ib topic 3
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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 - PowerPoint PPT PresentationTRANSCRIPT
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IB Topic 3The Chemistry of Life
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3.6Enzymes
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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
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3.6.2 Explain enzyme-substrate specificity.
• Lock & key model– Substrate fits into
active site of enzymeFructose-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
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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
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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)
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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)
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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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