1. Enzymes
Protein catalysts- can accelerate reaction rates as much as 1017 – typical acceleration is 107/108 over uncatalyzed reactions
Responsible regulating the rate of virtually all important chemical reactions in the cell (RNA can also catalyze splicing reactions)
Highly specific – can distinguish between stereoisomer substrates; typically catalyze 1 reaction in the cell

2. Figure 6.15 The catalytic cycle of an enzyme

3. Models of Enzyme Action
LOCK AND KEY
INDUCED FIT
Enzyme structure is rigid.
Substrate is exact complement to active site shape of enzyme
Enzyme structure changes upon binding of substrate
Enzyme structure is flexible- currently accepted model.
Enzyme binds substrate loosely, transition state tightly

4. Conformational changes in yeast hexokinase on binding glucose.

5. Figure 6.13 Enzymes lower the barrier of activation energy

6. How do Enzymes catalyze reactions?

7. Lactase Example of Biotechnology
Lactase – enzyme that breaks down lactose (disaccharide) into Monosaccarides galactose and glucose
Uses:
Milk/dairy products for lactose intolerant people
Use in milk/shakes or yogurt (galactose/glucose are sweeter and ice cream (lactose gives gritty texture when frozen.
Bacteria ferment glucose and galactose more quickly than lactose reduces production time for yogurt and cottage cheese.

8. Factors that Affect the Rates of Enzyme catalyzed Reactions
[Enzyme] - ↑ [E], ↑ rate
[Substrate]- ↑ [S], ↑ rate only up to a point
pH – optimal range
Temperature- optimal range
Inhibitors (↓) or activators (↑)

9. Enzyme Saturation

10. At low [S] concentrations, active sites are available; at high [S] are active sites are occupied, rate is limited by availability of enzyme

11. Figure 6.16 Environmental factors affecting enzyme activity

12. Effect of high temperature
↑Temperature → ↑ average KE (energy of motion) of atoms
Distance between weakly attracted atoms in side chain ↑ → bonds break

13. Effect of Low Temperature
Molecules move slowly, % of reactant substrate molecules with enough energy to overcome Ea ↓
Also, enzyme generally needs to be able adjust conformation upon binding of substrate(induced fit); lower KE could impact flexibility of enzyme ↓ catalytic efficiency

14. Effect of Changing pH Lower pH → ↑ [H+] → side chains become more +
Higher pH → [H+] ↓ → side chains become more –
Salt bridge and H-bonds disrupted

15. Figure 6.17 Inhibition of enzyme activity

16. Figure 6.19 Feedback inhibition