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Groups repel one another charge phosphate

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Unformatted text preview: coupling exergonic rxns to endergonic rxns •  Energy usage in cell –  ⅓ used to move molecules across cell membrane –  chemical rxns. –  mechanical work 3 NH2 • Ex. How does a cell build Endergonic rxn a.a.’s, which requires energy NH3 Glu Glu ∆G = +3.4 kcal/mol + • ↑Endergonic coupled to Glutamic Ammonia Glutamine acid non- essenBal a.a. exergonic ATP phosphorylaBon • ATP gives up 1 phosphate, P ATP Glu releases energy + + ADP Glu • ATP phosphorylaBon NH (destabilizes) P NH Glu Glu • Net is exergonic, + + P • entropy _____. (b) Coupled with ATP hydrolysis, an exergonic reacBon 2 3 i Fig. 8- 10 (c) Overall free- energy change ATP: a renewable resource •  ATP regenerated by adding phosphate group to ADP •  energy comes from catabolic rxns (e.g. breakdown of sugar molecules) •  ~90kg (=__ lbs.) of ATP used daily (fortunately, recycled) ATP Energy from catabolism (exergonic, energy-releasing processes) + H 2O ADP + P Energy for cellular work (endergonic, energy-consuming processes) i Fig. 8-12 8.4: Enzymes are catalysts- speed up metabolic rxns •  Split, combine or rearrange molecules •  Catalyst- speeds up rxn w/o being consumed –  Enzymes: catalyBc proteins –  Specific (facilitates 1 type rxn.) •  Example: hydrolysis of sucrose (table sugar) by sucrase Sucrose (C12H22O11) Sucrase Glucose (C6H12O6) Fig. 8- 13 Fructose (C6H12O6) http://nutrition.jbpub.com/resources/animations.cfm?id=13&debug=0 4 Enzyme acBve site: where rxn takes place • Substrate (ex.__ ) binds to the acAve site of enzyme Substrate • AcBve site lowers EA barrier by – Holding substrate in place so H2O may break/join covalent bond of substrate – “Induced fit” – enzyme flexes to fit substrate AcAve site (a) 6 AcBve site is available for two new substrate molecules. (b) Fig. 8- 17 1 Substrates enter acBve site; enzyme changes shape such that its acBve site enfolds the substrates (induced fit). Substrates Enzyme- substrate complex Enzyme 2 Substrates held in acBve site by weak interacBons, such as hydrogen bonds and ionic bonds. Enzyme- substrate complex 3 AcBve site can lower EA and speed up a reacBon. AnimaBon: How Enzymes Work Enzyme 5 Products are released. 4 Substrates are converted to products. Products Enzymes...
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