Understanding the Role of Transketolase and Transaldolase in Sugar Metabolism

The nonoxidative phase of the pentose phosphate pathway (PPP) metabolizes ribulose 5-phosphate produced in the oxidative phase. Two enzymes that play an important role in this metabolism are transketolase and transaldolase. Which of following statements CORRECTLY describes the reactions catalyzed by transketolase and transaldolase?a. These enzymes react with phosphorylated five-carbon sugars to generate ATP. b. These enzymes are used to generate NADPH.c. These enzymes catalyze two-carbon transfers and the joining of different sugarmolecules.d. These enzymes catalyze one-carbon transfers and the joining of different sugar molecules.e. These enzymes are important for interconverting ribulose, ribose and xyulose.

c. These enzymes catalyze two-carbon transfers and the joining of different sugarmolecules.

c. These enzymes catalyze two-carbon transfers and the joining of different sugar molecules.

Transketolase plays a role in the transfer of two-carbon units from a ketose sugar donor, such as xylulose-5-phosphate or sedoheptulose-7-phosphate, to an aldose acceptor sugar, such as glyceraldehyde-3-phosphate or erythrose-4-phosphate. In this process, transketolase transfers a two-carbon fragment of the donor sugar to the acceptor sugar.

Transaldolase, on the other hand, catalyzes the transfer of a three-carbon unit, often dihydroxyacetone, from a ketose donor to an aldose acceptor. This transfer involves cleavage of a six-carbon sugar into a three-carbon and a four-carbon fragment, followed by the transfer of the three-carbon fragment to the acceptor sugar.

Both of these reactions are important for the interconversion of different sugar molecules and the production of intermediates needed for various metabolic pathways. They are not involved in generating ATP or NADPH.

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