IB Topic 3The Chemistry of Life

3.6Enzymes

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 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

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