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[NADH]/[NAD+]
[NADPH]/[NADP+] |
-usually 10^-4 in cytosol to oxidize metabolites
-usually 100 in cytosol to favor reductive biosynthesis |
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mcs5109 Wed, 03 Feb 2010 07:28:01 GMT |
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| NADH vs. NADPH |
-not metabolically interchangeable
-many endergonic rxns (mostly reductive biosynthesis of fatty acids, cholesterol, and photosynthesis) require NADPH
-NADPH is ultimate e- source for reduction of ribonucleotides to deoxyribonucleotides for DNA synthesis |
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mcs5109 Wed, 03 Feb 2010 07:28:01 GMT |
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| primary functions of the pentose phosphate pathway |
1. to provide NADPH
2. to provide ribose-5-phosphate for nucleotide biosynthesis
3. to metabolize dietary pentoses (from digestion of nucleic acids)
-operates exclusively in cytosol
-tissues heavily involved with fatty acid synthesis and cholesterol synthesis are rich in this pathway |
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mcs5109 Wed, 03 Feb 2010 07:33:27 GMT |
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| Why regulate glycolysis and gluconeogenesis at >1 point? |
1. many other pathways interconnect with glycolysis
2. glycolytic intermediates are precursors for other biosynthetic pathways; the regulatory needs are too complicated to be served in a single rate-limiting step |
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mcs5109 Wed, 03 Feb 2010 07:02:16 GMT |
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| regulation of glycolysis and gluconeogenesis |
-controlled at points in pathway where forward and reverse rxns can be independently regulated
-control of flux thru any pathway requires that the flow thru the rate-limiting step varies in response to metabolic requirements
-ex: if E needs high, glycolysis increases and gluconeogenesis decreases |
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mcs5109 Wed, 03 Feb 2010 06:53:33 GMT |
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| 3 bypass steps in gluconeogenesis |
1. pyruvate carboxylase; PEP carboxykinase (PEPCK)
2. fructose 1,6 biphosphatase
2. glucose-6-phosphatase |
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mcs5109 Wed, 03 Feb 2010 05:30:18 GMT |
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| Why opposing metabolic pathways are never just the reverse of each other |
1. both forward and reverse rxns must each be energetically favorable under the same physiological conditions
2. the pathways must be independently controllable so that one direction can be activated while the other is inhibited
-if the rxns of the two pathways were just reversible and catalyzed by the same enzymes, the flow of carbon would be dictated by mass action, not by the cell's changing E needs |
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mcs5109 Fri, 29 Jan 2010 03:19:55 GMT |
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| What's the physiological significance of gluconeogenesis? |
-gluconeogenesis occurs in the liver (and to a lesser extent in the kidneys) and provides glucose to cells such as brain, RBCs, and CNS
-energy source
-the brain and RNCs almost completely dependent on glucose for E
-when fasting, the body's E needs met by gluconeogenesis |
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mcs5109 Fri, 29 Jan 2010 03:01:01 GMT |
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| non-carb precursors for gluconeogenesis |
-lactate
-pyruvate
-glycerol
-aas
-TCA cycle ints |
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mcs5109 Fri, 29 Jan 2010 02:54:10 GMT |
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