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10 -Plant Enzyme
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Transcript of 10 -Plant Enzyme
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CHAPTER 10 ENZYME
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1. DEFINITION
Enzymes are globular protein. Enzymes lo!er t"e a#ti$ation energ% needed for
reaction take place.
Enzymes act as biologi#al #atal%t and pee& up
the rate of metabolic reactions. Enzymes are highly pe#i'# in action.
Enzymes possess a#ti$e ite and will only catalysereaction when substrate and active site havecomplementary shapes.
The enzyme combine with its substrate to form anen(%)e*ubtrate #o)ple+.
The complex then breaks up into pro&u#t andenzyme.
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• Every enzyme is specic for a particular reaction.• Every step in a metabolic pathway is catalysed by
a dierent enzyme.
• Reaction begins with reactants and end with
products.
! " # ! $
rea#tant pro&u#t
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%f substrate and active site are complementary&the enzyme will catalyse.
substrate ! active site ' en(%)e*ubtrate
#o)ple+ ' productsSubstrate
Active site
Enzyme
Products
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,. En(%)e Re&u#eA#ti$ation Energ%
%n a chemical reaction& the reactants must rstreach a high(energy intermediate state called thetranition tate before the products are formed
The amount of energy re)uired for reactants toreach the transition
state before
changing into
product is calledactivation energy
Activation energy with
enzyme
Progress of a reaction
E n e r g y o f s y
s t e m
Substrate
(reactants)
Transition state
Activation energy
without enzyme
Products (final state)
Figure
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Every chemical reaction involves the brea-ing andor)ing of chemical bonds.
"ond brea-ing re/uire external energ% while
bond or)ation releae energ%. Cataboli# reactions are reactions that releae
energ% e+ergoni#.
Anaboli# reactions are reactions that aborb
energ% en&ergoni#. The initial energy re)uired to break a bond is
referred to activation energy.
n enzyme provides an alternate reaction pathway.
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The enzyme can bind to the substrate *reactant+to form an enzyme(substrate complex whichcorresponds to the transition state.
The shape of the substrate is slightly changed&existing bonds are broken and new ones areformed.
This makes it easier for the substrate to bechanged into the product.
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2. Me#"ani) o en(%)ea#tion
ubtrate molecule bin& to an en(%)e molecule at its active site.
,orming an en(%)e*ubtrate #o)ple+.
The ubtrate is #on$erte& into pro&u#t whilestill being attached to the enzyme.
-nce reaction has occurred& the products arereleae& and the enzyme available to catalyseanother cycle of reaction.
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3. T%pe o en(%)e
1. Intra#ellular en(%)e
Enzymes that are produced in certain cellsand remain to react in the cell
These enzymes could exist either incytoplasm *in organelles+ or nucleus.
,. E+tra#ellular en(%)e
ome enzymes are produced by cell but thentransported out of the cell for action outsidethe cell
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4. C"ara#teriti#
1. En(%)e generall% a#t /ui#-l%
the speed of reaction is usually stated in/turnover number0 *refer to the number of
substrates+,. En(%)e are not &a)age&
however& this does not mean that enzymes canbe used repeatedly forever without replacement
2. En(%)e #an rea#t in bot" &ire#tion3. En(%)e are pe#i'#
each enzymes limited to one specic reactionthat involved one specic substrate only
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4. An en(%)e )ole#ule i uuall% bigger t"anit
ubtrate
5. All en(%)e are protein an& not all proteinare en(%)e
6.
En(%)e are #o)ple+ globular protein an&t"ree &i)enional.
Main un#tion o en(%)e
%ncrease the rate of chemical reaction bylowering activation energy
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Enzyme
(sucrase)
Active
site
1
2
3
Substrate
(sucrose)
Enzyme available
with empty active
site
Substrate
binds to
enzyme with
induced fit
Substrate is
converted to
products
4
roducts are
released
!lucose "ructose
1 Ho! anen(%)e
!or-
1 The enzyme is unchanged and can repeat the
process
Figure 5.6
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5. Me#"ani) o En(%)e
There are 2 main hypothesis explaining themechanism of enzyme action 3
The lock(and(key hypothesis
The induced(t hypothesis
7i)ple )e#"ani)
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4.1 8o#-*an&*-e%"%pot"ei
The hypothesis proposed that the active site andsubstrate are e+a#tl% #o)ple)entar%
n enzyme is a large globular protein with specic threedimensional shape.
%t has a site called the a#ti$e ite containing amino acid
that are complementary to the substrate. %n the lock(and(key hypothesis& the shape of theubtrate 9-e%: 't into t"e a#ti$e ite o t"een(%)e 9lo#-:; forming an enzyme(substrate complex
Reaction takes place and pro&u#t are formed andreleased.
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4., In&u#e&*'t "%pot"ei
%t is a modied version of the lock(and(key hypothesis The hypothesis suggested that active site is
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5. Fa#tor a=e#ting en(%)e
ny factors that aect the activity of an enzyme willchange the rate of the reaction catalysed by thatenzyme
Enzyme characteristic are aected by several factors temperature
p4
ubstrate concentration
enzyme concentration.
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5.1 T"e e=e#t oTe)perature
t lo!er temperature& enzymesare not a#ti$e
s the temperature rises& thesubstrate and the enzyme
molecules move rapidly and aremore likely to collide The in#reae in te)perature
to a specic level can in#reaet"e rate o t"e en(%)ea#ti$it% until the opti)u)
te)perature rate. Ater t"e opti)u)
te)perature the enzymesactivities &e#reae& and totallystopped at temperature of567o#
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5., T"e e=e#t o pH
ll enzymes have a specicoptimum p4 at which they functionmost e8ciently
9ost enzyme act at a p4 in rangeof : ;
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4owever& there are exceptions for certain enzymes
such as3 >epsin p4 ?.: ; 2.: *acidic+
Renin p4 @.: *alkaline+
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5.2 T"e e=e#t o En(%)eCon#entration
The rate of an enzyme(catalysed reaction is &ire#tl%proportional to the concentration of the enzymes ifsubstrates are present in excess concentration and
no other factors are limiting
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5.3 T"e e=e#t o 7ubtrateCon#entration
%ncreasing the substrate concentration can give anincrease in reaction rate
t lower concentrations the rate increase in directproportion to the substrate concentration
t higher substance
concentration the rate of
reaction becomesconstant
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6. Clai'#ation o En(%)e
9any enzymes have a name derived from thename of their substrate& with the ending –aseadded. Example& lactase hydrolyse lactose
-ther enzymes have been given less informativenames. Example include many of the enzyme ofdigestion& such as pepsin& renin
ystematic naming of enzymes is based on an
agreed classication of enzyme and on thename of the substrate of the reaction catalysed
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Enzymes can be classied by the kind ofchemical reaction catalyzed3
?. 4ydrolase
2. Ayase
B. %somerase
C. Aigase:. Transferase
6. -xidoreductase
This classication system introduced in ?
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6.1 H%&rolae
These enzyme catalyse the hydrolysis of asubstrate by the addition of water
Example3
Aipase& amylase& sucrase& peptidase
ucrose ! water glucose! fructose
sucrase
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6., 8%ae
These enzyme catalyse the breaking of chemicalbonds without the addition of water
Example3
>yruvate decarboxylase ; decarboxylation ofpyruvic acid
>yruvate ethanol !
carbon dioxide
Pyruvate decarbo!ylase
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These enzyme catalyse the rearrangement of atomswithin a molecule converting one isomer to another
Example3
lucose(?(phosphateglucose(6(phosphate
6.2 Io)erae
"hos"hoglucoisomerase
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6.3 8igae
These enzymes catalyse the Foining together oftwo molecules with the simultaneous hydrolysisof T>
Example3
amino acid ! specic tRG ! T>amino acid(tRG complex ! $> ! >i
synthetase
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6.4 Tranerae
These enzymes catalyse the transfer of achemical group from one substrate to another
Example3
lucose glucose(6(phosphate
T> $>
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6.5 O+ire&u#tae
These enzyme catalyse redox reactions*biological oxidation and reduction reactions+ bythe transfer of hydrogen& oxygen or electron fromone molecule to another
Example3
-xidase catalyses the addition of oxygen tohydrogen& forming water
lucose ! oxygen gluconicacid ! water
#lucose o!idase