enzymes
TRANSCRIPT
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Biochemistry for nurses
ENZYMES
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Biochemistry for nurses
Enzymes are biocatalysts that speed up biochemical reactions (mostly
involved in the digestion and metabolism reactions)
Enzymes are not destroyed in their reactions; they are used over and
over again
Chemicals reacting with enzymes are called Substrates Substrate (S) binds to enzyme (E) during its reaction to form a product (P):
E + S ES P + ESimplest case!
Enzymes definition
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Biochemistry for nurses
Enzymes definition
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Biochemistry for nurses
Enzymes catalyze biological reactions
Enzymes have very strong catalytic power; rate of reactions can be
million or billion times faster than those in absence of enzymes
Ex: Oxidation (burning) of Glucose, by Glucose Oxidase (enzyme),
catalyzes glucose to react with oxygen (O2) with a very high-energy
release. However, exposing a container of glucose to the air (O2) for
years will cause no detectable reaction.
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Glucose oxidase is widely used for the determination of free glucose in sera or blood
plasma for diagnostics, using spectrometric assays.
Example:
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Biochemistry for nurses
Enzymes catalyze biological reactions
Enzyme catalysts reduce the activation
energy required, thereby increasing the
rate of reaction.
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The reaction goes very fast in the presence of Enzymes!
More examples:Enzyme Substrate Product Rate without
enzyme (umoles/liter per
min)
Rate with enzyme
(umoles/liter per min)
Acceleration due to Enzyme
Hexokinase Glucose Glucose 6-P < 0.0000001 1300 X 13 billion
Alcohol dehydrogenase
Ethanol Acetaldehyde < 0.000006 2700 X 450 million
Creatine-Kinase
Creatine Creatine phosphate
< 0.003 40 X 13,000
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Substrates Bind to the Active Sites of Enzymes
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Substrates Bind to the Active Sites of Enzymes
Example: DNA polymerase
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Example:
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Classification
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The Maximun Rate of an Enzymatic Reaction is Proportional to the Substrate Concentration!
AB
C
X
Saturation point
-----------------------Rmax (Maximun rate)
[Enzyme] = Constant
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Effect of Enzyme Concentration on the Reaction Rate
In case of a substrate concentration unlimited, an increase of the enzyme concentration causes an increase of the reaction rate!
More enzymes can react with more substrate molecules
[S]= ∞
[E] Rate
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Effect of Enzyme Concentration on the Reaction Rate
[E1] > [E2]
[E1] < [E2] ???
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Effect of Enzyme Concentration on the Reaction Rate
[E1] > [E2]
[E1] < [E2]
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Enzymes are Very Sensitive to Change in pH
Enzyme have a pH optimum, i.e. they have optimal activity at certain pH
Most enzyme exhibit optimal activity at pH value between 5 and 9 If the pH is too low (high H+ concentration) or too high (low H+
concentration) the enzyme activity will fall pH sensitivity is due to an ionization of the enzyme which results in
denaturation of enzyme (change in protein structure will cause
precipitation = loss of solubility of enzyme protein in water)
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Biochemistry for nurses
Enzymes are Very Sensitive to Change in pH
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Enzymes are Adapted to their pH Environment
Cells, blood and saliva have a pH close to 7
Stomach has a pH of 1-2 during digestion.
The graphe below shows the activities of 2 different enzymes, one
adapted to work in the stomach (Pepsin) and the other adapted to work
in the small intestine (Trypsin).
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Enzymes are Very Sensitive to Change in Temperature
Enzyme activity increases with
temperature up to about 45°C
With increasing temperature the
kinetic movement of enzyme and
substrate molecule increases, and
the chances of interaction between
enzyme and substrate molecule is
also increased, thereby
increasing the rate of reaction.
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Enzymes are Very Sensitive to Change in Temperature
Denaturation of enzyme by temperature is IRREVERSIBLE!!
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CoENZYMES and CoFactors
CoEnzymes and CoFactors are molecules which
are required for the enzyme activity.
CoEnzymes and CoFactors are not proteins! Many enzymes cannot function without them!!
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ApoEnzyme = Inactive Enzyme HoloEnzyme = Active Enzyme
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Examples of Vitamin and their coEnzymatic Function
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CoENZYMES and CoFactors function
ApoEnzymeHoloEnzyme
HoloEnzyme
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Conjugated Enzyme Structure
Some apoEnzymes need both a coEnzyme and a CoFactor
to become active!
HoloEnzymes
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Biochemistry for nurses
In living cells, all these reactions need Enzymes to function!!
Metabolism: The sum of chemicals reaction in a living cell
Catabolism: The process in which molecules are broken down to release
energy. Some of the energy released is captured for the synthesis of ATP
Anabolism: The process by which large molecules are synthesized using
smaller molecules that uses energy provided by ATP molecules.