J. A. BASSHAM AND M. CALVIN 



is obtained without consuming ATP, then the total requirement 

 is 2 TPNH and 2 ATP molecules, or 124 kcal.) Since the 

 energy required for the reaction 



CO2 + H2O > (C6Hi206)v. + O2 



is about +116 kcal., about 19 kcal. apparently have to be 

 expended to make the cycle operate at a high rate. The 135 



SUCROSE 



I 

 I 



* 

 HEXOSE PHOSPHATES,*^ 



I 

 I 



TRIOSE PHOSPHATES 



PENTOSE CYCLE 



PHOSPHOGLUCONIC 

 ACID'-. 



..-:»SEDOHEPTULOSE PHOSPHATES 



2 [H] <- 

 ATP 



PHOTOSYNTHETIC 

 CARBON CYCLE 



■2[H] 

 ATP 



PENTOSE PHOSPHATES* 



-ATP 



RiSULOSE DIPHOSPHATE 

 CO2 



ATP<- 



PEPA 



PYRUVIC ACID 



I 

 I 



/'x THIOCTIC ACID 



/ \^REQUIRED 



ACONITIC ACID 



ISOCITRIC ACID 



2M 



CO, 



it 



2iH] 



ACETYL 

 CoA 



CITRIC ACID 



A 

 I 



/ 



FAT 



OXALOACETIC 

 ACID 



OXALOSUCCINIC ACID 

 \ 

 \ 



\ *C02 



I 



KREBS CYCLE KETOGLUTARIC ACID 



SUCCINIC ACID 



MALIC ACID 



^ ^2 Hi 



fumaric acid 



Fig. 2. The relation of carbon paths in photosynthesis and respiration. 



kcal. (or 124 kcal.) requirement, on the other hand, represents 

 the absolute minimum of energy, which must be obtained from 

 light, exclusive of any losses in the photochemical and other 



42 



