The activation energy
is the difference
between the energy
of the reactants and
the tip of the “hump”
on the diagram above.
RATE = change in a measurable quantity
Change in time
How Enzymes Work
Would this
reaction be
endergonic or
exergonic?
Macromolecules & the Enzymes that
Catalyze the Reactions
Polymerase
—catalyzes
polymer
formation
using
dehydration
synthesis
Hydrolase—
catalyzes the
breakdown of
polymers
using
hydrolysis
reactions
Why do
we store
hydrogen
peroxide
in a brown
bottle?
Remember enzymes
are proteins
with primary,
secondary,
tertiary and
quaternary structure.
Proteins usually end in the
suffix –in (insulin, actin). If the
protein is an enzyme, it often
ends in –ase (lactase, catalase)
Can’t fit!
“conformation” = shape!
The shape of the enzyme and more
specifically, it’s active site determines its
function.
All these H+ ions
made an acidic
environment that
denatured the protein
we call an enzyme.
The active site is
rendered useless.
When you see a
“bell curve”
or normal
distribution,
you’re dealing
With an optimum.
Drop a perpendicular
Line down from the peak of the
“bell” and
Read the x-axis to determine
The optimum.
BOTH temperature
AND pH exhibit
This type of a result in most
Biological settings.
It’s the 3 Bears scenario:
Too much,
Too little, and
JUST RIGHT!
Feedback Inhibition:The product forms
shuts down the process by binding the
enzyme at an allosteric site!
Yeah, I
hate them,
too!
This is a REDOX titration.
“OILRIG”
“Oxidation is loss” of electrons
“Reduction is gain” of electrons.
These two processes are always happening together.
We call them a set of “coupled” reactions.
YOU HAVEN’T HEARD THE LAST OF REDOX!
If you get the
“purple stuff”
on your skin,
It will stain!
H2O2 reduces
KMnO4 on your skin
to the colorless form
And thus, removes the
Stain!
Use it on the buret
As well.
Fancy word for
portion.
Allows for RELATIVE data. This reduces error. It’s not important that you get the same color
as your neighbor—it’s important you agree with YOURSELF on each titration.
Much easier to read
If your buret has
WHITE marks!
I call this an
easy
question.
You’ll call it
a TRICK
question!
Multiple Choice Question:
E1
E2
E3
W
X
Y
Z
1. In the series of enzyme reactions shown above, product Z
is able to occupy the active site of enzyme E2. Product Z
can therefore first inhibit the production of
(A) W
(B) E1
(C) X
(D) E2
(E) Y
Multiple Choice Question:
2. A substrate molecule may be bound to the
active site of an enzyme by all of the
following EXCEPT
(A) hydrogen bonds
(B) peptide bonds
(C) ionic bonds
(D) van der Waals interactions
(E) hydrophobic interactions
For the next 3 questions:
Multiple Choice Question:
3. In an experiment to test the effect of
amylase on starch, the control would be
(A) flask A only
(B) flask B only
(C) flask C only
(D) flasks A and B
(E) flasks A and C
Multiple Choice Question:
4. After 2 minutes, a positive test for sugar
would most likely be observed in
(A) flask A only
(B) flask B only
(C) flask C only
(D) flask A and C
(E) flask B and C
Multiple Choice Question:
5. Support for the hypothesis of enzyme denaturation
can be obtained by comparing starch digestion in
(A) flasks A and B after 5 minutes
(B) flasks B and C after 5 minutes
(C) flasks A and C after 5 minutes
(D) flask A at time zero and again after 5 minutes
(E) flask B at time zero and again after 5 minutes
Multiple Choice Question:
Questions 6 - 8
In a laboratory experiment using spectrophotometry, an enzyme is combined with its
substrate at time zero. The absorbance of the resulting solution is measured at time
zero and at five-minute intervals. In this procedure an increase in absorbance is related
to the amount of product formed during the reaction. The experiment is conducted
using the three preparations shown in the table below.
Absorbance
Enzyme Preparation
0 min
5 min 10 min 15 min 20 min
I. 3 mL of enzyme preparation
0.0
.22
.33
.38
.37
3 mL of substrate
pH 5.0
II. 3 mL of boiled enzyme preparation 0.0
.06
.04
.03
.04
2 mL of substrate
pH 5.0
III.3 mL of enzyme preparation
0.0
.32
.37
.36
.38
2 mL of substrate
pH 6.0
Multiple Choice Question:
6. The most likely reason for the failure of the absorbance to
increase significantly after 10 minutes in preparation III is
that
(A) the reaction is thermodynamically impossible at pH 6.0
(B) the enzyme is not active at this pH
(C) a pH of 6.0 prevents color development beyond an
absorbance of .38
(D) the enzyme is degraded more rapidly at pH 6.0 than it is
at pH 5.0
(E) most of the substrate was digested during the first 10
minutes
Multiple Choice Question:
7. Which of the following statements is best supported by the
data?
(A) Increasing the pH to 7.0 would yield an absorbance
higher than 0.30 after
5 minutes.
(B) The enzyme demonstrates more activity at pH 6.0 than at
pH 5.0.
(C) The enzyme has no activity at pH 6.0.
(D) A pH of 5.0 is the optimum for the activity of the
enzyme.
(E) The enzymatic activity is independent of pH.
Multiple Choice Question:
8. Which of the following can best be concluded from a
comparison of the results of preparation II with those of
preparation I?
(A) Heating the enzyme is not required to increase the
absorbance.
(B) Boiling does not break down the substrate.
(C) Most of the increase in the amount of product in
preparation I was due to an enzymatic degradation of the
substrate.
(D) Enzymatic reactions proceed at a faster rate after boiling
the enzyme.
(E) Products resulting from the breakdown of the enzyme are
responsible for the absorbance increase in preparation II.
Multiple Choice Question:
9. Which of the following can be used to
determine the rate of enzyme-catalyzed
reactions?
(A) Rate of disappearance of the enzyme
(B) Rate of disappearance of the substrate
(C) Rate of disappearance of the product
(D) Change in volume of the solution
(E) Increase of activation energy
Multiple Choice Question:
10. Within the cell, many chemical reactions that, by
themselves, require energy input (have a positive freeenergy change) can occur because the reactions
(A) may be coupled to the hydrolysis of ATP
(B) take place very slowly
(C) take place when the cells are at unusually high
temperatures
(D) are catalyzed by enzymes
(E) are aided by various metal ions that act as catalysts
For the next 4 questions: Refer to the following
graph. The solid curve and the dashed curve
represent alternate pathways for the same
reaction. One pathway is enzyme catalyzed.
Multiple Choice Question:
11. Represent the activation energy of the enzymecatalyzed reaction
Multiple Choice Question:
12. Represents the net energy change of the reaction
Multiple Choice Question:
13. Represent the energy state of the products of the
enzyme-catalyzed pathway
Multiple Choice Question:
14. Represents the energy state of the products of the
pathway that is not enzyme-catalyzed
FR Questions…
1994: Enzymes are biological catalysts.
a. Relate the chemical structure of an enzyme
to its specificity and catalytic activity.
FR Questions…
1994:
a.
4 points maximum
Enzymes are biological catalysts.
Relate the chemical structure of an enzyme to its specificity and catalytic activity.
•Protein with details of structure
•Primary, secondary, tertiary, quaternary structure explained and related to 3-D
shape
•Bonding [α- helix, β-pleated sheet, H-bonding, S-S bridges, hydrophobic
interactions
•Active site—lock and key—substrate
•Activators, inhibitors
•Induced fit theory
•Activation energy lowered
•Substrate altered
FR Questions…
1994: Enzymes are biological catalysts.
b. Design a quantitative experiment to
investigate the influence of pH or
temperature on the activity of an enzyme.
FR Questions…
5 points maximum
1994: Enzymes are biological catalysts.
b. Design a quantitative experiment to investigate the influence of pH or temperature on the
activity of an enzyme.
•Eliminate, control other variables
•Negative control [setup without enzyme OR enzyme without substrate]
•Describe experimental variable [temp or pH] VALUES or RANGES
•Use correct enzyme—substrate pair!
•Measure disappearance of substrate or appearance of product, heat production, etc.
•Report data, predicted results, such as loss of activity, reduced activity, or no change in
activity
•Elaboration of experiment—rate calculation explained, identify independent and
dependent variables, repeat for reliability, etc.
FR Questions…
1994: Enzymes are biological catalysts.
c. Describe what information concerning the
structure of an enzyme could be inferred
from your experiment.
FR Questions…
2 points maximum
1994: Enzymes are biological catalysts.
c. Describe what information concerning the structure of an enzyme
could be inferred from your experiment.
•Correct link of predicted results to changes in enzyme structure
•Range of activity implies slight change in enzyme STRUCTURE
•Loss of activity implies denaturation [must explain denaturation]
•No loss in activity implies no change in structure
•Elaboration on changes in enzyme structure
•Conformation explanation, bonding shifts
•Explanation of why no change in activity is predicted
FR Questions…
1988: After an enzyme is mixed with its substrate, the amount
of product formed is determined at 10-second intervals for 1
minute. Data from this experiment are shown below:
Time (s)
Product
Formed (mg)
0
10
0.0 0.25
20
30
40
50
60
0.50
0.70
0.80
0.85
0.85
Draw a graph of these data and answer the following
questions.
Graph of the data:
Of
course,
your
graph
would be
hand
sketched!
3 points!
•Time on x
(independent)
& product
on y-axis
(dependent)
•Scale and
Label axes
•Plot points—
Curve MUST
Be drawn
To earn this
Point!
RATE = change in a measurable quantity = (0.25-0.0 mg) = 0.025 mg/s INITIAL RATE
Change in time
(10-0 sec)
3 points!
FR Questions…
a. What is the initial rate of this enzymatic
reaction?
INITIAL RATE = change in a measurable quantity = (0.25-0.0 mg) = 0.025 mg/s
Change in time
(10-0 sec)
b. What is the rate after 50 seconds?
Why is it different from the initial rate?
RATE after 50 sec = change in a measurable quantity = (0.85-0.85 mg) = 0.0 mg/s
Change in time
(60-50 sec)
since EQUILIBRIUM has been achieved [the graph flattens out or levels off!]
•Setup for
Rate calculation
•Units correct
•Why?
Equilibrium
Has been
reached!
FR Questions…
c. What would be the effect on product
formation if the enzyme were heated to a
temperature of 100 oC for 10 minutes before
repeating the experiment? Why?
Stops reaction; no product formation;
rate near or at zero
1 pt
Conformational shape change - denaturation
1 pt
FR Questions…
d. How might altering the substrate
concentration affect the rate of the reaction?
Why?
Change: (1 pt)
•Increase amt. of substrate—no change in rate, initial slope the same!
May take longer to level off.
•Decrease amt. of substrate— decrease the slope, decrease the rate—takes
less time to level off.
Explanation: (1pt)
•Increase—Enzyme becomes saturated and is working as fast as it can!
•Decrease—Enzyme is no longer saturated or at least further from saturation
FR Questions…
e. How might altering the pH affect the rate of
reaction? Why?
Change:(1pt)
Slight change may affect the curve either way
Drastic change may stop the reaction
Explanation:(1pt)
Enzyme has an optimum pH
Enzyme can be denatured by extremes