Question

The substance 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) is a photosynthetic inhibitor. Choose the correct statement about DCMU based on the above information:

• A. It can not block non-cyclic photophosphorylation
• B. It will have effect on the cyclic photophosphorylation
  
• C. It inhibits electron flow from plastoquinones to cytochrome $b_{6}f$
  
• D. It inhibits photolysis of water
  

Answer 1

The correct option is C It inhibits electron flow from plastoquinones to cytochrome $b_{6}f$


In non-cyclic photophosphorylation, the high energy electron passes from plastoquinone to cytochrome $b_{6}f$. DCMU competes with the plastoquinone for the binding site of platoquinone on cytochrome $b_{6}f$ and inhibit non-cyclic photophosphorylation.

Since, plastoquinone is not a part of cyclic photophosphorylation, DCMU can not block cyclic photophosphorylation.