10 -plant enzyme

8/19/2019 10 -Plant Enzyme

1/29

CHAPTER 10 ENZYME


2/29

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.


3/29

• 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


4/29

%f substrate and active site are complementary&the enzyme will catalyse.

substrate ! active site ' en(%)e*ubtrate

#o)ple+ ' productsSubstrate

Active site

Enzyme

Products


5/29

,. 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


6/29

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.


7/29

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.


8/29

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.


9/29

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


10/29

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


11/29

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


12/29

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


13/29

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)


14/29

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.


15/29

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


16/29

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.


17/29

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#


18/29

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 : ;


19/29

4owever& there are exceptions for certain enzymes

such as3 >epsin p4 ?.: ; 2.: *acidic+

Renin p4 @.: *alkaline+


20/29

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


21/29

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


22/29

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


23/29

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 ?


24/29

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


25/29

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


26/29

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


27/29

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


28/29

6.4 Tranerae

These enzymes catalyse the transfer of achemical group from one substrate to another

Example3

lucose glucose(6(phosphate

T> $>


29/29

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

10 -plant enzyme

Documents