Enzymes

1. Enzymes
Biological catalysts used to speed up chemical reactions
(process is called catalysis)
Section 1.7

2. Role of Proteins

3. • Ex. Lactose needs to be broken up to create glucose + galactose
ome Activation Energy (Ea)
needed to break the
ond (usually heat)
However Ea required
would kill your cells.

4. •Enzymes are protein catalysts that work on specific
substrates
•They speed up a reaction (without being consumed) by
lowering Ea

5. How do Enzymes Lower Ea?
1. Use amino acid R groups to weaken the
bonds in the substrate
2. Put the substrate(s) in the correct
orientation
3. Transfer electrons to or from the substrate
to destabilize it (oxidative enzymes)
4. Add or remove H+
from the substrate
(hydrolytic enzymes)

6. Enzyme/substrate
•An enzyme has a special active site that will only fit a specific
substrate (or reactant)
•The active site will change shape (called the induced fit
model) and the reaction can proceed
•1000’s of substrates/second

7. •This process is repeated, know as the catalytic cycle

8. •Some enzymes require additional
molecules or ions to catalyze a reaction:
•Organic molecules that help enzymes are
called coenzymes (coenzyme-A, NAD+
, FAD)
•Ions that help are called cofactors

10. Rate of enzyme activity
Enzyme action is modified by:
1. Heat (excessive kinetic energy can denature)
2. pH (alters ionization of peptides)

11. 3. Enzyme concentration

12. Regulating Enzymes
Competitive Inhibition:
A inhibitor competes for an enzyme’s active site and slows down its
action.

13. Non-competitive inhibition:
1. Allosteric Regulation (inhibition): A non-competitive
inhibitor binds to a regulatory site called the allosteric site
and changes the shape of the active site so it no longer
accepts substrates.

14. 2. Feedback Inhibition: A group of enzymes in sequence
change a substrate until enough of the finished product
reacts with a regulatory site on the original enzyme,
stopping the sequence.
*Feedback regulation
is an important
concept in biology

15. Allosteric Regulation (activation): molecules
called activators can also bind to the allosteric
site and increase the enzyme’s activity

16. HWK
Pg. 57, Q. 1-13