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IB Topic 3

IB Topic 3. The Chemistry of Life. 3.6. Enzymes. 3.6.1 Define enzyme & active site. Enzyme : globular protein, accelerates a specific chemical reaction by reaching rxn’s equilibrium faster (biological catalyst) Recycled over and over again

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IB Topic 3

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  1. IB Topic 3 The Chemistry of Life

  2. 3.6 Enzymes

  3. 3.6.1 Define enzyme & active site. • Enzyme: globular protein, accelerates a specific chemical reaction by reaching rxn’s equilibrium faster (biological catalyst) • Recycled over and over again • Active site: region on enzyme’s surface, binds substrate during the catalyzed rxn

  4. 3.6.2 Explain enzyme-substrate specificity. • Lock & key model • Substrate fits into active site of enzyme Fructose-6-phosphate + phosphate ---phosphofructokinase  fructose-1,6-diphosphate • 3D structure • Protein! Active site shape is specific to substrate’s shape....1,2,3,4,structure of prtn. • Induced-fit model • Affinity for substrate(s), conformational change, see 7.6

  5. 3.6.3 Explain the effects on enzyme activity of temperature, pH, substrate concentration. • Enzyme activity: how fast substrate disappears –or– how quick product is formed • Temperature • temp increase  KE increases, more collisions, rxn rate increases • optimal temp = highest rxn rate • higher temp: KE too high, bonds break, active site changes • Optimum temp humans ~37°C • Denature above 60°C • Thermophilic bacteria up to 80°C

  6. 3.6.3 Explain the effects on enzyme activity of temperature, pH, substrate concentration. pepsin (blue); trypsin (red) • pH • >/< optimal: bonds break • Pepsin (stomach) optimum pH = 2 • Trypsin (sm intestine) optimum pH = 8 • Substrate concentration • More concentrated  faster (toothpickase activity!) • # active sites occupied increases, competition for a.s. • rate constant when a.s. fully saturated

  7. 3.6.4 Define denaturation. • structural change in protein, • results in loss (usually permanent) of its biological properties • Struct chg in active site  loses function • High temps, extreme pH • Raw egg: several proteins • (cook = denatured, can’t go back to raw state)

  8. 3.6.5 Explain the use of lactase in the production of lactose-free milk. • Common! ~70% adult humans worldwide • Genetic basis: • 2% of Swedes • 75% of African Americans • Almost 100% of American Indians • Lose ability to produce lactase in early childhood • Effects: diarrhea, gas if consume lots dairy • Attach lactase to a large molecule, bring in contact with milk

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