Enzymes in detail can be taught a part of it
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Transcript of Enzymes in detail can be taught a part of it
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Enzymes
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Enzymes
Enzyme- highly specific protein catalysts
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Enzyme Specificity
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Enzyme Specificity
• Lock and Key model
• Induced fit model– “polyaffinity mechanism”- three point attachment
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Catalyst
Catalyst- speeds up reaction without being consumed (no effect on equilibrium)
do so by lowering the activation energy of the rxn
activation energy- the amount of energy required to reach the transition state
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Catalyst
Catalyst- speeds up reaction without being consumed
do so by lowering the activation energy of the rxn
activation energy- the amount of energy required to reach the transition state
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Classes of Enzymes
Enzyme Commission (E.C.) 4.1.1.32
1. Oxidoreductases
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Coenzymes
Coenzyme- organic molecule required by an enzyme to catalyze rxn
Most coenzymes are vitamin derivatives (water sol)
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Classes of Enzymes
Enzyme Commission (E.C.) 4.1.1.32
1. Oxidoreductases- lactate dehydrogenase
2. Transferases- glucokinase
3. Hydrolases- chymotrypsin, G6Pase
4. Lyases- fumarase
5. Isomerases- phosphoglucoisomerase
6. Ligases- Acyl CoA synthetase
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Classes of Enzymes
1. Oxidoreductases
2. Transferases
3. Hydrolases
4. Lyases
5. Isomerases
6. Ligases
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Cofactors and Coenzymes
Cofactor- depends on context– either inorganic atom– or inorganic molecule or coenzyme
Coenzyme- organic molecule required by an enzyme for it’s catalytic activity, usually vitamin or vitamin derivative
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Coenzymes
1. Oxidoreductases
NAD+/NADH + H+
NADP+/NADPH + H+
FAD/FADH2
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NAD+/NADH
Niacin derivative
recognize structure
used for degradation
diffuses in and out of active site
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NADP+/NADPH
Almost identical to NAD+
used for synthesis
diffuses in and out of active site
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FAD/FADH2
Riboflavin derivative
used for degradation
Prosthetic group
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Coenzymes (table of vitamin, coenz form and function)
2. Transferases
TPP
THF
PLP
lipoic acid
vitamin B12
CoASH
6. Ligases
biotin
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Kinetics: Rate of Reaction
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Kinetics: Rate of Reaction
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Kinetics: Rate of Reaction
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Kinetics: Rate of Reaction
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Michaelis-Menton Kinetics
Eqn.
Vo
Vmax
Km
[S]
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Lineweaver-Burk Transformation
Eqn of transformation
slope and intercepts
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Michaelis-Menton Kinetics Substrate Concentration
[substrate]
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
velo
city
0.0
0.5
1.0
1.5
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Michaelis-Menton Kinetics Enzyme concentration
mL enzyme
0.0 0.3 0.6 0.9 1.2 1.5 1.8
velo
city
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
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Michaelis-Menton KineticsTemperature
temperature, oC
0 10 20 30 40 50 60 70
velo
city
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
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Michaelis-Menton KineticspH
pH
0 2 4 6 8 10 12
velo
city
0
5
10
15
20
25
30
35
40PepsinG6Pase
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Michaelis-Menton Kinetics Inhibitors or activators
• Activators- not discussed at this time
• Inhibitors- 3 types
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Enzyme Inhibition
Competitive inhibition-
Noncompetitive inhibition-
Uncompetitive inhibition-
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Example Problem [S],µmol vo, µmol/min
0.1 0.27
2.0 5
10.0 20
20.0 40
40.0 64
60.0 80
100.0 100
200.0 120
1000.0 150
2000.0 155
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Michaelis-Menton Plot
Substrate, µmol
0 500 1000 1500 2000
Vo,
µm
ol/m
in
0
20
40
60
80
100
120
140
160
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Example Problem
[S],µmol 1/[S], µmol-1 vo, µmol/min 1/vo, min/µmol
0.1 10 0.27 3.70
2.0 0.5 5 0.2
10.0 0.1 20 0.05
20.0 0.05 40 0.025
40.0 0.025 64 0.0156
60.0 0.0167 80 0.0125
100.0 0.01 100 0.01
200.0 0.005 120 0.0083
1000.0 0.001 150 0.0067
2000.0 0.0005 155 0.0065
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Lineweaver-Burk Plot
1/Substrate, 1/µmol
0.0 0.0 0.2 0.3 0.4 0.5
1/V
o, m
in/µ
mol
0.00
0.05
0.10
0.15
0.20
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Type of Inhibition
1/[S], mM-1
-1 0 1
v o,
µm
ol/m
L•s
ec
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
-I +I
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Enzyme Active Sites
Active site- that region of the enzyme where substrate binds and is converted to product
why the enzyme has to be bigger than substrate
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Ways in Which an Enzyme Performs Catalysis
Increase the effective concentration
Stabilize transition state
Put a strain on susceptible bonds
Hold reactants near each other and in the proper orientation
Form covalent bonds with substrate that result in destabilization of substrate
Act as proton donors and acceptors
Nucleophilic/Electrophilic attacks
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Amino Acids of the Active Siteget good example of each
X-ray crystallography
mutagenesis
amino acid modifying reagents
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Enzyme Regulation
On vs. off
1. Isoenzymes2. Covalent Modification3. Allosterism4. Repression5. Proenzymes
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Isoenzymes
LDH example
muscle vs. heart
tetramer
preferential substrate affinity
why?
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Covalent Modification
Phosphorylation most common
Others: sulfation, acetylation, methylation
glycogen phosphorylase vs. glycogen synthase
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Allosteric Activation/Inhibition
“Other site”
Sigmoidal kinetics
homo- vs. heterotropic
feedback inhibition vs. feedforward stimulation
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Repression
molecular biology section
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Proenzymes
AKA zymogens
alters the concentration of active enzyme
particularly common with:digestive enzymespeptide hormonesclotting factors
proteolysis is selective
dibasic example
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Proinsulin
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Other Cleavages