ATP cycle

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Bio-inorganic chemistry

• ATP CYCLE

M.Prasad Naidu MSc Medical Biochemistry, Ph.D.Rese
arch Scholar
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High energy compounds

• The term high-E compounds or energy rich
  compounds is usually applied to substances which
  possess sufficient free E to liberate at least 7
  Cal/mol at pH 7.0
• The compounds which liberate less than 7.0
  Cal/mol are referred to as low-E compounds.
• Most of the high E compounds contain PO43-
  (exception acetyl CoA) hence they are called high
  E phosphate compounds.

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High E compounds
Compounds ?G0 (Cal/mol)
Phosphoenol pyruvate -14.8
Carbamoyl phosphate -12.3
Cyclic AMP -12.0
1,3bisphosphoglycerate -11.8
phosphocreatine -10.3
Acetyl phosphate -10.3
SAM -10.0
Pyrophosphate -8.0
Acetyl CoA -7.7
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Low E Phosphates
ADP?AMPPi -6.6
Glucose-1-phosphate -5.0
Fructose-6-Phosphate -3.8
Glucose-6-phosphate -3.3
Glycerol-3-phosphate -2.2

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Classification of High E compounds

• 1. Pyrophosphates e.g. ATP
• 2. Acyl phosphates e.g. 1,3-bisphosphogly
• 3. Enol phosphates e.g. PEP
• 4. Thioesters e.g. acetyl CoA
• 5. Phosphagenes e.g. phosphocreatine

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ATP CYCLE

• The living objects require a continuous supply of
  FE mainly for
• 1. to synthesize macromolecules from simpler
  smaller precursors
• 2. to transport molecules and ions across
  membranes against gradients and
• 3. to perform mechanical work, as in the muscle
  contraction etc.,

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ATP CYCLE

• The FE in these processes is derived from the
  environment.
• The phototrophs obtain this E by trapping light E
  from the SUN.
• On the other hand, chemotrophs obtain it by the
  oxidation of food stuffs.
• This FE is partly transformed into special form
  b4 it is used for biosynthesis, tpt, motion and
  fidelity.
• This special carrier of FE is ATP.
• ATP plays a central role in the transference of
  FE from exergonic to the endergonic processes in
  the cells.

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ATP CYCLE

• ATP donates much of its chemical E to energy
  requiring processes (biosynthesis, transport) by
  undergoing a breakdown to ADP and Pi.
• ATP was discovered in extracts of skeletal
  muscles by Karl Lohmann in GE and by Cyrus Fiske
  and Y.Subbarow (US) simultaneously in 1929.
• Later it was found to be present in all types of
  cells- animal, plant and microbial.

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ATP CYCLE

• Fritz.A.Lipmann a GE born US biochemist
  postulated that ATP is the 10 and universal
  carrier of chemical E in cells.(Nobel prize)
• He also first proposed the ATP Cycle , and is
  popularly known as Father of ATP cycle.
• He introduced squiggle notation to designate E
  rich bonds of biomolecules such as ATP and ADP.

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ATP CYCLE

• ATP, ADP AMP occur not only in cell cytosol but
  also in MC and the nucleus.
• ATP serves as the principal immediate donor of FE
  in biological systems rather than as a storage
  form of E.
• In a typical cell, an ATP molecule is consumed
  with in a minute of its formation.
• The turnover of ATP is very high.
• For instance , a resting human consumes about
  40kg ATP in a day.

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ATP CYCLE

• The endergonic processess such as bio- synthesis,
  active tpt etc can occur only if ATP is
  continuously regenerated from ATP
• Phototrophs harvest the FE in light to regenerate
  ATP where as chemotrophs form ATP by the
  oxidation of food stuffs.