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 Active site: region on enzyme’s surface, binds substrate during the catalyzed rxn

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

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

3.6.3 Explain the effects on enzyme activity of temperature, pH, substrate concentration. 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 pepsin (blue); trypsin (red)

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)

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