1. An Introduction to Enzymes Ms. Day AP Biology
Basic Intro Video
Digestion and Enzymes Intro Video (more info)

2. ENZYMES Enzymes are catalytic proteins A catalyst
Is a chemical agent that speeds up a reaction without being consumed by 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  CO2 + 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. 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.

11. 20 Different Amino Acids
Proteins (ex: enzymes) are made up of amino acids sequences (orders)
Each amino acid has different functional groups (R groups)

12. R groups (side chains) = red
SOME ARE:
POLAR w/ Charges
(+ or -) HYDROPHILIC
POLAR with NO Charges
HYDROPHILIC
Non polar
HYDROPHOBIC

13.  Involves carboxyl and amino groups
PRIMARY STRUCTURE
 Involves carboxyl and amino groups
Makes covalent peptide bonds btw amino acids
Involves carboxyl and amino groups
(backbone atoms)
SECONDARY STRUCTURE
Makes hydrogen bonds btw carboxyl and amino groups
TERTIARY STRUCTURE
 Involves R groups
Makes hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic or Van Der Waals interactions btw available R groups
QUATERNARY STRUCTURE
 Involves R groups
Same as tertiary structure

14. https://www. youtube. com/watch
= REVIEW/TUTORIAL OF PROTEIN FOLDING

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

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

17. 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
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. What factors denature proteins?
Denaturation = take away (or lower) the function of protein
Usually disrupts the 2° and 3° levels pH
Salt concentration
Temperature

20. Let’s look at denaturation…
Using your protein modeling kit

21. Why does pH denature proteins?
pH = extra H+ or OH- ions
Extra + or – charges around protein
Active site is distorted/blocked  alters ionic bonds (+/- interactions) that help make 3D shape
Enzyme cannot catalyze reactions at all or as well +
H+ ( pH)  in acids
+ charges bind to – R groups in active site - + +

22. Why does SALT [ ] denature proteins?
REMEMBER: SALTS are IONIC COMPOUNDS!!! THEY HAVE +/- ions
Salts = extra + or – ions
Extra + or – charges around protein
R-groups/side chains of amino acids  distorted/blocked by affecting ionic bonding
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 (movement of atoms) changes with temperature
Atoms move differently  affects bonding patterns that hold the protein together
Slightly higher temperature  MORE molecular motion (more molecular collisions)  enzyme works faster
BUT…if temp rises too high, heat will denature  molecules move too fast and can’t bond
Cold temp’s SLOW DOWN or stop activity b/c molecular motion decrease

24. [Enzymes]
Denaturation and eggs = example of denaturation using heat

25. [SUBSTRATE] ALSO EFFECTS ENZYME ACTIVITY
If [ ] of enzyme is constant…
Low amt of substrate  limiting factor
If amt of substrate increases  RATE of enzyme activity also increases
BUT…LOTS of substrate  enzymes become saturated with substrate
If more substrate is added, enzyme rate of reaction DOESN’T increase
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
Remember: enzymes are organic molecules
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.
EXAMPLE: Hemoglobin binding oxygen (O2) in blood

32. Cooperativity