ENERGY TRANSFERS AND BIOLOGICAL OXIDATIONS 



169 



anaerobic 



lactate 

 -■^ othanol 



CHgCOCOO' 



pyi-uvate 



ATP-e^. 



pyruvic 

 kinase / 



ADP- 



Mg 



+ + 



OPO3H- 



I 

 CH2=CC00~ 



phosphoenolpyruvate 



HOPO3- 



triosephosphate 



dehydrogenase 



aerobic 



citric acid 

 cycle 



enolase 



Mg 



+ + 



HoO 



CH2OPO3H 

 CHOH 



alanine 

 ->- acetate 



fats 



OPO3H- 



HOCH2CHCOO- 



2 - phosphoglycerate 



A 



2, 3-diphosphoglycerate 



+ 

 phosphoglyceromutase 



^ 3-phosphoglyceric ^-HOgPOCH^CHOHCQQ- 



DPN' 



COOPO3- 



DPNH 1, 3-diphospho- 

 glycerate 



kinase 

 Mg+ + 



ADP ATP 



3 - phosphoglycerate 



All except the first of these five divisions are illustrated and dis- 

 cussed in the following individual sections. 



Glycolysis. The biological reactions grouped under the heading of 

 intermediate metabolism serve to transform a variety of carbohydrates 

 into pyruvate, certain related low-molecular-weight substances, and 

 carbon dioxide. The carbohydrates concerned include those assimi- 

 lated from the environment and those stored as reserves in the cell 

 during times of plenty. 



Although there are several special branches and one known alter- 

 nate route, our attention will be focused for the present on the path- 

 way believed to be the primary sequence in plants and animals. These 

 reactions (Figure 7-1) are collectively called glycolysis from their role 

 in the metabolism of glycogen. The known ramifications of glycolysis 

 are indicated here by arrows and are summarized later (see pages 214 

 to 223). Most of these connections require more than one step. Arrows 

 with points at both ends signify that the process is known to be reversi- 

 ble and the actual direction depends upon the supply and demand of 



