3/3 Daily Catalyst Pg. 87 Enzymes
 1. Mrs. Ireland has an elastic band wrapped around her finger
ready to attack the next student that does not do their AP
Biology homework. What type of energy does this elastic band
represent?
 2. What type of energy does ATP posses?
 3. In a population of 500, 142 people have the trait for a disease
known as the AP Biology homework slacker disease (A). What is
the frequency of q allele and the hybrid trait?
3/3 Class Business
 Quiz #22 Enzymes on Wednesday
 Lab on Wednesday
 Test grade
 Unit Test #8 Energy on Friday




Review day on Thursday
Extra credit article due Tuesday (3/10)
Test corrections due Tuesday (3/10)
Tutoring after school, during fourth, and during lunch
 Schedule with Mrs. Ireland
3/3 Agenda Pg. 87 Enzymes
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
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Daily Catalyst
Class Business
Finish reviewing quiz #21
Intro to enzymes
Exit ticket
Key Concepts
 An organism’s metabolism transforms matter and energy,
subject to the laws of thermodynamics
 The free-energy change of a reaction tells us whether the
reaction occurs spontaneously
Question #
Reviewer
1
Daquine
2
Kordell
3
Travia
4
Daquine
5
Yennifer
6
Teresa
7
Tiana
8
Bristin
9
Kiandria
10
Taylor
11
Anthony
12
Quinshelle
13
Tiffany
14
Daniel
15
John
16
Annie
Concept 8.4: Enzymes speed up metabolic
reactions by lowering energy barriers
 Key Point #1: A catalyst Is a chemical agent that speeds up a reaction without being
consumed by the reaction
 Key Point #2: Enzymes A protein catalyst
 “ase”
 How do enzymes speed up a reaction?
They Lower the activation barrier
The Activation Barrier
 Energy is needed to break and make bonds. This is what we
call a reaction.
 Key Point #3: The activation energy, EA
 Is the initial amount of energy needed to start a reaction
 Heat or energy
 The energy profile for an exergonic reaction
A
B
C
D
Free energy
Transition state
A
B
C
D
EA
Reactants
A
B
C
D
∆G < O
Products
Progress of the reaction
 I mentioned heat before as the energy source. Why is heat not
always the best option in a cell?
 Key Point #4: Enzymes speed up reactions by lowering the
activation energy.
 Same product is made
 Still exergonic or endergonic
 JUST FASTER!
 The effect of enzymes on reaction rate
Course of
reaction
without
enzyme
EA
without
enzyme
Free energy
EA with
enzyme
is lower
Reactants
∆G is unaffected
by enzyme
Course of
reaction
with enzyme
Products
Progress of the reaction
Figure 8.15
Substrate Specificity of Enzymes
 For enzymes to speed up a reaction, they need to bind to the
substrate (reactant)
 Key Point #5: Enzyme binds to the substrate
 Forms the enzyme-substrate complex (ES complex)
Can the substrate bind anywhere?
 Key Point #6: The active site
 Is the region on the enzyme where the substrate binds
 Lock and key
Substate
Active site
Enzyme
Figure 8.16
(a)
 Key Point #7 Induced fit of a substrate:
 Once bound, the active site changes shape so that the
substrate fits even better.
Enzyme- substrate
complex
Figure 8.16
(b)
Reusable
 Key Point #8: Enzymes are not consumed in the reaction.
They are reusable for the next reaction!
 The catalytic cycle of an enzyme
1 Substrates enter active site; enzyme
changes shape so its active site
embraces the substrates (induced fit).
Substrates
Enzyme-substrate
complex
6 Active site
Is available for
two new substrate
Mole.
Enzyme
5 Products are
Released.
Figure 8.17
Products
2 Substrates held in
active site by weak
interactions, such as
hydrogen bonds and
ionic bonds.
3 Active site (and R groups of
its amino acids) can lower EA
and speed up a reaction by
• acting as a template for
substrate orientation,
• stressing the substrates
and stabilizing the
transition state,
• providing a favorable
microenvironment,
• participating directly in the
catalytic reaction.
4 Substrates are
Converted into
Products.
 Key Point #9: The active site can lower an EA barrier by:




Orienting substrates correctly
Straining substrate bonds
Providing a favorable microenvironment
Covalently bonding to the substrate
 Key Point #10: Transition state: The reactive (unstable) condition of the substrate
 Enzymes help the substrate reach the transition state by
straining substrate bonds so they break easily.
Enzyme activity
 Key Point #11: Enzyme activity also relies on the substrate
concentration.
 Increase [substrate] = increase E-S complexes
 Eventually the solution will be saturated with substrates and more
enzymes will be needed.
Effects of Local Conditions on
Enzyme Activity
 The activity of an enzyme
 Is affected by general environmental factors
Effects of Temperature and pH
 Key Point #12: Each enzyme has 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
 Has an optimal pH in which it can function
Optimal pH for pepsin
(stomach enzyme)
Rate of reaction
Optimal pH
for trypsin
(intestinal
enzyme)
3
4
0
2
1
(b) Optimal pH for two enzymes
Figure 8.18
5
6
7
8
9
Example
Cofactors
 Key Point #13: Enzyme assistance Cofactors
 Are nonprotein enzyme helpers
 Coenzymes
 Vitamins
¾ Daily Catalyst Pg. 88 Control of enzymes
 1. A very large population of randomly-mating laboratory mice
contains 35% white mice. White coloring is caused by the double
recessive genotype, "aa". Calculate allelic and genotypic
frequencies for this population.
 2. Describe the induced fit model of enzymes.
 3. Use the word optimal in a sentence.
 4. Label the following diagram:
¾ Daily Catalyst Pg. 88 Control of
enzymes
 1.
 A very large population of randomly-mating laboratory mice contains
35% white mice. White coloring is caused by the double recessive
genotype, "aa". Calculate allelic and genotypic frequencies for this
population. Answer: 35% are white mice, which = 0.35 and represents
the frequency of the aa genotype (or q2). The square root of 0.35 is
0.59, which equals q. Since p = 1 - q then 1 - 0.59 = 0.41. Now that we
know the frequency of each allele, we can calculate the frequency of
the remaining genotypes in the population (AA and Aa individuals).
AA = p2 = 0.41 x 0.41 = 0.17; Aa = 2pq = 2 (0.59) (0.41) = 0.48; and as
before aa = q2 = 0.59 x 0.59 = 0.35. If you add up all these genotype
frequencies, they should equal 1.
¾ Daily Catalyst Pg. 88 Control of enzymes
 2. Describe the induced fit model of enzymes.
 Once the substrate binds to the enzyme at the active site, the active
site morphs to better form around the substrate to form a tighter
bond.
 3. Use the word optimal in a sentence.
 The optimal environment for taking the ACT on the 17th of March is a
silent location with a calculator that works.





4. Label the following diagram:
A-substrate
B-Active Site
C-Enzyme
D- Product
3/4 Class Business
 Quiz #22 Enzymes TODAY
 Lab on Wednesday
 Test grade
 Unit Test #8 Energy on Friday




Review day on Thursday
Extra credit article due Tuesday (3/10)
Test corrections due Tuesday (3/10)
Tutoring after school, during fourth, and during lunch
 Schedule with Mrs. Ireland
3/4 Agenda Pg. 88 Control of
Enzymes





Daily Catalyst
Class Business
Finish reviewing quiz #21
Intro to enzymes
Exit ticket
Cofactors- page 87
 Key Point #13: Enzyme assistance Cofactors
 Are nonprotein enzyme helpers
 Coenzymes
 Vitamins
Pg. 88 Control of Enzymes
 Concept 8.5: Regulation of enzyme activity helps control
metabolism
 A cell’s metabolic pathways must be tightly regulated
Enzyme Inhibitors
 Key Point #1: Competitive inhibitors
 Bind to the active site of an enzyme, competing with the
substrate
 The substrate cannot bind
A substrate can
bind normally to the
active site of an
enzyme.
Substrate
Active site
Enzyme
(a) Normal binding
A competitive
inhibitor mimics the
substrate, competing
for the active site.
Figure 8.19
Competitive
inhibitor
(b) Competitive inhibition
Enzyme Inhibitors
 Key Point #2: Noncompetitive inhibitors
 Bind to another part of an enzyme, changing the shape of the
active site
 The substrate CANNOT bind
A noncompetitive
inhibitor binds to the
enzyme away from
the active site, altering
the conformation of
the enzyme so that its
active site no longer
functions.
Noncompetitive inhibitor
Figure 8.19
(c) Noncompetitive inhibition
Allosteric Regulation of Enzymes
 Key Point #3: Allosteric regulation
 Is the term used to describe any case in which a protein’s function
at one site is affected by binding of a regulatory molecule at
another site
 Regulatory molecules bind to specific sites (allosteric sites) and
change the shape of the proteinchanging the shape of the
active site
 Inhibit or stimulate the enzyme
Allosteric Activation and Inhibition
 Many enzymes are allosterically regulated
 Enzymes change shape when regulatory molecules
bind to specific sites, affecting function
Allosteric enyzme
with four subunits
Regulatory
site (one
of four)
Active site
(one of four)
Activator
Active form
Stabilized active form
Oscillation
Allosteric activater
stabilizes active form
NonInactive form Inhibitor
functional
active
site
Figure 8.20
Allosteric activater
stabilizes active from
Stabilized inactive
form
(a) Allosteric activators and inhibitors. In the cell, activators and inhibitors
dissociate when at low concentrations. The enzyme can then oscillate again.
 Key Point #4: Cooperativity
 Is a form of allosteric regulation that can amplify enzyme activity
Binding of one substrate molecule to
active site of one subunit locks
all subunits in active conformation.
Substrate
Inactive form
Figure 8.20
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 in the TOOLBOX!
 Key Point #5: Cooperativity example
 In hemoglobin (red blood cells), when the first oxygen
binds to hemoglobin, it stabilizes hemoglobin and
encourages other oxygen's to bind (4 O2’s)
Feedback Inhibition
 Key Point #6: In feedback inhibition
 The end product of a metabolic pathway shuts down the pathway
 Feedback inhibition
Active site
available
Initial substrate
(threonine)
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Isoleucine
used up by
cell
Intermediate A
Feedback
inhibition
Active site of
enzyme 1 no
longer binds
threonine;
pathway is
switched off
Enzyme 2
Intermediate B
Enzyme 3
Intermediate C
Isoleucine
binds to
allosteric
site
Enzyme 4
Intermediate D
Enzyme 5
Figure 8.21
End product
(isoleucine)
Enzyme Lab
 Directions: With your partner, read the pre-lab
reading and answer the pre-lab questions. Write 4
hypotheses based on the scenarios given to you.
 Check in with Mrs. Ireland before you move on!
 Noise: 2 (with partner)
 Time: until 12:50
 James, Joe, and Paul (quiz at 8:30)