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IB Topic 3

Enzymes are globular proteins that act as biological catalysts, accelerating specific chemical reactions by enabling faster equilibrium. Their activity is highly specific, facilitated by an active site that binds substrates, illustrated by models like the lock-and-key and induced-fit. Factors such as temperature, pH, and substrate concentration greatly influence enzyme activity, with optimal conditions varying for different enzymes. Denaturation can permanently alter an enzyme’s structure, affecting its function. Additionally, lactase is vital in producing lactose-free milk, catering to lactose-intolerant individuals.

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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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