Transcript Enzyme

Objective: You will be able to discuss how ATP is used
as the central molecule used in metabolism.
Do Now:
• Read all of page 49
• Look at the two reactions at the bottom of the
page
– For each reaction:
• List the reactant(s)
• List the product(s)
Organization of the Chemistry of Life into
Metabolic Pathways
• A metabolic pathway has many steps
– That begin with a specific molecule and end
with a product
– That are each controlled by a specific enzyme
Enzyme 1
A
Enzyme 3
D
C
B
Reaction 1
Starting
molecule
Enzyme 2
Reaction 2
Reaction 3
Product
Two Types of Metabolism
• Catabolic pathways
– Break down complex molecules into simpler
compounds
– Release energy
• Anabolic pathways
– Build complicated molecules from simpler ones
– Consume energy
The Structure and Hydrolysis of ATP
• ATP (adenosine triphosphate)
– Is the cell’s energy shuttle
– Provides energy for cellular functions
Adenine
N
O
O
-O
O
-
O
-
Phosphate groups
Figure 8.8
O
O
C
C
N
HC
O
O
O
NH2
N
CH2
-
O
H
N
H
H
H
OH
CH
C
OH
Ribose
• Energy is released from ATP
– When the terminal phosphate bond is broken
P
P
P
Adenosine triphosphate (ATP)
H2O
P
i
+
Figure 8.9 Inorganic phosphate
P
P
Adenosine diphosphate (ADP)
Energy
The Regeneration of ATP
ATP hydrolysis to
ADP + P i yields energy
ATP synthesis from
ADP + P i requires energy
ATP
Energy from catabolism
(exergonic, energy yielding
processes)
Energy for cellular work
(endergonic, energyconsuming processes)
ADP + P
Figure 8.12
i
Objective: You will be able to discuss how enzymes
speed up chemical reactions.
Do Now:
• Read all of page 50
• What is meant by activation energy?
Figure 2-19 Chemical Reactions
Section 2-4
Energy-Absorbing Reaction
Energy-Releasing Reaction
Activation
energy
Products
Activation energy
Reactants
Reactants
Products
Figure 2-19 Chemical Reactions
Section 2-4
Energy-Absorbing Reaction
Energy-Releasing Reaction
Activation
energy
Products
Activation energy
Reactants
Reactants
Products
Enzymes
• Are proteins so they are made of amino acids
• Work as catalysts to speed up reactions
• Usually end in –ASE
• Work on what is called a substrate
• Have a place called the active site that the
substrate goes into
• Are very specific
8.14
A
B
C
D
Free energy
Transition state
A
B
C
D
EA
Reactants
A
B
∆G < O
C
D
Products
Progress of the reaction
Speeding up chemical reactions
• Enzymes work by lowering the activation
energy (EA)
• The active site can lower an EA barrier by
– Orienting substrates correctly
– Straining substrate bonds
• The effect of enzymes on reaction rate
15
Course of
reaction
without
enzyme
EA
without
enzyme
EA with
enzyme
is lower
Free energy
Reactants
∆G is unaffected
by enzyme
Course of
reaction
with enzyme
Products
Progress of the reaction
igure 8.16
Substate
Active site
Enzyme
(a)
Enzyme- substrate
complex
Figure 8.16
(b)
Objective: You will be able to describe how enzymes
carry out a reaction.
Do Now:
• Read “Enzyme Action” on p. 52-53
• Why are enzymes compared to a lock and key?
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Figure 2-21 Enzyme Action
Section 2-4
Enzyme
(hexokinase)
Glucose
Substrates
Products
ADP
Glucose-6phosphate
Products
are released
ATP
Active site
Enzyme-substrate
complex
Substrates
are converted
into products
Substrates
bind to
enzyme
Figure 2-21 Enzyme Action
Section 2-4
Enzyme
(hexokinase)
Glucose
Substrates
Products
ADP
Glucose-6phosphate
Products
are released
ATP
Active site
Enzyme-substrate
complex
Substrates
are converted
into products
Substrates
bind to
enzyme
Figure 2-21 Enzyme Action
Section 2-4
Enzyme
(hexokinase)
Glucose
Substrates
Products
ADP
Glucose-6phosphate
Products
are released
ATP
Active site
Enzyme-substrate
complex
Substrates
are converted
into products
Substrates
bind to
enzyme
Figure 2-21 Enzyme Action
Section 2-4
Enzyme
(hexokinase)
Glucose
Substrates
Products
ADP
Glucose-6phosphate
Products
are released
ATP
Active site
Enzyme-substrate
complex
Substrates
are converted
into products
Substrates
bind to
enzyme
Induced fit
• Implies that enzymes are specific
• Only one substrate will fit into the active site of
an enzyme
• Once the substrate enters the active site, the
shape of the active site will change slightly
igure 8.16
Substate
Active site
Enzyme
(a)
Enzyme- substrate
complex
Figure 8.16
(b)
Objective: You will be able to discuss the impact that
temperature and pH will have on enzyme action.
Do Now:
• Read “Regulation of enzyme activity on ” on p. 53
• List all of the ways that enzyme activity can be
regulated
Effects of Temperature and pH
• Each enzyme
– Has an optimal temperature 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
Scientific Experiment Design
• Identify independent and dependent
variables
• Describe experimental treatment
• Identify the control setup
• State a hypothesis with reason
• Outline the experimental procedures
• Describe expected results
• Provide an explanation for results
Controlled Experiments
• Have an manipulated variable (Independent)
– The “thing” that you are changing
• Have a responding variable (Dependent)
– The “thing” that is affected when you change
the independent variable
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Example
• Which color light works best for
photosynthesis?
• What is the:
– Independent (manipulated) variable?
– Dependent (responding) variable?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Controlled experiments
• Also use one setup known as the control group
• A control group is where the manipulated
variable is removed
• You can think of the control group as being
used for comparison
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Examples of controls
• What color light is best for photosynthesis?
– Control is one that does not have a particular
color of light.
• Will plants grow more if fertilizer is added?
– Control is the setup that does not get the
fertilizer
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
You try
• What affect does the intensity of light have on
photosynthesis?
• Using a partner come up with the:
– Manipulated variable
– Responding variable
– Control group
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Problems
1. Will plants carry out more photosynthesis if
they are given more CO2?
2. Will plants grow more if they are exposed to
“dark light”?
3. Can plants produce more oxygen if you talk
to them?
4. What type of music will cause plants to
release more oxygen?
5. What effect does temperature have on the
growth of plants?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Enzyme Inhibitors
• Competitive inhibitors
– Bind to the active site of an enzyme, competing with
the substrate
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
(b) Competitive inhibition
Competitive
inhibitor
• Noncompetitive inhibitors
– Bind to another part of an enzyme, changing
the function
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
Feedback Inhibition
• 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)