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Enzymes
Lecture #14
Ms. Day
Honors Biology
Chemical Reactions
• Every chemical reaction
– Involves both bond breaking and bond
forming
– Initial amount of energy to start reaction =
activation energy (EA)
REACTANTS
CH2OH
CH2OH
H
PRODUCTS
O
O
H
H
OH
O
CH2OH
H
H HO
+
CH2OH
H
OH
Sucrose
C12H22O11
OH H
Sucrase
O
H
H
OH H
H2O
HO
CH2OH
O
H
OH
HO
H
H HO
CH2OH
H
OH
Glucose
C6H12O6
OH H
Fructose
C6H12O6
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
–
http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_enzym
es_work.html
ENZYMES LOWERS THE AMOUNT OF
ACTIVATION ENERGY NEEDED 
INCREASES SPEED OF REACTION
Enzyme Vocabulary
• The substrate
– Is the reactant an enzyme acts on
• The enzyme
– binds to its substrate, forming an
enzyme-substrate complex
http://1ps.googleusercontent.com/h/www.greydefence.com/wordpress/w
p-
• The active site
–Is the region on the enzyme
where the substrate binds
Substrate
C
Active site
B
Enzyme
(a)
D
E
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
• R
groups =
red
• POLAR w/
Charges
(+ or -)
HYDROPHILIC
• POLAR with
NO Charges
HYDROPHILIC
• Non polar
HYDROPHOBIC
Enzyme is
RECYCLED!!
Never used
up or
destroyed
EFFECTS OF TEMPERATURE & pH
• Enzymes have an optimal temperature
and pH in which it can function
Optimal temperature for
typical human enzyme
Optimal temperature for
enzyme of thermophilic
Rate of reaction
(heat-tolerant)
bacteria
0
20
40
Temperature (Cº)
(a) Optimal temperature for two enzymes
Figure 8.18
80
100
– Enzymes have an optimal pH in
which it can function
Optimal pH for pepsin
(stomach enzyme)
Rate of reaction
Optimal pH
for trypsin
(intestinal
enzyme)
0
1
2
3
(b) Optimal pH for two enzymes
4
5
6
7
8
9
What can destroy enzymes?
Denaturation = take away (or
lower) the function of protein
• pH
• Salt concentration
• Temperature
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+
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+
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
Enzyme
Inhibitors
Ex:
Poison/toxins or
drugs
[Enzymes]
• http://www.sumanasinc.com/webcontent/a
nimations/content/proteinstructure.html
• Denaturation and eggs
Let’s Practice…
Substrate (reactant)
Active site
Enzyme
Products
Let’s Practice…True/False
True
• _______
Enzymes interact with specific
substrates
True
• _______
Enzymes speed up reactions
False
• _______
Boiling temperature will increase the
rate of reaction
False
• ______
Enzymes increase activation energy
False
• _______
Changing the pH will not change the
rate of reaction
• _______
Freezing an enzyme will decrease the
True
rate of reaction