1. Enzymes
Lecture #8

2. Chemical Reactions Every chemical reaction
Involves both bond breaking and bond forming
Initial amount of energy to start reaction = activation energy (EA)
REACTANTS
PRODUCTS
Figure 8.13
H2O H HO OH O
CH2OH
Sucrase
Sucrose
Glucose
Fructose
C12H22O11
C6H12O6 +

3. What is an ENZYME? Enzymes are proteins Also known as a catalyst
speeds up a chemical reaction
Lower the amount of energy needed to start a reaction

4. Enzymes Are specific for what they will catalyze Are Reusable
End in –ase
-Sucrase
-Lactase
-Maltase

5. How do enzymes Work?
Enzymes work by weakening bonds which lowers activation energy

6. ENZYMES LOWERS THE AMOUNT OF ACTIVATION ENERGY NEEDED  INCREASES SPEED OF REACTION

7. Progress of the reaction
Transition state = bonds in substrates (reactants) are WEAKENED and about to break
Free energy
Progress of the reaction
∆G < O EA A B C D
Reactants
Transition state
Products
Enzymes help “weaken” bonds FASTER  TRANSITION STATE REACHED FASTER!!!

8. Enzyme Vocabulary The substrate Is the reactant an enzyme acts on
The enzyme
binds to its substrate, forming an enzyme-substrate complex
Enzyme
Substrate
Joins

9. Is the region on the enzyme where the substrate binds
The active site
Is the region on the enzyme where the substrate binds
Enzyme
Substrate
Active Site C B

10. Substrate Active site Enzyme
Figure 8.16
Substrate
Active site
Enzyme
(a)

11. Induced fit of a substrate
“tight” fit  helps weaken bonds FASTER in substrate(s)
Weakens bonds  gets to transition state faster

13. Remember…
Proteins (ex: enzymes) are made up of DIFFERENT amino acids sequences (orders)
Each amino acid has different functional groups (R groups)
Different R groups in active site allow enzyme to bind different substrates

14. R groups = red POLAR w/ Charges (+ or -) HYDROPHILIC
POLAR with NO Charges
HYDROPHILIC
Non polar
HYDROPHOBIC

15. Enzyme is RECYCLED!!Never used up or destroyed

16. What Affects Enzyme Activity?
Two factors:
1. Environmental Conditions
2. Enzyme Inhibitors

17. EFFECTS OF TEMPERATURE & pH
1. Environmental Conditions
EFFECTS OF TEMPERATURE & pH
Enzymes have an optimal temperature and pH in which it can function
Figure 8.18
Optimal temperature for
enzyme of thermophilic
Rate of reaction 20 40 80
100
Temperature (Cº)
(a) Optimal temperature for two enzymes
typical human enzyme
(heat-tolerant)
bacteria

18. (b) Optimal pH for two enzymes
1. Environmental Conditions
Enzymes have an optimal pH in which it can function
Figure 8.18
Rate of reaction
(b) Optimal pH for two enzymes
Optimal pH for pepsin
(stomach enzyme)
Optimal pH
for trypsin
(intestinal
enzyme) 1 2 3 4 5 6 7 8 9

19. Denaturation = take away (or lower) the function of protein
1. Environmental Conditions
What can destroy enzymes?
Denaturation = take away (or lower) the function of protein pH
Salt concentration
Temperature

20. Why does pH denature proteins?
Excess H+ or excess OH- ions, protein's shape is altered
Active site is blocked  enzyme CAN’T bind its substrate
Enzyme cannot complete reactions at all or as well H+ H+ H+

21. Why do salts denature proteins?
Excess + or - ions, protein's shape is altered…
remember salts are made of ions bonded together!
Active site is blocked  enzyme CAN’T bind its substrate
Enzyme cannot complete reactions at all or as well
Na+
Na+
Cl+

22. Why does TEMPERATURE denature proteins?
Kinetic energy (energy of motion) changes
Atoms move differently and bonding in protein is disrupted
Higher temperatures = more movement/kinetic energy
Atoms in protein move too fast and can’t bond together (ACTIVE SITE IS DESTROYED!)
Cold temp’s SLOW DOWN or stop activity because molecular motion decrease

23. Two examples of Enzyme Inhibitors:
Competitive Inhibitors
Noncompetitive Inhibitors

24. 2. Enzyme Inhibitors
a. Competitive inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site.
Enzyme
Substrate
Competitive inhibitor

25. 2. Enzyme Inhibitors b. Noncompetitive inhibitors:
do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site.
Enzyme
Substrate
Noncompetitive
Inhibitor
active site
altered

26. Enzyme Inhibitors Ex: Poison/toxins or drugs Competitive inhibitor
Noncompetitive inhibitor
Enzyme Inhibitors
Ex: Poison/toxins or drugs

27. Let’s Practice…
Products
Substrate (reactant)
Active site
Enzyme

28. Let’s Practice…True/False
_______ Enzymes interact with specific substrates
_______ Enzymes speed up reactions
_______ Boiling temperature will increase the rate of reaction
______ Enzymes increase activation energy
_______ Changing the pH will not change the rate of reaction
_______ Freezing an enzyme will decrease the rate of reaction
True
True
False
False
False
True