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BIOC13H3 (52)
Daman Bawa (12)
Lecture 4

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Biological Sciences
Daman Bawa

Key Concepts: The Pentose Phosphate Pathway  The pentose phosphate pathway takes place within the cytoplasm  Aka hexose monophosphate shunt or phosphogluconate pathway  Reduces two molecules of NADP to NADPH (nicotinamide adenine dinucleotide phosphate) for each glucose-6-phosphate that is oxidatively decarboxylated to ribulose-5-phosphate.  NADPH is functionally similar to NAD however, NADPH is the primary + reductant in the cell, whereas, NAD is the primary oxidant.  The PPP is also responsible for producing ribose-5-phosphate which provides the ribose sugar backbone that anchors the nucleotide base to DNA and RNA polymers Pentose Phosphate Pathway is critical for the cell  There are two main phases for PPP: o The oxidative phase generates NADPH which is required for many biosynthetic pathways and for detoxification of reactive oxygen species o The non-oxidative phase interconverts 3C, 4C, 5C, 6C and 7C monosaccharides to produce ribose-5-phosphate for nucleotide synthesis, and also to regenerate glucose-6-phosphate to maintain NADPH production by the oxidative phase. Net reaction:  Key Enzymes o Glucose-6-Phosphate Dehydrogenase (G6PD) - This is the first commited step in the pathway and is feedback-inhibited by NADPH. o Transketolase and Transaldolase - (converts ketose to aldose and aldose to ketose), together these two enzymes catalyze the reversible "carbon shuffle" reactions of the nonoxidative phase of the pathway  Pathways requiring NADPH include: o Synthesis  Fatty acid biosynthesis  Cholesterol biosynthesis  Neurotransmitter biosynthesis  Nucleotide biosynthesis o Detoxification  Reduction of oxidized glutathione (critical in RBC production)  Cytochrome P450 monooxygenases  Tissues with active PPPs. o Adrenal gland - steroid synthesis o Liver - fatty acid and cholesterol synthesis o Testes and Ovaries - steroid synthesis o Adipose tissue and Mammary gland - fatty acid synthesis o Red blood cells - maintenance of reduced glutathione Regulation of Pentose Phosphate Pathway  Glucose 6 Phosphate dehydrogenase is rate limiting  4 different metabolic scenarios govern how glycolysis and the pentose phosphate pathway are intertwined 1. Scenario where you need R5P in which you have a lot
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