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7.3 outline the discovery of ATP synthesis in the mid 20th century in terms of: the discovery of photophosphorylation in chloroplasts of plants the discovery that ATP synthesis involves an electron transfer reaction occurring across a membrane

outline the discovery of ATP synthesis in the mid 20th century in terms of:

  • the discovery of photophosphorylation in chloroplasts of plants
  • the discovery that ATP synthesis involves an electron transfer reaction occurring across a membrane
  1. In your research you may have read the terms ”cyclic” and “non-cyclic” when referring to photophosphorylation. Cyclic photophosphorylation is less than 5% of the rate of non-cyclic photophosphorylation, depends only on PS I and does not produce NADPH. The notes provided here, refer to non-cyclic photophosphorylation.
  2. Mitchell was not able to prove the proton gradient produced ATP when he proposed his hypothesis. Later experiments using change in hydrogen ion concentration (pH) and mitochondria showed that ATP was produced when the H+ crossed the membrane. Peter Mitchell was awarded the Nobel Prize in 1978 for his proposal of what by that time had become the chemiosmotic theory.
  3. The increased pH is equivalent to a reduced H+ ion concentration on the outside of the chloroplast. The H+ ions move out of the chloroplast along the concentration gradient by diffusion (from more concentrated to less concentrated). This change in pH was meant to be equivalent to the effect of the light dependent reaction on the chloroplasts.