1. An Introduction to Enzymes Ms. Gaynor AP Biology

2. ENZYMES Enzymes are catalytic proteins A catalyst
Is a chemical agent that speeds up a reaction without being consumed by the reaction

3. Chemical Reaction Every chemical reaction between molecules
Involves both bond breaking and bond forming
Figure 8.13
H2O H HO OH O
CH2OH
Sucrase
Sucrose
Glucose
Fructose
C12H22O11
C6H12O6 +

4. Catabolic vs. Anabolic Reactions
CATABOLIC (an exergonic reaction)
Reactions that BREAK down LARGE molecules into smaller ones
Think: “C” for cut apart (make smaller)
RELEASE ENERGY
POLYMER  MONOMER
Ex: Cellular Respiration (glucose  O2 + ATP)
ANABOLIC (an endogonic reaction)
Reactions that PUT TOGETHER down SMALL molecules into LARGER ones
Think: “A” for add together (make bigger)
ABSORBS/NEEDS ENERGY
MONOMER  POLYMER
Ex: Photosynthesis (sun + CO2 + H2O  Glucose)

5. EXERGONIC vs. ENDERGONIC
Exergonic reaction
RELEASE ENERGY (exits)
Do NOT need extra energy  occurs spontaneously
OCCUR SLOWLY!!!
Endogonic reaction
ABSORBS/NEEDS ENERGY (INTO)
Will NOT happen without ENERGY input
NOT SPONTANEOUS!

6. Activation Energy, EA
initial (starting) amount of energy needed to start a chemical reaction
Amount of energy needed to “PUSH” reactants over a barrier
Determines the RATE of the reaction
Proportional to difficulty of breaking bonds
All reactions require energy of activation (EA)
ENZYMES
Lowers the EA barrier so that chemical reactions can more quickly.

7. The energy profile for a reaction (net release of energy)
Uphill= EA required to start reaction.
Downhill = the loss of energy by molecules in reaction.
DG is the difference in energy of products and reactants.
The energy profile for a reaction (net release of energy)
Free energy
Progress of the reaction
∆G < O EA A B C D
Reactants
Transition state
Products

8. Unaffected by enzyme

9. Substrate Specificity of Enzymes
The substrate
Is the reactant an enzyme acts on
The enzyme
Binds to its substrate, forming an enzyme-substrate complex

10. NOTE: Oxygen gas(O2) forms BUBBLES
ENZYME
SUBSTRATE (REACTANT)
PRODUCTS

11. Most enzyme-substrate interactions  result of weak bonds.
The active site
Is the region on the enzyme where the substrate binds
Figure 8.16
Substrate
Active site
Enzyme
(a)
Most enzyme-substrate interactions  result of weak bonds.

12. 20 Different Amino Acids
Proteins (ex: enzymes) are made up of amino acids sequences (orders)
Each amino acid has different functional groups (R groups)

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

15.  Involves carboxyl and amino groups
Makes covalent peptide bonds btw amino acids
 Involves carboxyl and amino groups
Makes hydrogen bonds btw carboxyl and amino groups
 Involves R groups
Makes hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic or Van Der Waals interactions btw available R groups
 Involves R groups
Same as tertiary structure

16. Induced fit of a substrate
“tight” fit  creates a “microenvironment”
Enzyme binds to substrate better using amino acid R groups
Weakens bonds  gets to transition state faster
Figure 8.16
(b)
Enzyme- substrate
complex

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

18. 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

19. (b) Optimal pH for two enzymes
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

20. What factors denature proteins?
Denaturation = take away (or lower) the function of protein pH
Salt concentration
Temperature

21. Why does pH denature proteins?
In either excess H+ or excess OH- ions, protein's shape is altered
Active site is distorted/blocked  alters ionic bonds that contribute to its functional shape
Enzyme cannot catalyze reactions at all or as well +
H+ ( pH)  in acids -
+/-
+/-

22. Why does SALT [ ] denature proteins?
REMEMBER: SALTS are IONIC COMPOUNDS!!! THEY HAVE +/- ions
In either excess + or excess - ions, protein's shape is altered
R-groups/side chains of amino acids  distorted/blocked by affecting ionic bonding
Enzyme cannot catalyze reactions at b/c it forms a precipice
Less salt= R groups form extra bonds with each other
More salt= disrupt R groups from normal bonding patterns

23. Why does TEMPERATURE denature proteins?
Kinetic energy changes with temperature
Atoms move differently and affects the bonding patterns that hold the protein together
A higher temperature generally results in increase activity b/c molecular motion increases resulting in more molecular collisions
If, however, temp rises above a certain point, the heat will denature  molecules move too fast and can’t H-bond
Cold temp’s SLOW DOWN or stop activityb/c molecular motion decrease

24. [Enzymes]
Denaturation and eggs

25. [SUBSTRATE] ALSO EFFECTS ENZYME ACTIVITY
If [ ] of enzyme is constant…
at lower [substrate]  [substrate]= limiting factor
As [substrate] increases, RATE of enzyme activity also increases
However, at very high [substrate]  enzymes become saturated with substrate and a higher concentration of substrate does NOTHING to increase the reaction rate
All the enzymes are already in use

26. Cofactors Cofactors Are non-protein enzyme helpers
Bind to active site to enhance enzymatic rxns
Cofactors may be inorganic metals such as zinc, iron, or copper.
Coenzymes
Are organic cofactors
Coenzymes example= vitamins

27. Enzyme Inhibition Competitive inhibitors Non-competitive inhibitors
mimic the substrate and compete for the active site.
Non-competitive inhibitors
bind to the enzyme away from the active site, and indirectly cause a change in the active site (i.e.-changing the function)

28. Enzyme Inhibitors

29. Allosteric Enzymes A specific type of enzyme
A specific type of enzyme
Helps regulate cell processes
Can change their conformational shape
Have 2 states (ACTIVE vs. INACTIVE)

30. Allosteric Enzymes

31. Stabilized active form
Cooperativity
Is a form of allosteric regulation that can amplify enzyme activity
Figure 8.20
Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation.
Substrate
Inactive form
Stabilized active form
(b) Cooperativity: another type of allosteric activation. Note that the inactive form shown on the left oscillates back and forth with the active form when the active form is not stabilized by substrate.

32. Cooperativity