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Of substrate induced t enzyme

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Unformatted text preview: catalyze rxns by lowering EA barrier •  AcAvaAon energy- required to iniBate rxn that would occur spontaneously….eventually (too slow for cell) •  Why is this good from a cell’s perspecBve ? •  Without EA, rxns would occur needed or not Free energy Course of reaction without enzyme EA without enzyme EA with enzyme is lower Reactants Course of reaction with enzyme ∆G is unaffected by enzyme Products Animation: How Enzymes Work Progress of the reaction Fig. 8- 15 5 •  general rule: rxn. rate doubles for every 10° C increase (w/in tolerable temp. range) Optimal temperature for Optimal temperature for typical human enzyme enzyme of thermophilic (heat-tolerant) bacteria 40 0 60 20 80 Temperature (ºC) (a) Optimal temperature for two enzymes Optimal pH for pepsin (stomach enzyme) Rate of reaction •  Enzymes have different opBmal temps & pH Rate of reaction Environmental factors influence enzyme acBvity 100 Optimal pH for trypsin (intestinal enzyme) 4 5 6 0 1 2 3 pH (b) Optimal pH for two enzymes 7 8 9 10 Lactase & acBvaBon energy EA •  Lactase binds lactose (high specificity) •  Molecule oriented in acBve site, bonds split •  No/low lactase producBon- lactose intolerant; common in adults of various ethnic groups (30 mil Americans) GeneBc disorders of enzyme deficiency •  Lactose intolerance trivial compared to other enzyme deficiencies –  Tay- Sachs: enzyme to break down lipids not made; fatal buildup in nerve cells –  Phenylketoneuria (PKU) “PHENYLKETONURICS: CONTAINS PHENYLALANINE” •  Body lacks enzyme to metabolize; control w/diet •  [inheritance studied in later chapters] Tested for at birth 6 Many enzymes require cofactors (non- protein enzyme “helpers”) to be acBve •  essenBal to health •  Organic: vitamins (e.g. Vit C, B1) & non- vitamins (ATP, heme) •  Inorganic: minerals (e.g. Iron, Zinc) 8.5: Cells regulate metabolism by regulaBng enzymes •  Switch genes on/off that encode specific enzymes •  Regulate by acBvaBng or inhibiBng enzymes: –  feedback inhibiBon, non/compeBBve inhibiBon, allosteric acBvaBon & inhibiBon –  some inhibitors may cause death: cyanide, sarin gas, warfarin (=Coumadin) Fig. 8- 19 Substrate Active site Competitive inhibitor Enzyme Noncompetitive inhibitor (a) Normal binding (b) Competitive inhibition (c) Noncompetitive inhibition Feedback InhibiBon •  Final product blocks enzyme from engaging substrate enzyme 2 enzyme 1 SUBSTRATE enzyme 3 enzyme 4 enzyme 5 A cellular change, caused by a specific acBvity, shuts down the acBvity that brought it about END PRODUCT (tryptophan) 7...
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