Pentose pathway, non-oxidative branch (Saccharomyces cerevisiae)

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The reactions of the non-oxidative branch of the pentose phosphate pathway are reversible and are important for generating ribose-5-phosphate, which is required for the biosynthesis of several biomolecules, including RNA and DNA. The flow of glucose 6-phosphate through glycolysis and the pentose phosphate pathway is linked through two enzymes of the non-oxidative branch of the pentose phosphate pathway, transketolase (Tkl1p and Tkl2p) and transaldolase (Tal1p). The ability of these enzymes to convert one type of sugar into another allows them to convert the byproduct of one pathway into the substrate of another pathway in order to meet the metabolic needs of the cell. For example, if the cell needs ribose 5-phosphate, glyceraldehyde 3-phosphate and fructose 6-phosphate will be converted to ribose 5-phosphate. If the cell needs NADPH or ATP more than ribose 5-phosphate, ribose 5-phosphate will be converted to glyceraldehyde 3-phosphate and fructose 6-phosphate for use by the oxidative branch of the pentose phosphate pathway or glycolysis, respectively.