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CHAPTER 4 : CHEMICAL COMPOSITION OF THE CELL

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LEARNING OUTCOMESTo state what enzymes are. To explain why enzymes are needed inlife processes.

To list the general characteristics of

enzymes. To relate the name of enzyme tosubstrate.

To state sites where enzymes aresynthesised.

To state the meaning of intracellularenzymes & extracellular enzymes.

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ENZYME & ITS REQUIREMENT IN LIVING

PROCESSES

Metabolism: biochemical processes in

the cells

Involves a series of chemical reactions(complex compound can besynthesised

from simple substances or broken down).Its control by enzymes.

ENZYMEs: organic catalyst that increase

the rate of a biochemical reaction

A proteins which function asbiocatalyst.

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Organisms depends on enzymes for thebiochemical processes in the cells

Enable biochemical reactions to take placequickly in the cells where the internalenvironment such as temperature may not

favourable for chemical reactions

Substrate: the substance that is actedupon by an enzyme.

Required for :

Digestion, synthesis of substances,contraction of muscles, respiration,etc.

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CHARACTERISTICS OF

ENZYMES1. Speed up the rate of biochemical

reactions. Increase the rate at which chemical rxns

occur

Much more efficient than inorganic

compound

1. Proteins produced by living cells

2. Not destroyed / changed by the rxn

3. Effective in small amount.4. The action is extremely specific.

Each rxn need its own specific enzyme

Each enzyme only act on one substrate

based on lock & key hypothesis.

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LOCK AND KEY HYPHOTESIS

Substrate molecule represent the KEY.

Enzyme molecule represent the LOCK.

Substrate molecule binds to the active site

to form an enzyme-substrate complex.

Enzyme catalyses substrate to formproducts.

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CHARACTERISTICS OF ENZYMES

(cont.)

6. Can work in either direction (reversiblerxn)

7. Denatured by high temperature 40-60oC denatured

Low temp. less active Optimum temp. 35-40oC

6. Sensitive to pH. Most active at pH7

Some enzymes require specific acidic(pepsin)/alkaline condition (trypsin)

6. Affected by inhibitors Inhibitors slow down/ stop enzyme activity

Examples : cyanide, lead & mercury

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CHARACTERISTICS OF ENZYMES

(cont.)10.Some enzymes require cofactors

Some enzymes only work in the presenceof other chemicals = cofactors

Examples : copper (II) ion (Cu2+), iron (II) ion(Fe2+) & vitamins

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NAMING OF ENZYMES By adding -ase to the main part of the

name of substrate on which they act. Examples :

Maltose maltase

Sucrose sucrase

Lactose lactase Protein protease

Lipids lipase

Amylum (starch) - amylase

Some enzymes which cannot be namedthis way because names of these enzymeshave been used for a long time. Examples : rennin, pepsin, erepsin, trypsin

SITES OF ENZYME

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SITES OF ENZYME

SYNTHESIS Made by protein synthesis within the

cells.

Located at the ribosomes in theprotoplasm of the cells.

Depends on the DNA code.

DNA RNA mRNA leaves the

nucleus enters into cytoplasm binds with the ribosomes RNAassembles the a.a into specificproteins modified to becomeenzymes.

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EXTRACELLULAR

ENZYMES Intracellular enzymes = producedby the cell & function within thecell.

Examples : enzymes that are involvedin respiration (mitochondria) & inphotosynthesis (chloroplast)

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Extracellular enzymes =secreted out of the cell &

functions outside the cell.

Examples : salivary amylase,trypsin, & lipase are producedin the pancreas & transportedto the duodenum.

Production of extracellularenzymes

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FACTORS AFFECTING

ENZYME ACTIVITY

pH level Protein are denatured by changes inthe pH level of the reaction medium.

Most enzymes are effective in only anarrow pH range.

The optimum pH : the particular pH atwhich the rate of reaction isfastest.

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Temperature

Low temperature, the rate of enzymereaction is low.

Temperature >, rate of reaction >. increasing the force & the rate of collision.

Low temp (below 40oC), a rise of 10oC willdouble the rate of reaction.

Optimum temp = 37oC @ body temperature.

Over 40oC, enzymes becomes denaturedrapidly

At 60oC, enzymes are denatured & thereaction stop.

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Concentration of Substrate pH value, temperature & enzyme

concentration are keptconstant, the rate of enzymereaction increases directly

proportional to the amount ofsubstrate present until alimiting value.

The rate of enzyme reactiondoes not increase even thoughthe [substrate] increase.

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Concentration of Enzyme pH value, temperature,

substrate concentration arekept constant.

Reaction increases directly

proportional to the [enzyme]until it reaches a limitingvalue.

Any increase in the enzyme

concentration does not increasethe rate of reaction.

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USES OF ENZYMES IN DAILY

LIFE & INDUSTRY

APPLICATIO

N

ENZYMES USES

Daily products Rennin

Lactose

To coagulate milk

proteins in cheeseproduction

To produce lactose-

free milk.

Meat industry Trypsin

Papain

To digest & tenderisemeat, which makes iteasier to cook the

meat & shortens

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APPLICATIO

N

ENZYMES USES

Bakingindustry

-amylaseTo breakdown starchflour into sugars inthe making of breads& buns.

Production offruit juices

-amylase

Amyloglucosidase

Glucoseisomerase

Pectinase

To produce fructosesyrup from cornstarch. Used as fooddrink sweeteners.

To digest the pectinin plant cells &increase the volumeof fruit juices.

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APPLICATIO

N

ENZYMES USES

Brewingindustry

-amylase

Zymase

To digest starch intosugars

To convert sugarsinto alcohol

Extraction ofagar frommarineseaweed

Cellulase To breakdown plantcell walls fromseaweeds. Makes iteasier to extract agarfrom seaweeds.

Biologicaldetergent

Amylase

Protease

Lipase

To be used in dishwashers & in washingpowders.

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APPLICATIO

N

ENZYMES USES

Leatherindustry

Protease To remove hair & tosoften leather tomake bags, belts &shoes.

Paperindustry

Amylase To digest starch intosmaller molecules tofill spaces betweencellulose fibres toproduce smoother

paper.Medicine Microbial trypsin To dissolve blood

clots

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APPLICATIO

N

ENZYMES USES

Geneticengineering

Ligase

Restrictionendonuclease

To produce GMO toincrease foodproduction,hormones &pharmaceutical

products.

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