycolysis to outline two reactions that must produce at least 30.6 kJ mol-1 of energy and produce ATP and are hence are examples of substrate level phosphorylation reactions.

1. 2. How many substrate level phosphorylation reactions occur per turn of the Krebs cycle?

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Chemiosmosis Look at the diagram of a hydroelectric power station.

In a hydroelectric power station there is a difference in the level of water on either side of the dam wall and this is a store of potential energy. A gate is opened in a dam wall and the water flows through, turning turbines that turn generators to create electricity. In chemiosmosis ATP is generated in a similar manner. In a cell what structure do you think could act as a dam wall? In cells the difference is not with water but is created using protons (H+), so more protons are on one side of the membrane compared to the other side. This creates a gradient (a difference) in protons on one side of the membrane compared to the other. What do you think could act as a gate in the membrane? This allows the controlled flow of protons through the membrane. Attached to this membrane protein is an enzyme ATP synthetase. As the H+ ions flow through the protein pore energy is released. This energy and the enzyme ATP synthetase are used to attach a Pi group to the molecule ADP to produce ATP.

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Chemiosmosis is used in both aerobic respiration and photosynthesis. In order to create a proton gradient the energy to drive this comes from high-energy electrons. In respiration these high-energy electrons are produced from oxidation reactions and the production of ATP in this manner is known as oxidative phosphorylation. In photosynthesis these high-energy electrons are produced by the absorption of light energy and the production of ATP in this manner is known as photophosphorylation.

Protons have to be pumped into a space for chemiosmosis. In mitochondria this space is known as the intermembrane space and is found between the inner and outer membranes.

• Label this on the diagram on the left

In chloroplasts this space is found inside the thylakoid.

• Label this on the diagram

Summary Chemiosmosis requires a phospholipid bilayer, a proton pump, a proton gradient and the enzyme ATP synthetase. Energy from high-energy electrons is used to pump protons into a space either an inter membrane of a mitochondria or a thylakoid space of a chloroplast. The proton gradient is used to rotate the enzyme ATP synthetase and power the addition of a phosphate group onto ADP.

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Revision Summary for 4.1  4.1  THE  IMPORTANCE  OF  ATP  1.  Chemical  energy  is  contained  within  food  substances.    2.  Energy  may  be  converted  from  one  form  to  another.    3.  Green  plants  are  able  to  convert  light  into  chemical  energy.  All  living  organisms  are  able  o  convert  chemical  energy  to  other  energy  forms.    4.  Candidates  should  be  able  to  label  the  general  structure  of  adenosine  triphosphate  ATP):  sugar,  nitrogenous  base  and  three  phosphate  groups  joined  together.  

 5.  Energy  is  required  to  combine  ADP  and  phosphate  to  form  ATP  and  this  is  an  endergonic  reaction.  Energy  is  needed  to  make  ATP.  This  is  an  ENDERGONIC  reaction.  ATP  Synthetase  catalyses  the  reaction.  The  reaction  requires  30kJ.mol-­‐1  6.  Energy  is  released  when  ATP  is  broken  down  to  ADP  and  phosphate  and  this  is  an  exergonic  reaction;  this  is  linked  to  energy-­‐requiring  reactions  e.g.  active  transport  muscle  contraction,  synthesis  of  organic  chemicals.  Energy  is  released  when  ATP  is  broken  down.  This  is  an  EXERGONIC  reaction.  ATPase  catalyses  the  reaction.  The  breakdown  of  ATP  occurs  when  energy  is  needed.  Eg.  Active  Transport,  Muscle  Contraction,  Synthesis  of  Organic  Molecules,  Nerve  impulses    7.  Candidates  should  appreciate  the  importance  of  ATP  as  an  energy  carrier  in  cells  and  the  reason  why  it  may  be  called  the  ‘universal  energy  currency  in  living  organisms’.  ATP  is  known  as  being  Universal  as  it  is  present  in  all  organisms.  It  is  the  common  source  of  energy.  ATP  is  advantageous  due  to  it  needing  only  1  enzyme  for  energy  to  be  released,  energy  can  be  released  in  small  amounts  when  needed,  and  can  be  used  in  many  different  reactions,  increasing  efficiency  and  control  by  the  cell.  8.  Candidates  should  be  able  to  define  the  terms  ‘proton’  and  ‘electron’.  Proton  –  Positively  charged  particle  found  in  the  nucleus  of  an  atom  Electron  -­‐  Negatively  charged  particle  that  surrounds  the  nucleus  of  an  atom.  9.  ATP  is  produced  across  the  internal  membranes  of  mitochondria  and  chloroplasts.  Oxidative  Phosphorylation  –  Occurs  in  the  membranes  of  Mitochondria  in  Respiration  Photo  Phosphorylation  –  Occurs  in  the  membranes  of  the  Thylakoids  of  Chloroplasts  in  Photosynthesis  10.  In  mitochondria  the  internal  membrane  separates  the  intermembrane  space  from  the  matrix.  In  chloroplasts  the  corresponding  membrane  separates  the  thylakoid  component  from  the  stroma.  ATP  Synthetase  is  found  on  the  inner  membrane  of  the  Mitochondria,  and  on  the  thylakoid  membrane  of  the  Chloroplast.  11.  The  synthesis  of  ATP  takes  place  by  means  of  a  flow  of  protons  across  these  membranes  down  a  concentration  gradient  through  the  enzyme  ATP  synthetase  (chemiosmosis).  High  concentration  of  Protons  in  the  intermembrane  space  (Resp)  causes  them  to  diffuse  back  down  their  concentration  gradient  to  the  matrix  of  the  Mitochondria,  via  STALKED  ATP  SYNTHETASE  PARTICLES.  This  causes  the  production  of  ATP  

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12.  To  maintain  the  concentration  of  protons  in  the  inter  membrane  space,  proton  pumps  are  needed  which  are  fuelled  by  electron  energy.  Hydrogen  atoms  are  split  into  Protons  and  Electrons.  The  Electrons  are  passed  from  one  complex  to  another  by  ELECTRON  CARRIERS.  Each  time  this  occurs,  small  amounts  of  ENERGY  are  RELEASED.  This  energy  is  used  to  fuel  PROTON  PUMPS  which  pump  protons  from  the  Hydrogen  into  the  intermembrane  space.  This  creates  an  ELECTROCHEMICAL  GRADIENT  across  the  membrane.  13.  Candidates  should  be  able  to  draw  a  diagram  to  explain  the  synthesis  of  ATP  as  described  above.