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CHAPTER 4 : CHEMICAL COMPOSITION OF THE CELL

4.1 The Chemical Composition o the Cell

Elements in the cell

The cells of living organisms composed of elements.

Element a substance composed of only 1 kind of atom (cannot be broken down into simpler

substances by chemical reactions).

!" essential elements(bioelements)

a# 96 ! "# $# % & ' (most compounds in the cell consist of ")

$# ! "a# # *# +# 'a# "l# ,g# -e

n human body# the main elements are $/(60)# " (1.0)# %/(9.0) & ' (2.2).

T%ace elements("u# # -e ! 3 4.41 of the body mass) needed in very small amounts (critical

in maintaining healthy cells)

F&nctions o elements in animal ' plant cells

ElementF&nctions

Animal cells Plant cells

H( C( O( N +ynthesis of organic compounds (proteins# lipids# nucleic acids)S "omponent of some proteins.

Na 5egulates osmotic pressure in

cells

Transmit nerve impulses

'ot reuired

M) *rotein synthesis

"ofactor for en7ymes +ynthesis of chlorophyll

8ctivates en7ymes

Ca -ormation of strong bones & teeth

"ontraction of muscle cells

lood clotting

+ynthesis of cell walls (cellulose)

,aintain semi!permeability of

plasma membrane

Fe *i%on# +ynthesis of haemoglobin

+ynthesis of respiratory en7ymes +ynthesis of chlorophyll

8s an electron carrier during

photosynthesis & respiration

P +trong bones & teeth

"ontraction of muscle cells

+ynthesis of 8T* & energy carrier

:ssential component of nucleic acids

(;'8 & 5'8)

-ormation of flowers & seeds

*romotes cell division

+ynthesis of 8T* & nucleic acids

+ ,uscle contractions & transmission +ynthesis of carbohydrates

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of nerve impulses. 8ctivates certain en7ymes

Cl +ynthesis of hydrochloric acid by

the gastric glands (stomach) whichdestroy pathogens & maintain p% of

the stomach

*hotolysis of water during light

reaction in photosynthesis.

Chemical compo&n,s in the cell

Compo&n, substances composed of / or more elements

/ ma

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8re macromolecules

"ontains "# %# $# ' and *

+tore & transmit genetic information

asic units are nucleotides. :ach nucleotides consists of 2 parts =

a) 8 nitrogenous base

b) 8 pentose sugar (0!" sugar deo>yribose or ribose)

c) 8 phosphate group.

/ types of nucleic acids=

a) deo>yribonucleic acid (;'8)

b) ribonucleic acid (5'8)

-NA

a) 8 double!stranded nucleic acid (/ strands of polynucleotides twisted around each otherto form ,o&$le heli)

b) +ugar!phosphate strands are on the outside# the nitrogenous bases are on the inside

held together by H $on,s.

c) -ound in nucleus# mitochondrion & chloroplast

d) s the genetic material that organisms inherit fr their parents

e) s structure allows it to store genetic information & pass the genetic code to new cells

RNA

a) -ound in cytoplasm# ribosomes & nucleus

b) "onsists of a single!stranded nucleotide# which may be folded back on itself

c) 2 types of 5'8 in the cells

d) The three types of 5'8 are involved in protein synthesis (m5'8). m5'8 carries ;'8

genetic code into the cytoplasm & direct the synthesis of proteins.

e) s also the genetic material for some viruses

The impo%tance o /ate% in the cell

1) %uman body consists of @4 water.

/) Aater presents in living cells# lymph# blood plasma & interstitial fluid.

2) Aater is a polar molecule (uneual distribution of charges each molecule has a positive end &

a negative end. The % end of the water molecule is slightly Bve# while the $ end is ve).

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) ecause of this property# water can dissolve many ionic compounds (mineral salts & polar

sugars)

0) The water molecule is CD!shapedE.

6) mportance of water =

a# me,i&m o% $iochemical %eactions

%/$ is eliminated during the synthesis of proteins# lipids & sugars

%/$ involved in the breaking down of proteins# lipids & carbohydrates in the food

we eat.

:n7ymatic reactions reuire %/$.

$# maintain the $o,0 tempe%at&%e

%/$ helps to distribute heat in the body. :>cess heat is eliminated through

perspiration# urination & defaecation.

:vaporation of sweat dissipates body heat & cools the body surface.

:vaporation of %/$ fr plants (transpiration) keep plant tissues cool.

c# Solent

%/$ is the universal solvent

8 versatile solvent because of polarity of its molecules

onic & polar molecules can dissolve in %/$

,# p%oi,e moist&%e

*rovide moisture to respiratory surfaces (alveoli)2 enables respiratory gases to

dissolve in them before diffusion across the respiratory surfaces

e# maintain osmotic $alance ' t&%)i,it0

n animals# the F G of dissolved inorganic salts in %/$ is important in maintaining the

osmotic balance between the blood & interstitial fluid.

n plants# the cell sap in the vacuole contains % /$. 8 high osmotic F G in plant cells

encourages %/$ to enter the cells. This causes the cell to be turgid (provide

support).

# hi)h s&%ace tension ' cohesion

%/$ molecules have very high cohension.

%/$ can move in long# unbroken columns through the >ylem tissue (maintain a

continuous flow of %/$ up the stem of the leaves.

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)# p%oi,e s&ppo%t

support the structure of a cell (94 of protoplasm made up of % /$)

h# l&$%ication

,ucus & synovial fluid consist mainly of %/$

,ucus assists the movement of food

i# t%anspo%t me,i&m

lood plasma contain 94 of %/$. t contains sugars# amino acids# $/& "$/which

dissolve in %/$

Aaste products (urea) are e>creted fr the body in the urine.

4.! Ca%$oh0,%ates

1. "arbohydrates consist of "# % & $

/. %=$ ratio H /=1

2. 2 main types of carbohydrates =

a) monosaccha%i,es(simple sugars glucose# fructose# galactose)

b) ,isaccha%i,es(comple> sugars maltose# sucrose# lactose)

c) pol0saccha%i,es(starch# cellulose# glycogen)

A# Monosaccha%i,es *simple s&)a%#

8re monomers (small molecules that build a polymer) of carbohydrates.

The simplest carbohydrates.

"annot be broken down into smaller units.

8re the basic sub!units of comple> carbohydrates.

8re reducing sugars (as reducing agent in enedictIs test)

! enedictIs test used to detect the presence of reducing sugars.! enedictIs solution blue contains copper () sulphate

! ,onosaccharides reduce the copper () sulphate to form brick!red precipitate of

copper () o>ide.

Jlucose (grape sugar)

! "6%1/$6

! s the end product in the digestion of starch (rice & bread)

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! s the monomer where most polysaccharides are made

-ructose (sweet fruits & honey)

Jalactose (milk)

?ong!chained monosaccharides B proteins H glycoproteins

?ong!chained monosaccharides B lipids H glycolipids

3# -isaccha%i,es *comple s&)a%#

"onsists of / monosaccharides

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,altose (malt sugar)

! made up of / glucose molecules

! a product of the partial digestion of starch

! used in brewing of beer

C# Pol0saccha%i,es

8re polymers formed by condensation of glucose monomers.

nsoluble in %/$ (large molecular si7e)

;o not taste sweet & do not crystalli7e

"an be h0,%ol05e,or broken down into smaller molecules by adding diluted acids & boiling

through en7ymatic reactions.

Sta%ch! found in wheat# rice# potatoes# bread & corn

! the energy storage compounds in plants

! iodine test (test for the presence of starch in leaf. f starch is present# the iodine

solution change fr brown blue!black)

6l0co)en

! main reserve of carbohydrates in animals & yeast

! stored in liver & muscle cells

Cell&lose

! plant cell walls are made of

! provides support for plant cells

4.7 P%oteins

"omple> organic molecules

,ade up of "# %# $# '# +# *

-ish# meat# milk# nuts# eggs

8ll proteins are made up of one K more polymers (polypeptides)

Impo%tance o p%oteins:

a) 8s building blocks for many structural components of the cell (for growth)

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b) -orm en7ymes (cataly7e biochemical reactions)

c# -orm hormones (control growth & metabolism)

,# -orm antibodies (attack & destroy invading pathogens)

Pol0pepti,es

! made up of hundreds or thousands of amino acids (monomers)

-ipepti,e

! consists of / molecules of amino acids linked together by peptide bond

(condensation). 1 water molecule is eliminated.

! "an be broken down into amino acids through hydrolysis

! -urther condensation can link more amino acids to the dipeptide to form

polypeptide chain.

8mino acid B amino acid dipeptide B %/$ *con,ensation#

;ipeptide B %/$ amino acid B amino acid *h0,%ol0sis#

T0pes o amino aci,s

e# -irst class proteins (animal proteins) contain all the essential amino acids needed by the

body

# +econd class proteins (plant proteins) do not contain all the essential amino acids

)# / groups of amino acids=

a) essential amino acids

b) non!essential amino aci,s

h# Essential amino aci,s

! cannot be synthesi7ed by the body

! can only be obtained fr a healthy diet

! 9 essential amino acids ! leucine

i# Nonessential amino aci,s

! can be synthesi7ed by the body

! 11 non!essential amino acids

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P%otein St%&ct&%es

different levels of protein structure=

a# P%ima%0 st%&ct&%e

?inear seuence of amino acids in a protein molecule (polypeptide chain)

%ormone insulin

$# Secon,a%0 st%&ct&%e

*olypeptide chain coiled or folded to form an alpha!heli> (L!heli>) & beta!pleated (M!

pleated) sheets.

The L!heli> and M!pleated sheet structures are held together by hydrogen bonds.

c# Te%tia%0 st%&ct&%e

The L!heli> and M!pleated sheet are folded K coiled into 2!dimensional shape.

The structure is maintained by ionic# disulphide & hydrogen bonding. %ormones# en7ymes# plasma protein# antibodies# myoglobin.

,# 8&ate%na%0 st%&ct&%e

/ or more tertiary structure polypeptide chains are arranged to form a functional &

comple> protein molecule.

%aemoglobin

4.4 Lipi,s

8re organic compounds N carbon# hydrogen# o>ygen

%=$ H larger than the /=1 ratio in carbohydrates ( of $/in lipids is lower than in

carbohydrates)

+ome lipids contain phosphorus & nitrogen

8re non!polar molecule insoluble in water# dissolve in other lipids & non!polar solvents (ether

& ethanol)

,ain types of lipids=

a) fats & oils (triglycerides)

b) wa>es

c) phospholipids

d) steroids

importance of lipids=

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a) store energy for long terms

b) act as sources of energy

c) ma

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-ie%ences

Sat&%ate, ats 9nsat&%ate, ats

8nimal fats (lard)# red meat# coconut oil#

palm kernel oil# full cream milk & butter.

Degetable oils (corn oil# olive oil &

soybean oil).

-atty acids in saturated fats do not

have double bonds between " atoms. -atty acids in unsaturated fats have at

least 1 double bond between " atoms.

The " atoms are bonded to the ma> no

of other atoms. % % % %

! " " " " !

% % % %

The " atoms are not bonded to the ma>

no of other atoms.% % % %

! " " H " " !

% %

"annot any chemical bonds with other

atoms or react with additional hydrogenatoms (all the bonds between " atoms

have the ma> no of hydrogen atoms)

8ble to react with additional hydrogen

atoms

Pnsaturated fats with one double bond

are called mono&nsat&%ate, ats

Pnsaturated fats with twoKmore double

bonds are called pol0&nsat&%ate, ats

8re solids at room temperature. 8re liuids at room temperature.

5aises the levels of ?;? (bad

cholesterol) in the blood. ncrease the level of %;? (good

cholesterol) to ?;? & lowers the levelsof total cholesterol & ?;? in the blood.

$# aes

8re long!chained molecules (cause wa>es to be waterproof)

8re similar to triglycerides# but the fatty acids are bonded to long!chain alcohols rather than

glycerol.

8re produced by both plants & animals

Psually hard solids at room temp.

-ound on cuticles of the epidermis of leaves# fruits & seeds.

+ebum that is e>creted from the oil glands in the skin contains wa> that soften the skin. mportance of wa>es=

! used to waterproof the e>ternal surface of the plants & animals.

! "uticle of leaf

! *rotective covering on an insectIs body

! 8 constituent of the honeycomb bees.

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c# Phospholipi,s

8re the main components of plasma membrane.

"ontrol the permeability of plasma membrane.

%ave a structure similar to triglycerides but one of the 2 fatty acid molecules is replaced by a

phosphate group.

The end of the phospholipid molecule containing the phosphate group is h0,%ophilic */ate%

loin)#. The other end containing the hydrocarbon chains of the fatty acids is h0,%opho$ic

*/ate%hatin)#.

%ydrophilic head / hydrophobic fatty acid tails

The hydrophilic end to the phospholipid molecule is soluble in water# while the hydrophobic

end is insoluble in water.

,# Ste%oi,s

+teroid molecule has a comple> ring structure.

$ccur in plants & animals.

ncluded cholesterol & se> hormones (testosterone# oestrogen# progesterone).

"holesterol is the ma

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4." En50mes

+tudy of en7ymes en7ymology

:n7ymes

! are proteins (act as biological catalysts)

! speeds up biochemical reactions in the cell but remain unchanged at the end of the

reactions.

The reactant in an en7ymatic reaction is called a s&$st%ate# the substance formed at the end

of the reaction is called p%o,&ct.

:n7yme+ubstrate products

,any biochemical processes occur in a cell simultaneously at all times N metabolism

,etabolism includes =

a) anabolism metabolic reactions that build comple> molecules (photosynthesis)

b) catabolism metabolic reactions that break down comple> molecules (digestion &

respiration)

Aithout en7ymes# these biochemical reactions would be too slow to sustain life.

6ene%al cha%acte%istics o en50mes

1. All en50mes a%e p%oteins

:n7ymes are synthesi7ed by living organisms.

!. En50mes spee, &p the %ate o $iochemical %eactions

:n7ymes are not affected by the reactions they catalyse.

:n7ymes are not changed or destroyed by the reactions.

:n7ymes increase the rate at which chemical reactions occur in cells.

8re much more efficient than inorganic catalysts.

7. En50mes a%e not ,est%o0e, $0 the %eactions /hich the0 catal0se

"an be used again.

4. En50mes a%e nee,e, in small amo&nts

:n7ymes are used up but released at the end of the reaction.

8 small uantity of en7yme can bring about a large amount of biochemical reaction.

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$ne molecule of en7yme can turn thousands or millions of substrate molecules into

products per minute.

". En50mes can /o%; in eithe% ,i%ection

:n7yme!catalysed reactions are reversible.

5eaction can proceed from left to right K from right to left

. En50mes a%e sensitie to pH

-or every en7yme# there is an optimum p% at which it function best.

+mall changes in p% of the medium will denature the en7yme & render it inactive

(alternations in the ionic charges of the acidic & basic groups of the en7yme change the

shape of the en7yme)

?. En50me actiities can $e slo/e, ,o/n o% completel0 stoppe, $0 inhi$ito%s

-or e>amples# heavy metals ( lead & mercury)

nhibitors are substances that slow down K stop en7yme activity.

1@. Some en50mes %e&i%e coacto%s

+ome en7ymes only work in the presence of other chemicals (cofactors)

"ofactors bind to the en7ymes & help to weaken the bonds in the substrate molecules.

-erum & copper (inorganic cofactors)# water!soluble vitamins vit comple> (organic

cofactorsK coen7ymes)

Namin) o en50mes

;erived from the name of the substrate it catalyses.

8dding the suffi> !ase to the name of the substrates they hydrolyse=

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?actose (substrate) lactase (en7yme)

+ucrose (substrate) sucrase (en7yme)

?ipid (substrate) lipase (en7yme)

:n7yme is written above the reaction arrow.

sucrase

+ucrose B water glucose B fructose

Int%acell&la% ' et%acell&la% en50mes

:n7ymes are synthesi7ed by specific cells.

:n7ymes can be divided into / groups=

a) intracellular en7ymes

b) e>tracellular en7ymes

Int%acell&la% en50mes :

! produced & retained in the cells

! can be found in cytoplasm# nucleus# mitochondria & chloroplasts.

! :g = catalase & phosphorylase

Et%acell&la% en50mes :

! produced in the cell but secreted from the cell to function e>ternally

! eg = digestive en7yme (amylase & lipase) produced by the pancreas transported to theduodenum (for en7ymatic reaction)

S0nthesis o en50mes

+ince en7ymes are made of proteins# they are synthesi7ed by ribosomes.

ntracellular en7ymes are synthesi7ed on CfreeE ribosomes.

:>tracellular en7ymes are synthesi7ed on ribosomes attached to endoplasmic reticulum.

1. The information for the synthesis of en7ymes is carried by the ;'8 (the seuences of

bases on the ;'8 are codes to make proteins).

/. n the nucleus# the ;'8 double heli> unwinds & e>poses its / strands for the synthesis of

m5'8 (messenger 5'8). The m5'8 is synthesi7ed according to the instruction on the

;'8.

2. The m5'8 then leaves the nucleus & moves to a ribosome.

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. The m5'8 attaches itself to the ribosome located on the :5.

0. 8s the ribosome moves along the m5'8# it reads information encoded within the m5'8.

6. The information is translated into a specific polypeptide chain which forms the en7yme.

@. Ahen the en7yme synthesis has been completed# it is transported through the space

within the rough :5.

. The en7yme that depart from the rough :5 wrapped in a transport vesicle (is the bud off

from the membranes of rough :5).

9. The transport vesicle fuses with the membrane of Jolgi apparatus# releasing the en7yme

into the Jolgi apparatus.

14. n the Jolgi apparatus# the en7yme is further modified before being packed in a secretory

vesicle.

11. The secretory vesicle transports the en7yme to the plasma membrane.

1/. The secretory vesicle membrane fuses with the plasma membrane & the en7yme is

released outside the cell.

The mechanism o en50me action

:ach en7yme molecule has a region with a very precise shape called the actie site.

The substrate molecule fits into the active site of the en7yme like a ;e0 into a loc;(highly

specific).

Loc; ' ;e0 h0pothesis

a) The substrate molecule is represented by the SkeyI

b) The en7yme molecule is represented by the SlockI.

c) The substrate molecule binds to the active site to form an en50mes&$st%ate comple

(key fits into a lock)

d) The en7yme catalyses the conversion of the substrate to product(s). $nce formed# the

products no longer fit into the active site & escape into the surrounding# leaving the active

site free to bind to more molecules of substrate.

The Bloc; ' ;e0 h0pothesis eplain that=

a) why en7ymes are specific

b) why any change in the shape of an en7yme alters its effectiveness

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en7yme B substrate en50mes&$st%ate comple en7yme B products

Facto%s aectin) the actiit0 o en50mes

1. Tempe%at&%e

8t low temp# the en7yme!cataly7ed reaction progress slowly. This is because the substratemolecules are moving at a relatively slow rate.

8s the temp increases# the rate of reaction increase=

! collisions between the substrate & en7yme molecules occur more freuently

! the random movement of molecules & more freuent collisions between the substrate &

the en7yme molecules increase the chances of the substrate molecules coming into contact

with the active sites of the en7yme.

:very 14O" rise in temp. the rate of en7ymatic reaction in a cell is doubled.

The rate of reaction increases up to a ma> at the optim&m temp.

! the optimum temp is the temp at which an en7yme cataly7ed a reaction at the ma %ate

! most en7ymes in humans & animals have an optimum temp at 2@O"

8bove the optimum temp# the rate of reaction decrease sharply until it stops completely at

64O"

! the bonds maintaining the structure of the en7yme start to break & the active site loses

its shape.

! the substrates can no longer fit into the active sites of the en7yme. The en7yme is said to

be ,enat&%e,.

-enat&%ationof en7ymes is irreversible. t is important for the body to maintain its temp at

an optimum level.

,ost organisms cannot survive at temp above 4O". +ome organisms# bac# live in hot springs

have optimum temp between 4O " & 144O "

!. pH

:n7ymes is affected by the acidity & alkalinity.

8 slight change in p% can have an adverse effect on the rate of en7yme!catalysed reactions.

Optim&m pHis the particular p% at which the rate of reaction is fastest.

n a cell# most en7ymes function optimally at a p% that ranges from 6 to .

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;eviations from the optimum p% decrease the rate of reaction because the bonds maintaining

the tertiary shape of this en7yme are broken.

The active site loses its shape & the en50mes&$st%ate complecan no longer be formed.

The en7yme is ,enat&%e,.

The effect of p% is normally reversible. 5estoring the p% to the optimum level usually

restores the rate of reaction.

*epsin found in the stomach acidic medium (p% /)

Trypsin found in the duodenum alkaline medium (p% .0)

7. S&$st%ate concent%ation

The rate of an en7yme!catalysed reaction increases in direct proportion to the s&$st%ate

concent%ationuntil the reaction reaches a ma %ate. eyond the ma> rate# the active sites of the en7yme molecules are fully occupied by the

substrate molecules.

The rate %emains constant. The en7yme molecules are said to be saturated & the reaction

has reached its ma> rate# Dma

ncrease the substrate concentration further has no effect on the rate of reaction.

The concentration of en7yme becomes a limitin) acto%. The only way to increase the rate of

reaction is by increasing the concentration of en7yme.

4. En50me concent%ation

The rate of an en7yme!catalysed reaction increases when the en50me concent%ationis

increased# as long as =

a) no other factors are limiting the rate of reaction

b) the substrate molecules available are in e>cess (more active sites are available for en7yme

action)

The rate of an en50mecatal0se, %eactionis ,i%ectl0 p%opo%tionalto the concentration of

the en7yme present until a ma %ateis achieved.

eyond the ma> rate of reaction# the concentration of substrate becomes a limitin) acto%.

Ahen the en7yme concentration is doubled# the rate of reaction per unit time will be doubled

as long as the substrates are present in e>cess concentration.

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The &ses o en50mes in ,ail0 lie ' in,&st%0

The use of en7ymes in industrial processes is known as en50me technolo)0.

:n7ymes can be obtained fr plants# animals# microorganisms (bac & fungi).

:n7ymes are widely used as detergents# floor cleansers# carpet shampoo# shoe deodori7er &

drain openers. These chemicals contain a combination of proteases# lipases# cellulose &

amylase.

:n7ymes are used in the te>tile# leather & food industries.

Application En50me 9ses

;airy industry Lipase 5ipening of cheese

Rennin +olidifies milk proteins

Lactase %ydrolysis of lactose to glucose & galactose (making of ice!

cream)rewing industry P%otease(

am0lase(

cell&lose

reakdown of starch & proteins# prevent cloudiness instored beers

iologicaldetergents

P%otease(

lipase( am0lase

5emoval of organic stains (gravy# oil & saliva)

aking industry Am0lase "onverts starch flour into sugar in the making of bread

P%otease reakdown of proteins

6l&cose oi,ase +tability of dough

,eat industry P%otease( papain Tenderi7ing of meats

Te>tile industry Am0lase 5emoval of starch applied to the threads of fabrics

AashingpowderKdetergent

P%otease(

am0lase

;issolve protein & starch stains in clothes

?eather industry P%otease 5emoval of hairs from hides

*aper industry Li)ninase 5emoval of lignin from pulp

+tarch industry Am0lase 'am0lo)l&coi,ase

"hange starch to sugar in the making of syrup

6l&cose

isome%ase

*roduction of high fructose syrup (glucose converted tofructose. -ructose is much sweeter than glucose# therefore

widely used in sliming products in small amounts)-ish industry P%otease 5emoves the skin of fish

8lcoholic drinks(beerKwine)

0mase "onverts sugars into ethanol

"ereal grainindustry

Cell&lase reakdown cellulose & removes seed coats from cerealgrains

+eaweed industry Cell&lase :>tracts agar from seaweed

*harmaceutical &medical industries

L0so50me 8ntibiotic

T%0psin 5emoval of dead tissues from wounds & burns

9%o;inase ;issolves blood clots after heart attack

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4.< The impo%tance o chemical composition in cells

n cells# various types of chemical substances are important of enable the cells to function

optimally.

1. Ca%$oh0,%ates

a) glucose

+torage of energy in plant & animal cells.

"ells would lack energy to carry out life processes

b) starch

+torage of energy in plant cells.

"ells would lack energy to grow & divide (seed germination)

c) glycogen

+torage of energy in animal cells.

?iver & muscle cells would not be able to carry out high metabolic activities.

d) cellulose

Jives structural support to the cell walls.

*lant cells would lose their shapes. The cells would burst when water enters by osmosis.

!. P%oteins

a) microfilaments

8ssociated with muscle contraction.

,uscle cells would be unable to contract.

b) microtubules

-ormation of cilia & flagella

Pnicellular organisms (*aramecium& :uglena) would be unable to move.

c) pore proteins & carrier proteins Transportation of ions across the plasma membrane.

ons would be unable to enter K leave the cell

d) haemoglobin

"arrier of o>ygen

5ed blood cells would be unable to carry o>ygen

e) antibodies

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mportant in defence against infectious diseases & in developing immunities

"ells would be invaded by pathogens (bac & viruses)

f) hormones

"auses changes to the metabolic reactions of cells

"ells would be unable to control metabolic reactions

7. Lipi,s

a) phospholipids

mportant constituent of cell membranes

There would be no cell membranes. Aater & all other substances could enter & leave the

cells freely

b) wa>es

Aaterproofing material

"ells in leaves# fruits & seeds would lose e>cessive water

c) fats & oils

"ertain unicellular auatic organisms produce an oil droplet to aid buoyancy

These unicellular auatic organisms would not be able to float

d) steroids

"holesterol strengthens the cell membranes at high body temp ,anufactures vit ; & se> hormones

"ell membranes would be weak

"ells would not be able to produce vit ; & se> hormones

. :n7ymes

"atalysed the rate of biochemical reactions in cells

iochemical reactions would be too slow to sustain lives of cells