. Biochemistry of plants and animals, an introduction. Biochemistry. 220 PLANT BIOCHEMISTRY Work with strawberries suggests that an entirely different mechanism may be operating, so a need for further work is obvious. Sucrose is one of the major end procUicts of photosyntlicsis and for this reason is cliosen as illustrating the formation of disaccharides. Two mechanisms are believed to operate, at least under some condi- Uridine diphospho- glucose or Uridine diphospho- glucose fructose-6- phosphate fructose CH2OH sucrose. CH2OPO3- OH HO H sucrose-6'-phosphate Sucrose-6'-phosphate sucrose + HOP
. Biochemistry of plants and animals, an introduction. Biochemistry. 220 PLANT BIOCHEMISTRY Work with strawberries suggests that an entirely different mechanism may be operating, so a need for further work is obvious. Sucrose is one of the major end procUicts of photosyntlicsis and for this reason is cliosen as illustrating the formation of disaccharides. Two mechanisms are believed to operate, at least under some condi- Uridine diphospho- glucose or Uridine diphospho- glucose fructose-6- phosphate fructose CH2OH sucrose. CH2OPO3- OH HO H sucrose-6'-phosphate Sucrose-6'-phosphate sucrose + HOPO3 tions. The uridine diphosphoglucose consumed in these reactions and that of page 219 is thought to form according to Uridine diphosphate + ATP -^ uridine triphosphate + ADP (UTP) UTP + Glucosc-1-phosphate —> O o uridine diphosphoglucose + O" —P—O—P—o- II I O OH pyrophosphate In this way the uridine diphosphoglucose is made available for further reaction at the expense of ATP. As indicated in the scheme for glycolysis (page 168), the poly- saccharides are formed from hexosephosphates. Phosphorylase cata- lyzes the attachment of glucosyl groups to polyglucose units. These latter materials appear necessary as starters since the enzyme does not form maltose. The energy needed for the acetal bond comes from the glucosephosphate bond. This process continues until the molecules grow into amylose. Amylopectin, the other component of starch, results from the action of 4,6-transglucosidase, which shifts some of the glucose units on the ends from position 4 to 6 and forms the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Mallette, M. Frank (Manney Frank), 1917-. New York, Wiley
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