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19 Cards in this Set
- Front
- Back
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What is Metabolism?
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The sum total of chemical reactions occurring in cells.
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What are the major divisions of Metabolism?
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- Catabolism: energy yielding (ATP yielding) conversion of fuels to end products
- Anabolism: energy requiring (ATP requiring) bio synthetic processes |
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Glycolytic Pathway
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- Energy generating pathway involving the conversion of glucose, or some other sugar, to pyruvate
- Occurs in cytosol - Enzymes are soluble - Generates 2 ATP for each glucose converted to 2 pyruvate - Redox agents are 2 NAD+ to NADH + H+ |
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Glycolysis Step 1
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Hexokinase Reaction
- Glucose + ATP to Glucose 6-phosphate + ADP - Irreversible - Regulated by Hexokinase - Once Glu 6-P is formed, it cannot exit cell, because phosphorylated compounds are generally membrane- impermeable - Once G6P is formed, all intermediates in pathway are also phosphorylated and trapped in cell |
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Hexokinase
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- An allosteric enzyme inhibited by its product, Glu 6-P
- Found in most cells |
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Glucokinase
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- Specialized hexokinase found in the liver
- Suited to liver's role as chief feeder of other tissues in the body - Kinetic properties are suited to the fact that blood arriving in the liver from the intestines will have widely varying glucose concentrations, depending upon dietary state - See slide for Kinetic Properties of HK and GK |
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Glycolysis Step 2
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Phosphoglucoisomerase (PGI) Reaction
- Glu 6-P = Fructose 6-P - Regulated by PGI - Reversible - A Moonlighting protein: catalyzes inside of cell, nerve growth factor outside of cell |
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Glycolysis Step 3
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Phosphofructokinase 1 (PFK-1) Rxn
- Fru 6-P + ATP to Fru 1,6 Bisphosphate + ADP - Reg by PFK- 1 - Irreversible - Most IMPORTANT (step) control point in glycolytic pathway - ATP inhibits - AMP and Fru 2,6 BP activate - Enzyme has 2 binding sites for ATP, one a substrate-binding site and the other allosteric. |
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Allosteric Inhibition and Activation (ATP & F 2,6 BP)
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ATP:
(-) : Allosteric Inhibitor (+): Allosteric Activator * In Low concentrations, ATP is a substrate. In High concentrations, ATP is an allosteric inhibitor F 2,6 BP: (-): Allosteric inhibitor (+): Allosteric activator |
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Glycolysis Step 4
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Fructose Bisphosphate Aldolase
- Fru 1,6 BisP = Glyceraldehyde 3-P + Dihydroxyacetone P - Top half of hexose becomes DHAP and the bottom becomes Glycer 3P (see lecture notes) - Reaction occurs in cells even with deltaGknot'= +23.9kj/mol |
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Glycolysis Step 5
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Triose Phosphate Isomerase
- This step interconverts th two triose phosphates: Glycer3P = DHAP - Since only Glycer3P has a further fate in glycolytic pathway, it is as if 2 Glycer3P are produced per molecule of glucose |
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Glycolysis Step 6
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Glyceraldehyde Phosphate Dehydrogenase
- Glycer3P + NAD+ + Pi = 1,3 BPG + NADH + H+ - 2 NAD+ is reduced per 1 glucose - The phosphate at position 1 is a phosphoanhydride and has a free energy of hydrolysis - The phosphate at position 3 is a phosphoester and has a low free energy of hydrolysis - The enzyme is inactivated by iodoacetate, implying that a Cys-SH is necessary for activity. |
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Glycolysis Step 10
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Pyruvate Kinase
- PEP + ADP to Pyruvate + ATP - Irreversible and regulatory - Allosteric activator: F1,6BP, an example of feed-forward activation - Allosteric inhibitor: ATP - A net of 2 ATP produced in this step from glucose |
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Anaerobic Fate of Pyruvate
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Lactate Dehydrogenase
- Pyruvate + NADH + H+ = Lactate + NAD+ - When Oxygen is in short supply in tissues like voluntary skelatal muscle under conditions of rigorous exercise, lactate, rather than pyruvate, is the end product of glycolysis - The function of this terminal step is to regenerate NAD+ for the Glycer3P dehydrogenase reaction (or re-oxidize NADH for step 6) - See slide for picture |
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Glycolysis Step 7
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Phosphoglycerate Kinase
- 1,3 BPG + ADP = 3-PGA + ATP - The high energy phosphate at position 1, the phosphoanhydride, can be transferred to ADP to generate an ATP |
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Glycolysis Step 8
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Phophoglycerate Mutase
- 3-PGA = 2-PGA |
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Glycolysis Step 9
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Enolase
- 2-PGA = PEP - PEP is phosphoenolpyruvate. It is a high energy phosphate compound |
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Glycolysis Net Reaction
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- Total of 4 ATP is generated
- 2 used to phosphorylate glucose and F6P - Net ATP yield is 2 - Glucose + 2 ADP + 2Pi = 2 Lactate + 2 ATP + 2 H2O |
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Labeling Relationships
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- Carboxyl group of lactate comes from C3 and C4 of glucose
- Middle carbon atom of lactate come from C2 and C5 - Methyl carbon atom comes from C1 and C6 - See lecture for illustration |
