University:
Cambridge College
Course:
SCI 225W | Foundations in Biology
Academic year:

2023
Views:

388

Pages:

2
Author:

M Theodore

Dark reaction (Calvin-Benson cycle) The metabolic pathway for the reaction of forming glucose from CO2 is called the cycle Calvin. In adding CO2, several reaction stages occur, namely: Stage I : 6 molecules of CO2 from the air react with 6 molecules of ribulose 1.5 diphosphate, catalyzed by the enzyme ribulose diphosphate carboxylase to produce 12 molecules of 3 phosphoglycerate. Stage II: 12 3 phosphoglycerate molecules catalyzed by the enzyme phosphoglycerate kinase and glyceraldehyde phosphate dehydrogenase will form 12 glyceraldehyde 3 phosphate molecules with the help of 12 ATP and 12 NADPH. Stage III 12 glyceraldehyde 3 phosphate will be converted into 3 molecules of fructose6phosphate,the fructose 6 phosphate will be converted into glucose. The overall reaction equation is as follows: 6CO2 +18ATP + 12 NADPH + 12H+ +12H2O 18Pi+18ADP+12NADP+ Glucose + In general, the relationship between light reactions and dark reactions is that solar energy captured by photosystems I and II in the bright phase of light is converted into chemical energy NADPH and ATP.Three types of synthetic reactions that have been identified in plants are C3 , C4 and CAM. 1) C4 Cycle The C4 cycle is also called the Hatch-Slack metabolic pathway, namely the CO2 docking metabolic pathway which in its first reaction stage involves the formation of dicarboxinic acids with four carbon atoms, namely oxaloacetic, malic and aspartic acids.The C4 cycle occurs in class C plants, such as corn,grasses and desert plants. The following is the C4 cycle metabolic pathway . Information E1 = carbonic antidrase E2 = phosphoenolpyruvate carboxylase E3 = transaminases E4 = pyruvate dikinase E5 =E6 = malate dehydrogenase 2) C3 Cycle The C3 cycle occurs in legumes, wheat and rice. This cycle begins with CO2 fixation , namely combining CO2 with a carbon acceptor molecule. But in this cycle CO2 is fixed to five-carbon sugar, namely ribulose bisphosphate (RuBP) by the RuBP carboxylase enzyme (rubisco). The 6 carbon molecule formed is unstable and immediately separates into 2 phosphoglycerate (PGA) molecules. The PGA molecule is a three-carbon stable carbohydrate first formed so this method is called the C3 cycle .RuBP + CO2 rubisko 2PGA 3) CAM CAM (Crassulacean Acid Metabolism) is the mechanism that occurs least frequently among the three cycles (C3 , C4 , CAM).This cycle occurs in pineapple plants, cacti, lilies, agave, and several types of orchids.Biochemically, the CAM cycle is identical to the C4 cycle , except that there is no separation of synthesis reactions between the mesophyll and the sheath cell bundles. In fact, all reactions are separated by time, a factor that is very important for the survival of CAM plants in dry environments.

Dark Reaction (Calvin-Benson Cycle)

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