Download Amino Acids, Proteins, and Enzymes

Amino Acids, Proteins, and Enzymes
Enzymes
Enzyme Action
Factors Affecting Enzyme Action
Enzyme Inhibition
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Enzymes
• Catalysts for biological reactions
– Catalyst: Substance that speeds up a chemical reaction
without being used in the process
• Most are proteins
• Lower the activation energy
– Minimum energy required to start a reaction
• Increase the rate of reaction
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Enzyme Action and the Hydrolysis of
Sucrose
Enzyme Sucrase
breaks down a
molecule of
sucrose into
glucose and
fructose
http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072965819&alaid=ala_1032271&showSelfStudyTree=true
What do enzyme names tell us?
• Enzyme names usually end in –ase
• Identifies a reacting substance
sucrase – breaks down sucrose
lipase - breaks down lipids
• Describes function of enzyme
oxidase – catalyzes oxidation
hydrolase – catalyzes hydrolysis
• Common names of digestion enzymes still use –in
ex. pepsin, trypsin
What do you think lactase does? …Manon???
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Important Enzyme Terms
Substrate: Reactant(s) an enzyme is acting on
ex. what is the substrate sucrase acts on?
Active Site: The location on the enzyme where the
substrate binds
Enzyme-Substrate Complex: An enzyme with its
substrate attached to the active site
2 Models for Enzyme Action
1. Lock and Key Model
2. Induced Fit Model
Enzyme Action:
Lock and Key Model
• An enzyme binds a substrate in a region called the active
site
• Only certain substrates can fit the active site
• Amino acid R groups in the active site help substrate bind
• Enzyme-substrate complex forms
• Substrate reacts to form product
• Product is released
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Lock and Key Model
Lock and Key Model
Lock and Key Model
P
+
S
+
S
P
E
+ S
ES complex
E + P
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Enzyme Action:
Induced Fit Model
• Enzyme structure flexible, not rigid
• Enzyme and active site adjust shape to bind
substrate
• Increases range of substrate specificity
• Shape changes also improve catalysis during
reaction
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Enzyme Action:
Induced Fit Model
P
S
S
P
E
+
S
ES complex
E
+
P
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Learning Check
A. The active site is
(1) the enzyme
(2) a section of the enzyme
(3) the substrate
B. In the induced fit model, the shape of the
enzyme when substrate binds
(1) Stays the same
(2) adapts to the shape of the substrate
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Solution E2
A. The active site is
(2) a section of the enzyme
B. In the induced fit model, the shape of the
enzyme when substrate binds
(2) adapts to the shape of the substrate
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Practice Questions
• Complete the 2 practice questions at the end
of the worksheet with a partner
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Factors Affecting Enzyme Action:
Temperature
• Little activity at low temperature
• Rate increases with temperature
• Most active at optimum temperatures (usually
37°C in humans)
• Activity lost with denaturation at high temperatures
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Factors Affecting Enzyme Action
Optimum temperature
Reaction
Rate
Low
High
Temperature
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Factors Affecting Enzyme Action:
Substrate Concentration
• Increasing substrate concentration increases the
rate of reaction (enzyme concentration is constant)
• Maximum activity reached when all of enzyme
combines with substrate
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Factors Affecting Enzyme Action
Maximum activity
Reaction
Rate
substrate concentration
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Factors Affecting Enzyme Action: pH
• Maximum activity at optimum pH
• The pH affects the R group of the amino acid
– Changing the pH changes the charge on R groups which
changes the tertiary structure of the enzyme
• Different enzymes have a different optimal pH
– Pepsin works best at a pH of 2 (found in the stomach)
– Trypsin works best at a pH of 8 (found in small intestine)
• Most lose activity in low or high pH
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Factors Affecting Enzyme Action
Reaction
Rate
Optimum pH
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5
7 9 11
pH
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Learning Check E3
Sucrase has an optimum temperature of 37°C and
an optimum pH of 6.2. Determine the effect of the
following on its rate of reaction
(1) no change (2) increase (3) decrease
A. Increasing the concentration of sucrose
B. Changing the pH to 4
C. Running the reaction at 70°C
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Solution E3
Sucrase has an optimum temperature of 37°C and
an optimum pH of 6.2. Determine the effect of the
following on its rate of reaction
(1) no change (2) increase (3) decrease
A. 2, 1 Increasing the concentration of sucrose
B. 3 Changing the pH to 4
C. 3 Running the reaction at 70°C
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Potato Lab
• How do these factors relate to the lab we are
doing today?
• What is the enzyme in this lab?
• What is the substrate in this lab?
• Which factors affecting enzyme action are we
manipulating?
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Time to Plan!
• As a group you need to design the procedure
for the second half of the lab
• When your group has agreed on the
procedure share it with me for approval
• Once it is approved everyone needs to write
the procedure into their lab handout
• All written procedures, observations, and
questions need to be completed in your own
words
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Safety Precautions
• What safety precautions do you think are
necessary for this lab?
• Materials:
– 3% Hydrogen Peroxide (purchased at the drug
store, used as a disinfectant for cuts)
– Potato blended with water
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Enzyme Inhibition
Inhibitors
• cause a loss of catalytic activity
• Change the protein structure of an enzyme
• May be competitive or noncompetitive
• Some effects are irreversible
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Competitive Inhibition
A competitive inhibitor
• Has a structure similar to substrate
• Occupies active site
• Competes with substrate for active
site
• Has effect reversed by increasing
substrate concentration
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Noncompetitive Inhibition
A noncompetitive inhibitor
• Does not have a structure like substrate
• Binds to the enzyme but not active site
• Changes the shape of enzyme and active site
• Substrate cannot fit altered active site
• No reaction occurs
• Effect is not reversed by adding substrate
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Learning Check E4
Identify each statement as describing an inhibitor
that is
(1) Competitive (2) Noncompetitive
A. Increasing substrate reverses inhibition
B. Binds to enzyme, not active site
C. Structure is similar to substrate
D. Inhibition is not reversed with substrate
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Solution E4
Identify each statement as describing an inhibitor
that is
(1) Competitive (2) Noncompetitive
A.
B.
C.
D.
1
2
1
2
Increasing substrate reverses inhibition
Binds to enzyme, not active site
Structure is similar to substrate
Inhibition is not reversed with substrate
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Allosteric Regulation
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Allosteric Regulation
Allosteric Regulation: A method used by cells to control enzyme activity
Allosteric Sites:
• A receptor site that is located some distance from the active site
• Binds substances that inhibit or stimulate an enzyme’s activity
Activator: Binding to allosteric site on enzyme stabilizing the protein
conformation keeping the active site available for the substrate
Allosteric Inhibitor: Binding to allosteric site on enzyme stabilizing the
protein conformation keeping the active site UNavailable for the
substrate
…Does this sound familiar???
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Applications of Enzymes
• Used in laundry detergents!
– Combincation of Proteases, Lipases, and Amylases
• Lactase for lactose intolerant people!
– Can be eaten in a pill
– Milk/dairy products can be pre-treated
• Meat Tenderizer
– Protease can be added to tough cuts of meat to make
the meat more tender
• Contact Lens Solution
– Proteases and lipases added to get rid of dirt
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Homework:
Use of Enzymes- Reading
• Answer the questions on the question sheet
using the information in the reading
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Homework:
Complete your portfolio for Unit 1
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Unit Test: Biochemistry
• There are review questions on the website
• I will also post the review questions created by
your peers
• Will be next Saturday at the start of class
• Will cover all the material we have discussed
in the biochemistry unit (including questions
from your lab!)
• If you are unclear about any of these concepts
please email me!
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