AS BiologyAS Biology

Biological moleculesBiological molecules

OBJECTIVESOBJECTIVES

All shouldAll should : be able to describe the structure of a : be able to describe the structure of a water molecule,the H bonds that hold them water molecule,the H bonds that hold them together & and understand this is responsible for together & and understand this is responsible for its unusual properties. Be able to describe some its unusual properties. Be able to describe some of the properties of water and link some to its of the properties of water and link some to its structure and importance to living organismsstructure and importance to living organisms

Some maySome may: be able to take this a stage further : be able to take this a stage further and give detailed explanations of how the H and give detailed explanations of how the H bonds in water control the properties that are so bonds in water control the properties that are so important for living organismsimportant for living organisms

Unit 2 Module 1 Biological molecules

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Unit 2 Module 1 Biological molecules

Proteins enzymes

structural proteins

lipids

transport protein

phospholipids

triglycerides cholesterol

carbohydrates

saccharides

polysaccharides

structural

storage

water

nucleic acids

DNA

RNA

The Elements of lifeThe Elements of life 92 naturally occurring elements92 naturally occurring elements The atoms of only 16 are commonly found in living The atoms of only 16 are commonly found in living

organismsorganisms 4 account for 99% of the atoms found in living 4 account for 99% of the atoms found in living

organisms,these are in order of abundance:organisms,these are in order of abundance: HH hydrogen hydrogen C C carbon carbon OO oxygen oxygen NN nitrogen nitrogen This is because living organisms are made up of This is because living organisms are made up of

organic moleculesorganic molecules Others are Others are

calcium(Ca),iron(Fe),potassium(K),sodium(Na), calcium(Ca),iron(Fe),potassium(K),sodium(Na), chlorine(Cl),sulphur(S) & magnesium(Mg)chlorine(Cl),sulphur(S) & magnesium(Mg)

BondingBonding Atoms are joined Atoms are joined

together to make together to make molecules and molecules and compoundscompounds

This is done by This is done by chemical chemical bondsbonds

Most of the molecules Most of the molecules making up living making up living organisms have atoms organisms have atoms joined by joined by covalent bondscovalent bonds

Covalent bonds are Covalent bonds are shown by lines.They can shown by lines.They can be single,double or be single,double or treble.They are formed treble.They are formed by by sharing electronssharing electrons

Glycine – an amino acid

Covalent bondingCovalent bonding Carbon always has 4 covalent bonds Carbon always has 4 covalent bonds

with other atoms. Terrestrial life forms with other atoms. Terrestrial life forms are carbon based. This multiple bonding are carbon based. This multiple bonding allows carbon to be a allows carbon to be a framework atomframework atom

All the biological molecules we will learn All the biological molecules we will learn about use carbon as a framework atom.about use carbon as a framework atom.

Other bonds formed are: Oxygen Other bonds formed are: Oxygen 2 ,hydrogen 1 & nitrogen 32 ,hydrogen 1 & nitrogen 3

ethanol

ethene

Covalent bondingCovalent bonding

The building blocks of The building blocks of lifelife

Living organisms are mainly made up of Living organisms are mainly made up of macromolecules macromolecules (giant molecules)(giant molecules)

These are These are polymers polymers made up of many made up of many smaller smaller monomers monomers by a process calledby a process called polymerisationpolymerisation

The main macromolecules are:The main macromolecules are: PolysaccharidesPolysaccharides Nucleic acidsNucleic acids Proteins (polypeptides)Proteins (polypeptides) Lipids (fats)Lipids (fats)

The Building Blocks of The Building Blocks of lifelife

MONOMERMONOMER POLYMER POLYMER

monosaccharide

Organic base, sugar & phosphate

Amino acids

Fatty acids & glycerol

polysaccharide Nucleic acids proteins

lipids

nucleotides

CarbohydratesCarbohydrates All contain the elements carbon, hydrogen & All contain the elements carbon, hydrogen &

oxygenoxygen The name comes from hydrated carbon!The name comes from hydrated carbon! For every carbon atom there is a waterFor every carbon atom there is a water General formula for carbohydrate is General formula for carbohydrate is CCnn(H(H22O)O)nn Q. Fructose has 6 carbons, what is it formula? Q. Fructose has 6 carbons, what is it formula?

What about ribose which is a pentose sugar?What about ribose which is a pentose sugar? There are There are 2 types of carbohydrate2 types of carbohydrate: : 1. Simple sugars: Monosaccharide & 1. Simple sugars: Monosaccharide &

DisaccharidesDisaccharides 2. Polysaccharides2. Polysaccharides

Simple sugars: Simple sugars: MonosaccharidesMonosaccharides

Sugars – all end in Sugars – all end in -ose-ose White,crystalline substances,dissolve easily White,crystalline substances,dissolve easily

in water to give sweet solutions.in water to give sweet solutions. Single sugar molecule – mono = oneSingle sugar molecule – mono = one General formula (C HGeneral formula (C H22O)n where n is the O)n where n is the

number of carbon atomsnumber of carbon atoms So if So if 6 carbon atoms6 carbon atoms(a hexose sugar) the (a hexose sugar) the

molecular formulamolecular formula is is CC66HH1212OO66

What about pentose sugars(C5) or triose What about pentose sugars(C5) or triose sugars(C3)?sugars(C3)?

GlucoseGlucose Most important and Most important and

widespread widespread monosaccharide.monosaccharide.

Hexose sugarHexose sugar The 6 carbons are The 6 carbons are

numbered numbered Function:Transported Function:Transported

around in the blood and around in the blood and used in cells as a source used in cells as a source of energy in respiration. of energy in respiration. The energy is released The energy is released in the form of ATPin the form of ATP

Structural formula

Molecular formula C6H12O6

1

2

3

4

5

6

The ring form of glucoseThe ring form of glucose

The chain of carbons The chain of carbons in hexose(and in hexose(and pentose) sugars is pentose) sugars is long enough to long enough to close close upup and form a more and form a more stable ring stable ring structurestructure

Carbon atom Carbon atom 11 joins joins to the oxygen on to the oxygen on carbon atomcarbon atom 5 5

Glucose isomersGlucose isomers

The new OH formed in the reaction can be The new OH formed in the reaction can be above the ring - above the ring - β glucoseβ glucose or below - or below - α α glucoseglucose

These are These are isomersisomers-two forms of the same -two forms of the same chemical.chemical.

Triose,pentose & Triose,pentose & hexose sugarshexose sugars

Roles of Roles of monosaccharides in monosaccharides in

living organismsliving organisms A source of energy for respiration.A source of energy for respiration. Due to large number of C-H bonds which when Due to large number of C-H bonds which when

broken release a lot of energybroken release a lot of energy This energy is used to make ATP(adenine This energy is used to make ATP(adenine

triphosphate) from ADP(adenine diphosphate)triphosphate) from ADP(adenine diphosphate) Also used as building blocks to make larger Also used as building blocks to make larger

molecules for example:molecules for example: Deoxyribose(pentose) used to make DNADeoxyribose(pentose) used to make DNA Ribose used to make RNA and ATPRibose used to make RNA and ATP Glucose makes up starch,cellulose and glycogen.Glucose makes up starch,cellulose and glycogen.

Disaccharide formationDisaccharide formation

Two glucose molecules are held close together by an Two glucose molecules are held close together by an enzyme.enzyme.

Water is lost and a 1-4 Water is lost and a 1-4 glycosidic bond(linkglycosidic bond(link) formed .) formed . This is a This is a condensation reactioncondensation reaction The new molecule is a disaccharide - The new molecule is a disaccharide - maltosemaltose

A disaccharide - maltoseA disaccharide - maltose

1-4 glycosidic link

Common DisaccharidesCommon Disaccharides

Hydrolysis of maltose – by Hydrolysis of maltose – by enzyme maltaseenzyme maltase

Chemical test for Chemical test for saccharides(sugars)saccharides(sugars)

Reducing SugarsReducing Sugars Heat the sugar solution with an equal Heat the sugar solution with an equal

volume of volume of blueblue benedict's solution for 2- benedict's solution for 2-3 minutes at about 903 minutes at about 90°C°C

A positive result is a A positive result is a brick redbrick red precipitate precipitate Benedicts solution contains Benedicts solution contains blueblue Cu Cu22+ +

ions, the sugar reduces this to the ions, the sugar reduces this to the insoluble insoluble brick redbrick red Cu+ compound Cu+ compound

CuCu22+ Cu++ Cu+Electron

From sugar

Non reducing sugar testNon reducing sugar test

Some sugars are Some sugars are non reducingnon reducing.. They do They do not reduce benedict's not reduce benedict's

solutionsolution One example is sucrose, it must be One example is sucrose, it must be

hydrolysedhydrolysed(broken-down by adding (broken-down by adding water) to form glucose and fructosewater) to form glucose and fructose

This can be done by heating with a This can be done by heating with a few drops of few drops of acidacid at 90 at 90°C for a few °C for a few minutes. Then minutes. Then neutralisingneutralising the the solution with an equal amount of solution with an equal amount of sodium hydroxide solutionsodium hydroxide solution

You will then get a positive result You will then get a positive result when repeating the benedict's testwhen repeating the benedict's test

SugarSugar Type of Type of saccharide?saccharide?

Result of Result of benedicts benedicts test for test for reducing reducing sugarsugar

Result of Result of non-non-reducing reducing sugar testsugar test

Reducing or Reducing or non-non-reducing reducing sugar?sugar?

lactoselactose

fructosfructosee

glucosglucosee

sucrossucrosee

maltosmaltosee

Quantitative Estimation of Quantitative Estimation of glucose concentration in a glucose concentration in a

solutionsolutionGlucose Glucose solution(%)solution(%)

Weight of Weight of precipitate precipitate (g)(g)

Light Light Transmission Transmission of filtrate (%)of filtrate (%)

00

0.010.01

0.050.05

0.10.1

0.50.5

11

Sugars homeworkSugars homework

a. Glyceraldehyde a. Glyceraldehyde – – C3 TrioseC3 Triose

Ribose Ribose C5 PentoseC5 Pentose

Glucose & Glucose & Fructose Fructose C6 HexoseC6 Hexose

b. Glucose is an b. Glucose is an aldose aldose sugar sugar H-C=O is on C H-C=O is on C11

c. c.

dd

e alpha glucose OH below the ringe alpha glucose OH below the ring

beta glucose OH above ringbeta glucose OH above ring

f alpha f alpha galactosegalactose

Polysaccharide- Structure & Polysaccharide- Structure & FunctionFunction

PolysaccharidesPolysaccharides are are polymerspolymers made up of made up of monosaccharide subunitsmonosaccharide subunits

The polymers can be many The polymers can be many thousand thousand monosaccharidesmonosaccharides – making macromolecules – making macromolecules

Most important are Most important are starch,glycogen & starch,glycogen & cellulosecellulose

All are polymers of All are polymers of glucoseglucose They are They are insolubleinsoluble in water and in water and do not do not

taste sweet.taste sweet.

StarchStarch Made up of a Made up of a

mixture of mixture of two two macromoleculesmacromolecules

Amylose (20%) Amylose (20%) andand amylopectin amylopectin (80%)(80%)

AmyloseAmylose

Amylose Amylose is formed by condensation is formed by condensation of a long chain of of a long chain of α glucoseα glucose using using 1α – 4 glycosidic bonds1α – 4 glycosidic bonds

Amylose Amylose α helixα helix

The 1The 1α – 4 glycosidic α – 4 glycosidic links in amylose mean links in amylose mean the glucose monomers the glucose monomers are at a slight angle to are at a slight angle to each othereach other

This causes a This causes a helixhelix to to formform

This is stabilised by This is stabilised by hydrogen bondshydrogen bonds

Amylopectin Amylopectin Branching chainsBranching chains of of α glucoseα glucose Branches about once every 25 Branches about once every 25

glucoseglucose Branches formed by 1-6 glycosidic Branches formed by 1-6 glycosidic

bondsbonds The branching structure gives many The branching structure gives many

“ends” to attach new glucose or to “ends” to attach new glucose or to remove it. So it is ideal for remove it. So it is ideal for storingstoring glucoseglucose

Starch – Role in living Starch – Role in living organismsorganisms

StarchStarch is a is a store of glucosestore of glucose in in plantsplants Plants cannot store sugars as this would Plants cannot store sugars as this would

increase the increase the osmotic potential (low osmotic potential (low water potential)water potential) of the cells,the solution of the cells,the solution inside the cells would be too inside the cells would be too concentrated.concentrated.

This would lead to ….This would lead to …. Starch is Starch is insolubleinsoluble and has and has no osmotic no osmotic

effecteffect

Starch GrainsStarch Grains

In plants starch is stored In plants starch is stored as as starch grainsstarch grains

These are most often These are most often found in found in chloroplastschloroplasts or in specialised plant or in specialised plant structures such as structures such as seedsseeds or or tuberstubers eg eg potatoespotatoes

The The helical shapehelical shape of of amylose means it can amylose means it can be be packed tightlypacked tightly

Chemical test for StarchChemical test for Starch Add Add iodine solution iodine solution to the materialto the material Iodine solution is orange brownIodine solution is orange brown A A blue black colourblue black colour is produced on contact is produced on contact

with starchwith starch This is because the iodine molecules fit into the This is because the iodine molecules fit into the

amylose helix giving the colouramylose helix giving the colour

GlycogenGlycogen Starch is not found in animal Starch is not found in animal

cellscells Glycogen is used to Glycogen is used to store store

glucoseglucose in in animal cellsanimal cells It is very similar to It is very similar to

amylopectin but more amylopectin but more branchedbranched

It branches every 8-10 It branches every 8-10 glucoses,again giving plenty glucoses,again giving plenty of of endsends to add extra glucose to add extra glucose

It forms It forms granulesgranules which can which can be seen in muscle & liver cellsbe seen in muscle & liver cells

CelluloseCellulose Cellulose makes up Cellulose makes up plant cell wallsplant cell walls It is a structural polysaccharideIt is a structural polysaccharide It is made up of It is made up of β glucoseβ glucose where OH is above where OH is above

the ringthe ring In order to form a glycosidic bond the other In order to form a glycosidic bond the other

glucose must be glucose must be upside downupside down.. The bond formed is a The bond formed is a β1-4 glycosidic bondβ1-4 glycosidic bond

Cellulose cross linksCellulose cross links Cellulose cannot form a helixCellulose cannot form a helix It exists in long chainsIt exists in long chains Chains lie side by side and hydrogen bonds Chains lie side by side and hydrogen bonds

form between themform between them These form between adjacent glucose These form between adjacent glucose

molecules and between the chains.molecules and between the chains.

This gives the cellulose molecule great mechanical strengthThis gives the cellulose molecule great mechanical strength They are insoluble,tough,durable and slightly elastic, ideal They are insoluble,tough,durable and slightly elastic, ideal

structural componentsstructural components 60-70 chains are strongly linked together to form bundles 60-70 chains are strongly linked together to form bundles

called microfibrilscalled microfibrils Microfibrils are held together in fibresMicrofibrils are held together in fibres Fibres make up the plant cell wallFibres make up the plant cell wall

Structure of celluloseStructure of cellulose

Cellulose fibres are laid Cellulose fibres are laid down in layers to form the down in layers to form the cell wallcell wall

Fibres are at right angles to Fibres are at right angles to increase strengthincrease strength

Other molecules help cross Other molecules help cross linkinglinking

Older cell walls are Older cell walls are reinforced with reinforced with ligninlignin

A glue like A glue like matrix(pectins)matrix(pectins) is laid is laid down in between the fibres down in between the fibres to increase strengthto increase strength

Similar to reinforced Similar to reinforced concreteconcrete

Cellulose – structure & Cellulose – structure & functionfunction

High tensile High tensile strengthstrength of cellulose fibres of cellulose fibres means they are difficult to break if pulled at means they are difficult to break if pulled at both endsboth ends

Allows the cell to withstand the pressure Allows the cell to withstand the pressure caused when water enters by osmosis.caused when water enters by osmosis.

Gives plant cells strength and rigidityGives plant cells strength and rigidity ProvidesProvides support support Despite strength they are Despite strength they are freely permeablefreely permeable Even though cellulose contains glucose it Even though cellulose contains glucose it

cannot be digested by most animals as they cannot be digested by most animals as they do not have the required enzymedo not have the required enzyme cellulase cellulase

Other structural Other structural polysaccharidespolysaccharides

ChitinChitin Exoskletons of Exoskletons of

arthropodsarthropods PeptidoglycanPeptidoglycan Cell wall of bacterial Cell wall of bacterial

cellscells

LipidsLipids

This group contains a wide range of This group contains a wide range of molecules ranging from molecules ranging from fats,oils,phospholipids,waxes & steroidsfats,oils,phospholipids,waxes & steroids

They all contain the elements C,H & OThey all contain the elements C,H & O Normally much less ONormally much less O The most widespread are The most widespread are

TRIGLYCERIDES also known as fats or TRIGLYCERIDES also known as fats or oilsoils

Triglyceride structureTriglyceride structure

Made up of 3 FATTY ACID moleculesMade up of 3 FATTY ACID molecules And 1 GLYCEROL moleculeAnd 1 GLYCEROL molecule

Fatty Acid structureFatty Acid structure

Stearic acid an example of a Stearic acid an example of a saturated fatty acidsaturated fatty acid.. All the carbon atoms in the tail are full,”saturated” All the carbon atoms in the tail are full,”saturated”

with hydrogenwith hydrogen

Can also be written as

CH3(CH2)16COOH

The COOH group is called a The COOH group is called a CARBOXYLIC ACIDCARBOXYLIC ACID group group

The long “tail” of the molecule is The long “tail” of the molecule is called a called a HYDROCARBON TAILHYDROCARBON TAIL

This hydrocarbon chain will not This hydrocarbon chain will not dissolve in water it is said to be dissolve in water it is said to be non-non-polarpolar or or hydrophobichydrophobic(water hating)(water hating)

The carboxylic acid The carboxylic acid group is group is polar polar or or hydrophilichydrophilic(water (water loving)loving)

Unsaturated Fatty AcidsUnsaturated Fatty Acids

These fatty acids These fatty acids contain a double bondcontain a double bond

It causes a “kink” in It causes a “kink” in the tailthe tail

These fatty acids melt These fatty acids melt more easilymore easily

One double bond is One double bond is monounsaturatedmonounsaturated

More than one are More than one are called polyunsaturatedcalled polyunsaturated

Glycerol structureGlycerol structure

Glycerol is a Glycerol is a type of alcohol type of alcohol with 3 alcohol with 3 alcohol groups.groups.

Forming a Forming a triglyceridetriglyceride

When glycerol combines with a fatty acid it forms a When glycerol combines with a fatty acid it forms a glycerideglyceride

When it combines with 3 fatty acids it is a triglycerideWhen it combines with 3 fatty acids it is a triglyceride They combine in a condensation reaction, losing waterThey combine in a condensation reaction, losing water Forming an ester linkForming an ester link

PropertiesProperties

Triglycerides are Triglycerides are insolubleinsoluble in water, they in water, they are are non-polarnon-polar molecules molecules

The more The more unsaturated fatty acids unsaturated fatty acids the the lower the melting point lower the melting point making these making these oils at room temperature, normally found oils at room temperature, normally found in plantsin plants

Animal fats have a Animal fats have a higher melting point higher melting point and are generally solid at room and are generally solid at room temperature due to saturated fatty acidstemperature due to saturated fatty acids

Roles of Roles of triglyceridestriglycerides

ENERGY RESERVES- high ENERGY RESERVES- high number of C-H bonds so number of C-H bonds so much more energy much more energy content than content than carbohydrate-so you need carbohydrate-so you need to store less to get the to store less to get the same energysame energy

In humans stored around In humans stored around organs and under the skinorgans and under the skin

Stored in adipose tissueStored in adipose tissue

Under the skin it is Under the skin it is also also INSULATIONINSULATION eg blubber in sea eg blubber in sea mammalsmammals

It can also produce It can also produce metabolic watermetabolic water when used in when used in respiration by respiration by desert animals such desert animals such as camelsas camels

Insoluble: Insoluble: so no so no osmotic effectosmotic effect

PhospholipidPhospholipidss

In this molecule In this molecule the glycerol has the glycerol has two fatty acids two fatty acids attachedattached

On the 3On the 3rdrd carbon carbon is a phosphate is a phosphate groupgroup

Phospholipid examplesPhospholipid examples

Phospholipid properties Phospholipid properties and rolesand roles

These molecules have a These molecules have a hydrophobic tail and hydrophobic tail and hydrophilic headhydrophilic head

They form the membranes They form the membranes of living cellsof living cells

Cholesterol Cholesterol

Not formed from fatty Not formed from fatty acids and glycerolacids and glycerol

4 carbon based rings4 carbon based rings Small hydrophobic Small hydrophobic

moleculemolecule Found between Found between

phospholipid tails in phospholipid tails in membranesmembranes

Controls membrane Controls membrane fluidity and mechanical fluidity and mechanical strengthstrength

Excess Excess cholesterolcholesterol

Many cells make Many cells make cholesterol from cholesterol from saturated fatssaturated fats

Especially liver cellsEspecially liver cells Excess can be Excess can be

deposited in artery deposited in artery wallswalls

Causing atherosclerosisCausing atherosclerosis

Excess Excess cholesterol cholesterol is removed is removed in bilein bile

It can form It can form gallstones gallstones in the gall in the gall bladderbladder

Steroid hormonesSteroid hormones These are made from cholesterol and include:These are made from cholesterol and include:

Chemical test for LipidsChemical test for Lipids

Emulsion testEmulsion test Add ethanol to the suspect Add ethanol to the suspect

material and mix well (any material and mix well (any fat will dissolve in the fat will dissolve in the alcohol)alcohol)

Filter off the ethanolFilter off the ethanol pour the ethanol into waterpour the ethanol into water A milky emulsion will form A milky emulsion will form

if fat was present(fat can if fat was present(fat can no longer dissolve and no longer dissolve and forms small dropletsforms small droplets

Proteins(Polypeptides)Proteins(Polypeptides)

Proteins make up more than 50% of Proteins make up more than 50% of the dry mass of cellsthe dry mass of cells

They have many important functions They have many important functions All proteins are made up of All proteins are made up of amino amino

acidsacids Functions of proteinsFunctions of proteins

Proteins in living organisms

globular

fibrous

enzymes

transport

membrane

blood

channel protein

active transport

complexglycoprotei

n

contractile

structural

blood

collagen

elastin

keratin Fibrinogen (fibrin)

Actin/myosin (muscles)

Respiration/ photosynthesis

Albumin/ globulin

antibodies

hormones

haemoglobin

intracellular (metabolic)

Extracellular (digestive)

Proteins in living organisms

Amino Acid StructureAmino Acid Structure NHNH22 is the a is the a amine or amine or

amino groupamino group COOHCOOH is the is the carboxylic carboxylic

acidacid group group The The R groupR group or amino or amino

acid acid side chainside chain varies. varies. There are There are 2020 different R different R

groups found in nature groups found in nature so giving 20 different so giving 20 different naturally occuring amino naturally occuring amino acidsacids

The 20 The 20 naturally naturally occurring occurring amino amino acids R acids R groupsgroups

Amino AcidsAmino Acids

The Peptide BondThe Peptide Bond Amino acids are joined together by a Amino acids are joined together by a

peptide bondpeptide bond Two amino acids joined form a dipeptideTwo amino acids joined form a dipeptide

Peptide bond formationPeptide bond formation

Polypeptide formationPolypeptide formation Adding more Adding more

amino acids to the amino acids to the chain forms a chain forms a polypeptide polypeptide

In cells this occurs In cells this occurs in in ribosomes ribosomes

A protein molecule A protein molecule may contain many may contain many hundred AAs and hundred AAs and sometimes more sometimes more than one than one polypeptide chainpolypeptide chain

Protein – Primary Protein – Primary structurestructure

The sequence of the The sequence of the amino acids in the amino acids in the polypeptide is known as polypeptide is known as its primary structureits primary structure

A protein of several A protein of several hundred amino acids hundred amino acids has a huge number of has a huge number of possible primary possible primary structuresstructures

A change in A change in oneone of the of the AAs can completely AAs can completely alter the properties of alter the properties of the proteinthe protein

Protein- Secondary Protein- Secondary StructureStructure

This is when This is when partsparts of the of the polypeptide chain polypeptide chain becomes becomes twisted twisted or foldedor folded

There are There are 22 main main types of 2types of 2° ° structure:structure:

helixhelix pleated sheetpleated sheet

Polypeptide Polypeptide α helixα helix

Proteins form this Proteins form this stable helix due to stable helix due to hydrogen bondinghydrogen bonding

This takes place This takes place between –C=O of between –C=O of one A.A one A.A

And the –N-H of And the –N-H of the A.A 4 places the A.A 4 places aheadahead

Polypeptide - Polypeptide - β Pleated β Pleated SheetSheet

This looser, straighter shape is also formed This looser, straighter shape is also formed by H bonds.by H bonds.

This time between –C=O and –N-H of This time between –C=O and –N-H of adjacent chainsadjacent chains

Proteins may contain both of these Proteins may contain both of these secondary structuressecondary structures

They are easily disrupted by heat & changes They are easily disrupted by heat & changes in pHin pH

Biological molecules chemical Biological molecules chemical teststests

Reducing SugarsReducing Sugars Heat the sugar solution with an equal volume of Heat the sugar solution with an equal volume of blueblue benedict's solution benedict's solution

for 2-3 minutes at about 90for 2-3 minutes at about 90°C°C A positive result is a A positive result is a brick redbrick red precipitate precipitate Non reducing sugar (sucrose)Non reducing sugar (sucrose) Collect some filtrate from the reducing sugar testCollect some filtrate from the reducing sugar test Add a few drops of acid and heat in a water bath for a few minutesAdd a few drops of acid and heat in a water bath for a few minutes Neutralise with an equal amount of sodium hydroxide solutionNeutralise with an equal amount of sodium hydroxide solution Repeat the benedicts test, a Repeat the benedicts test, a brick redbrick red ppt is a positive result ppt is a positive result StarchStarch Add Add orange brownorange brown iodine solutioniodine solution to the material to the material A A blue black colourblue black colour is produced on contact with starch is produced on contact with starch ProteinProtein Biuret reagent is made by combining equal amounts of Sodium Biuret reagent is made by combining equal amounts of Sodium

Hydroxide and Copper SulphateHydroxide and Copper Sulphate Add biuret reagent to the suspect food or add some dilute sodium Add biuret reagent to the suspect food or add some dilute sodium

hydroxide solution and mix followed by a little dilute copper sulphate hydroxide solution and mix followed by a little dilute copper sulphate solution.solution.

The copper ions interact with the amino groups in the protein to give The copper ions interact with the amino groups in the protein to give PURPLEPURPLE colour for a colour for a positivepositive result result

If the solution stays If the solution stays BLUEBLUE this is a this is a negative negative resultresult

Food TestingFood Testing

StarchStarch Add Add orange brownorange brown iodine solutioniodine solution to the material to the material A A blue black colourblue black colour is produced on contact with starch is produced on contact with starch

ProteinProtein Biuret reagent is made by combining equal amounts of Sodium Biuret reagent is made by combining equal amounts of Sodium

Hydroxide and Copper SulphateHydroxide and Copper Sulphate Add biuret reagent to the suspect food or add some dilute Add biuret reagent to the suspect food or add some dilute

sodium hydroxide solution and mix followed by a little dilute sodium hydroxide solution and mix followed by a little dilute copper sulphate solution.copper sulphate solution.

The copper ions interact with the amino groups in the protein to The copper ions interact with the amino groups in the protein to give give PURPLEPURPLE colour for a colour for a positivepositive result result

If the solution stays If the solution stays BLUEBLUE this is a this is a negative negative resultresult