Chemiosmotic Hypothesis – Class 11 | Chapter – 13 | Biology Short Notes Series PDF

Chemiosmotic Hypothesis: The chemiosmotic hypothesis is a biological mechanism proposed in 1961 by a British biochemist named Peter Dennis Mitchell.

  • It is the mechanism by which ATP molecules are synthesised by the activity of ATP synthase.
  • It is a process that describes how ATP molecules or energy molecules are formed as a result of the process of photosynthesis.
  • The Nobel Prize in Chemistry was granted to the biochemist for his important contributions to the discipline of Biology, since his study gave a clearer understanding of the complete process of the Chemiosmotic hypothesis.

The Process of Chemiosmotic Hypothesis

The proton gradient that prevails across the thylakoid membrane causes ATP: Adenosine triphosphates to be generated throughout this process. Proton gradient, ATP synthase, and proton pump are three essential components for the chemiosmosis process. ATP synthase is the enzyme that is needed for the formation of ATP molecules.

F0 and F1 are the 2 subunits of the ATP synthase enzyme. The F0 subunit is implicated in proton transport across the membrane, which results in changes in F1 structure and enzyme activation. The enzyme phosphorylates ADP (adding a phosphate group) and transforms ADP to ATP. ATP synthase is primarily driven by the proton gradient that develops throughout the membrane.

Photosystems assist chlorophyll absorb light during the light response phase of photosynthesis. This causes hydrolysis, in which water molecules are torn apart, releasing electrons and protons. The liberated electrons are energised and proceed to a higher energy level, where the electron transport system gives them away.

Meanwhile, the stroma’s discharged protons begin to accumulate within the membrane. As a result, a proton gradient is created, which is a product of the electron transport chain. Photosystem I use a little amount of the resulting protons to convert NADP+ to NADPH using electrons obtained from water photolysis. The proton gradient eventually collapses, releasing energy and protons that are transported back to the stroma via ATP synthase F0. The energy released causes changes in F1 conformation, which initiates the ATP synthase, which transforms ADP to ATP.

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By Team Learning Mantras