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  • Created by: Megan
  • Created on: 24-04-14 09:13


...the process that occurs in living cells which releases the stored energy in comple organic molecules and uses it to synthesise ATP

Energy (j or Kj) :- the ability to work (it cannot be created or destroyed)

What it used for?

  • Metabolism
  • For catabolic and anabolic processes
  • Active Transport
  • Exocytosis and Endocytosis
  • Movement - undulipodia/muscle contraction
  • Activation of chemicals
  • DNA replication
  • Heat - to maintain optimum temperatures for enzyme activity
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...the molecular unit of currency in all cells...

ATP is a modified nulceotide and has 2 phosphate groups added by phosphorylation. Removal of the first 2 phosphate groups releases 30.6KJ/Mol but removing the third releases only 14.2KJ/Mol


  • IT transporrts chemical energy for metabolism
  • Stores energy as chemical potential energy when it is synthesised by ATP synthase (ATPase) in a condensation reaction
  • Releases energy when hydrolysed

The energy that is released is in small amounts that are:

  • immediately usable by the cell (in amounts required by metabolic reactions) so is not wasted
  • unlikely to damage cells (through heat given off)
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There are around 60g of ATP in your body - ATP is not a long term storage molecule like carbohydrates and fats, it is an energy shuttle

ATP to ADP is a single reaction, where as the breakdown of glucose molecules is a series of complex reactions. THis also takes longer. A small amount of useful energy  is released from ATP. Glucose would produce more energy than is required.

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occurs in the cytoplasm. Glucose (6C) is converted into two molecules of Pyruvate (3C) - uses 2 ATP moleucles and makes 4 ATP molecules so the net yield is 2 ATP (substrate level phosphorylation). Two molecules of NAD are reduced

1) Phosphorylation - uses ATP to kick start the process

  • C6 of Glucose gains a phosphate group to from a hydrolysed ATP to form GLucose-6-Phosphate
  • Unstable Glucose-6-Phosphates changes into Fructose -6-Phosphate
  • Fructose 1,6 Bisphosphate (activated, phosphorylated hexose) is formed by using energy and Pi from another ATP

2) Splitting hexose 1,6 - Bisphosphate - Hexose 1,6 Bisphosphate splits into two moleucles of triose phosphate (3C)

3) Oxidation of Triose Phosphate

  • Dehydrogenase enzymes remove 2 hydrogen atoms from each triose phosphate molecule with the help of 2 NAD Molecules as Hydrogen acceptors. 2 moleucles of NADH are produced and 2 molecules of ATP are made

4) Conversion of Triose Phosphate to Pyruvae - Each triose phosphate molecule is converted, by enzyme controlled reactions, into Pyruvate (3C). 2 molecules fo ATP are produced

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Link Reaction

occurs in the matrix of the mitochondria. One molecule of Pyruvate (3C) wiil combine with Coenzyme A relaseaing one molecules of carbon dioxide to form Acetyl Coenzyme A (2C). This reduces one molecule of NAD to NADH

1) Pyruvate (3C) is decarboxylated to form acetate (2C) and the waste product C02. Pyruvated is also dehydrogenated to donate a H atom to NAD, which is reduced.

2) Acetate (2C) combines with CoA to form Acety CoA (2C). This is eeded to carry acetate in the Krebs cycle.

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Krebs Cycle

Occurs in the matrix. ATP produced by substrate level phosphorylation and NAD and FAD moleucels are reduced. Carbon dioxide is produced by decarboxylation. Oxaloacetate (4C) is regnerated. The cycle occurs twice per glucose molecule.

1) Acetate (2C) combnies with oxaloacetate (4C) to form citrate (6C). Conenzyme A goes back to the link reaction

2) Citrate (6C) is decarboxylated as cardon dioxide is removed. Citrate (6C) is also dehydrogenated as it donates a hydrogen atom to NAD which is reduced. Alpha Ketogluterate (5C) is formed.

3) Alpha Ketogluterate (5C) is decarboxlyated as carbon dioxide is produced and dehydrogentated to donate hydrogen atoms to NAD which is reduced. Succinyl CoA (4C) is formed

4) Succinyl CoA (4C) is converted to succinate (4C) and in the process donates a phosphate group to ADP to form ATP (Substrate level phosphorylation)

5) Succinate (4C) is dehydrogenated to donate a pair of hydrogen atoms to the Coenzyme FAD, this is reduced to form FADH. A new 4C compound, Malate, is formed

6) Malate (4C) is dehydrogenated to donate a hydrogen atom to NAD which is reduced. Oxaloacetate (4C) is regenerated.

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Oxidative Phosphorylation

...the formation of ATP by adding a phosphate group to ATP, in the presence of oxygen, which is the final electron acceptor.

1) Electron carriers are embedded into the inner mitochondrial membrane called the cristae, increasing the surface area for electron carriers and ATP synthase enzymes

2) NADH and FADH are oxidised. The donated hydrogen atom splits into protons and electrons

3) Electron Transport Chain:- The electrons are passed along a chain of electron carriers and then donated to molecular oxygen. The final electron acceptor. The first electron carrier to accept electrons from NADH is a protein complex, complex 1, called NADH-coenzyme Q reductase or NADH dehydrogenase

4) Chemiosmosis:- As electrons flow along the ETC, energy is released and used, by coenzymes associated with some fo the electron carriers (complexes I, II and IV) its pumps the protons across to the intermembrane space. 

5) This builds up a proton gradient which is also a pH gradient and an electrochemical gradient. Thus, potential energy builds up in the intermembrane space. The H+ ions cannot diffuse through the lipid part of the inner membrane so diffuse through ion channels - ATP synthase, into the matrix.

6) Oxidative Phosphorylation:- as protons flow through an ATP synthase enzyme, they drive the rotation of part of the enzyme and join ADP and Pi to form ATP. The electrons are passed from the last electron carrier in the chain to molecular oxygen which is the final electron acceptor

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ATP produced

32 molecules of ATP should be produced - 2 from Glycolysis, 2 from the Krebs cycle, 28 from Oxidative Phosphorylation

Why this is not always produced?

  • Protons leak across the membrane so there is less proton motive force
  • ATP is used for active transport of pyruvate from the cytoplasm into the mitochondria
  • ATP used to shuttle NaDH from cytoplasm into the mitochondria
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