ert211 chp 1-2.pdf
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ERT 211/1
Biochemical Engineering
CHAPTER 1:THE KINETICS OF ENZYME
CATALYZED REACTIONS
BY:
EN. MOHD. FAHRURRAZI TOMPANG
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Classification of Enzyme
Enzymes fall into 6 classes based on function
1. Oxidoreductases: which are involved in oxidation,reduction, and electron or proton transfer reactions
2. Transferases : catalysing reactions in which groupsare transferred
3. Hydrolases : which cleave various covalent bonds byhydrolysis
4. Lyases : catalyse reactions forming or breakingdouble bonds
5. Isomerases : catalyse isomerisation reactions
6. Ligases : join substituents together covalently.
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Enzyme Reaction
For design and analysis of a reacting system, wemust have a mathematical formula which gives thereaction rate
in terms of composition,
temperature,
and pressure of the reaction mixture.
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Enzyme Kinetics
Enzymes are protein catalysts that, like all catalysts,speed up the rate of a chemical reaction withoutbeing used up in the process.
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Enzyme Kinetics
Synthetic catalysts and enzymes use the commontechnique for modeling reaction kinetics.
The rate expressions eventually obtained for both
types of catalysts are very similar and sometimes ofidentical forms.
This is because, in both cases, the reacting moleculesform some sort of complex with the catalyst.
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Enzyme Kinetics
Most synthetic catalysts are not specific; i.e. they willcatalyze similar reactions involving many differentkinds of reactants.
While some enzymes are not very specific, many willcatalyze only one reaction involving only certainsubstrates.
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Explain why enzyme catalysis are nonspecific butenzyme catalysis are specific?
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Define Cofactors
Apoenzyme
Holoenzyme
coenzyme
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Enzyme Kinetic
Enzyme is a catalyst which increases the rate of achemical reaction without undergoing a permanentchemical change.
While a catalyst influences the rate of a chemicalreaction, it does not affect reaction equilibrium.
Equilibrium concentrations can be calculated usingonly the thermodynamic properties of the substrates
and products.
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Enzyme
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Enzyme Kinetics
Both synthetic and biological catalysts can graduallylose activity as they participate in chemical reactions.
However, enzymes are in general far more fragile.
Enzymes contorted shapes in space often endowenzymes with unusual specificity and activity
It is relatively easy to disturb the nativeconformation and destroy the enzyme's catalytic
properties.
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Enzyme Kinetics
It is often asserted that enzymes are more active, i.e.,allow reactions to go faster, than nonbiological catalysts.
At the ambient temperatures where enzymes are mostactive they are able to catalyze reactions faster than themajority of artificial catalysts.
When the reaction temperature is increased, solid(synthetic) catalysts may become as active as enzymes.
The enzyme activity does not increase continuously asthe temperature is raised. Instead, the enzyme usuallyloses activity at quite a low temperature, often onlyslightly above that at which it is typically found.
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Enzyme reaction rates are determined by severalfactors.
Concentration of substrate molecules
The more of them available, the quicker the enzyme moleculescollide and bind with them).
The concentration of substrate is designated [S] and is expressed in
unit of molarity. Temperature.
As the temperature rises, molecular motion - and hence collisionsbetween enzyme and substrate - speed up.
But as enzymes are proteins, there is an upper limit beyond which
the enzyme becomes denatured and ineffective.
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Enzymes cont.
the presence of inhibitors. competitive inhibitors are molecules that bind
to the same site as the substrate - preventing thesubstrate from binding as they do so - but are not
changed by the enzyme. noncompetitive inhibitors are molecules that
bind to some other site on the enzyme reducing itscatalytic power.
pH. The conformation of a protein is influenced by pHand as enzyme activity is crucially dependent on itsconformation, its activity is likewise affected.
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How we determine how fast an enzymeworks
We set up a series of tubes containing gradedconcentrations of substrate, [S] . At time zero,we add a fixed amount of the enzymepreparation.
Over the next few minutes, we measure theconcentration of product formed. If theproduct absorbs light, we can easily do this ina spectrophotometer.
Early in the run, when the amount ofsubstrate is in substantial excess to theamount of enzyme, the rate we observe is theinitial velocity ofVi.
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THE ENZYME-SUBSTRATECOMPLEX AND ENZYME ACTION
There is no single theory which accounts for theunusual specificity and activity of enzyme catalysis.
However, there are a number of plausible ideas
supported by experimental evidence for a fewspecific enzymes.
Probably, all or some collection of these phenomenaacting together combine to give enzymes their
special properties.
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THE ENZYME-SUBSTRATECOMPLEX AND ENZYME ACTION
The x-ray crystallography, spectroscopy, andelectron-spin resonance showed the existence of asubstrate-enzyme complex.
The substrate binds to a specific region of theenzyme called the active site,where reaction occursand products are released.
Binding to create the complex is sometimes due to
the type of weak attractive forces.
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THE ENZYME-SUBSTRATECOMPLEX AND ENZYME ACTION
The complex is formed when the substrate key joinswith the enzyme lock.
The hydrogen bonds formed between the substrate
and groups widely separated in the amino acid chainof the enzyme.
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THE ENZYME-SUBSTRATE COMPLEXAND ENZYME ACTION
The protein molecule is folded in such a way that agroup of reactive amino acid side chains in theenzyme presents a very specific site to the substrate.
The reactive groups encountered in enzymes includethe R group of Asp, Cys, Glu, His, Lys, Met, Ser, Thr,and the end amino and carboxyl functions.
Since the number of such groups near the substrate
is typically 20, only a small fraction of the enzyme isbelieved to participate directly in the enzyme's activesite.
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Large enzymes may have more than one active site.
Many of the remaining amino acids determine thefolding along a chain of amino acids (secondary
structure) and the placement of one part of a foldedchain next to another (tertiary structure), which helpcreate the active site itself
THE ENZYME SUBSTRATE COMPLEX
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THE ENZYME-SUBSTRATE COMPLEXAND ENZYME ACTION
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Enzymes can hold substrates so that their reactiveregions are close to each other and to the enzyme'scatalytic groups.
This feature, which quite logically can accelerate achemical reaction, is known as theproximity effect.
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Reaction will occur only when the molecules come together atthe proper orientation so that the reactive atoms or groups arein close juxtaposition.
Enzymes are believed to bind substrates in especiallyfavorable positions, thereby contributing an orientation effect,
which accelerates the rate of reaction.
Also called orbital steering, this phenomenon has qualitativemerit as a contributing factor to enzyme catalysis. Thequantitative magnitude of its effect, however, is still difficultto assess in general.