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Unformatted text preview: Pentose Phosphate Pathway Jonathan Galazka 3/8/2009 What?‐ The pentose phosphate pathway has two phases: 1. In the oxidative phase (page 39 in reader), the pathway produces reducing power in the form of NADPH, and pentose (5 carbons) carbohydrates in the form of ribose 5‐phosphate from glucose 6‐phosphate. Glucose 6‐phosphate + 2NADP+ + H2O ‐‐‐> ribose 5‐phosphate + CO2 + 2NADPH + 2H+ 2. The nonoxidative phase (page 38 in reader) occurs when NADPH, but not ribose 5‐ phosphate is required. In this case, the 5‐carbon sugars produced in the oxidative phase are recycled into 6‐carbon sugars. These 6‐carbon sugars are converted to glucose 6‐phophate. The glucose 6‐phosphate is then used by the oxidative phase to produce more NADPH. Where? – For most organisms it takes place in the cytosol. In plants, most steps take place in chloroplasts. When? – Occurs when an organism requires ribose for nucleotides such as DNA and RNA or when the reductive power of NADPH is needed. NADPH is important for the neutralization of reactive oxygen species and the biosynthesis of fatty acids. Who? – The enzymes that catalyze the oxidative phase are given on page 39 of your reader. The enzymes that catalyze the non‐oxidative branch are given on page 41 of your reader. Why? – The pentose phosphate pathway has two important functions. First, it produces the 5‐carbon sugar, ribose 5‐phosphate. Ribose is a component of deoxyribonucleic acid, better known as DNA. Second, it produced NADPH. The reducing power of NADPH is essential for the building certain biomolecules such as fatty acids. The reducing power of NADPH is also critical in the neutralization of reactive oxygen species such as hydrogen peroxide. Hydrogen peroxide is neutralized by an enzyme that consumes reduced glutathione (GSH) and produces oxidized glutathione (GSSG) (Page 39 in your reader). ...
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- Spring '09