1. Proteins as Enzymes

2. 1. Enzymes are proteins that that carry out most catalysis in living organisms
2. Unique three-dimensional shape enables an enzyme to stabilize a temporary association between substrates. The substrate fits into a specific place on the enzyme called an active site.
3. Because the enzyme itself is not changed or consumed in the reaction, only a small amount is needed, and can then be reused.
4. One Enzyme, one reaction. Enzymes are specific to the substrate.

3. 5. Enzymes have specific names
a. end in “ase”.
b. Named according to the substrate they
act on.
c. Named according to the type of
reaction they catalyze.
Ex: DNA Ploymerase or Lipase

4. Enzymes Are Biological Catalysts
catalyst –substance that lowers the activation energy, reactions proceed to products at a faster rate.
Activation energy- refers to the extra energy required to destabilize existing chemical bonds and initiate a chemical reaction.

5. Energy supplied Activation energy Reactant Energy released Product
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Energy supplied
Activation
energy
Reactant
Energy released
Product

6. Uncatalyzed Catalyzed Activation energy Reactant Product
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Uncatalyzed
Catalyzed
Activation
energy
Reactant
Product

7. Enzyme Structure
Most enzymes are quaternary with one or more active sites.
Substrates bind to the enzyme at these active sites, forming an enzyme-substrate complex.
With this binding, there is a slight change in shape of the complex, allowing close bonding and reactions to occur=

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Active site
Enzyme

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Substrate

10. substrate complex. Products are Enzyme The substrate,
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The substrate,
sucrose, consists
of glucose and
fructose bonded
together. 1 2
The substrate
binds to the
enzyme, forming
an enzyme-
substrate
complex.
Glucose
Fructose
Bond 4
Products are
released, and
the enzyme is
free to bind
other
substrates.
H2O
Active site 3
The binding of
the substrate
and enzyme
places stress on
the glucose-
fructose bond,
and the bond
breaks.
Enzyme

11. Lego Enzymes

12. R1 B1 BL1 R3 G1 L1 Amino Acids B2 R2 W1 W2 W4 W3 substrate Active site
Enzyme

13. Enzyme Forms
A multi-enzyme complex is composed of several enzymes, catalyzing the different steps of a sequence of reactions, that are associated with one another.
subunits work in concert, providing significant advantages in catalytic efficiency

14. Substrate
Enzyme 1
Enzyme 2
Enzyme 3
Enzyme 4
Product

15. Factors Affecting Enzyme Activity
Temperature
Rate of an enzyme-catalyzed reaction increases with temperature, but only up to an optimum temperature or the enzyme denatures. Too low and the reaction is slowed down.

16. hotsprings prokaryote
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Optimum
temperature for
human enzyme
Optimum temperature
for enzyme from
hotsprings prokaryote
Rate of reaction 30 40 50 60 70 80
Temperature of reaction (°C)

17. pH
Interactions hold enzymes together. If the pH is too high or too low they will be denatured.

18. Optimum pH for pepsin Optimum pH for trypsin Rate of reaction 1 2 3 4
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Optimum pH
for pepsin
Optimum pH
for trypsin
Rate of reaction 1 2 3 4 5 6 7 8 9
pH of reaction

19. Inhibitors and activators
Inhibitor - substance that binds to an enzyme and decreases its activity
competitive inhibitors –compete with the substrate for the same active site
noncompetitive inhibitors –
bind to the enzyme in a location other than the active site
allosteric sites - specific binding sites acting as on/off switches

20. Factors Affecting Enzyme Activity
activator - substances that bind to allosteric sites and keep the enzymes in their active configurations.
*They can increase enzyme activity
cofactors - chemical components that facilitate enzyme activity
coenzyme *

21. Competitive inhibition Noncompetitive inhibition
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Substrate
Competitive
inhibitor
interferes
with active
site of
enzyme so
substrate
cannot bind
Substrate
Enzyme
Enzyme
Allosteric inhibitor
changes shape of
enzyme so it cannot
bind to substrate
Competitive inhibition
Noncompetitive inhibition

22. Regulation of Biochemical Pathways
Biochemical pathways must be coordinated and regulated to operate efficiently.
advantageous for cell to temporarily shut down biochemical pathways when their products are not needed
feedback inhibition
When the cell produces increasing quantities of a particular product, it automatically inhibits its ability to produce more

23. No end-product inhibition
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Initial
substrate
Enzyme 1
Intermediate A
Enzyme 2
Intermediate B
Enzyme 3
End product
No end-product inhibition