CarbohydrateCarbohydratess

What are carbohydrates?What are carbohydrates?

Starter:Starter:Write down as many things as you can Write down as many things as you can remember about carbohydrates…remember about carbohydrates…

… … or glucose in particularor glucose in particular

What are they?What are they?

Organic compounds which Organic compounds which comprise of only C, H and Ocomprise of only C, H and O

CarboCarbo--HydrHydr--ateate

Types of CarbohydrateTypes of Carbohydrate

MonosaccharidesMonosaccharides

DisaccharidesDisaccharides

PolysaccharidesPolysaccharides

MonosaccharidesMonosaccharides

Simplest – ‘Single sugars’Simplest – ‘Single sugars’ Same no. of C as O atomsSame no. of C as O atoms

e.g. Glucose is Ce.g. Glucose is C66HH1212OO66

Have the general formula (CHHave the general formula (CH22O)O)nn

Where n is any number between 3 and 7Where n is any number between 3 and 7

White crystalline solidsWhite crystalline solids Dissolve in water to form sweet tasting Dissolve in water to form sweet tasting

solutionssolutions

The structure of glucoseThe structure of glucose

αα-glucose-glucose

You only need to be able to draw α-glucose in its simplified form….

ββ-glucose -glucose

The structure of glucoseThe structure of glucose

• α-glucose and β-glucose are ISOMERS

Monosaccharides form Monosaccharides form DisaccharidesDisaccharides

+

H2O

Maltose

The bond formed is a The bond formed is a glycosidicglycosidic bond bond

A A condensation reaction condensation reaction occurs to join occurs to join the 2 monosaccharidesthe 2 monosaccharides

Monosaccharides form Disaccharides

• α 1-4 glycosidic bonds

Disaccharides hydrolyse to form Disaccharides hydrolyse to form MonosaccharidesMonosaccharides

α-glucose α-glucose

H2O

Disaccharides form Disaccharides form PolysaccharidesPolysaccharides

StarchStarch

StarchStarch The The αα-helical structure of starch makes it -helical structure of starch makes it

good for good for storagestorage (it’s compact!) (it’s compact!) Starch is Starch is insolubleinsoluble due to its structure due to its structure It is therefore the main It is therefore the main plant storageplant storage

sugarsugar

CelluloseCellulose Polymer of Polymer of ββ-glucose-glucose Each monomer is Each monomer is

inverted.inverted. Has consequences forHas consequences for

its properties its properties

CelluloseCellulose Forms chains which run parallel with Forms chains which run parallel with

hydrogen bonds between the chains to hydrogen bonds between the chains to form form microfibrilsmicrofibrils

Microfibrils are strongMicrofibrils are strong Being fibrous, cellulose is structurally Being fibrous, cellulose is structurally

important in important in plant cell wallsplant cell walls

Glucose is not the only Glucose is not the only monosaccharide...monosaccharide...

Fructose:Fructose:

Glucose and fructosecombine to form sucrose (a disaccharide)

Glucose is not the only Glucose is not the only monosaccharide...monosaccharide...

GalactoseGalactose

Galactose Glucose

Glucose and galactose combine to form Lactose

SummarySummary

αα-glucose + -glucose + αα-glucose = -glucose = maltosemaltose The polymer of The polymer of αα-glucose is -glucose is starchstarch The polymer of The polymer of ββ-glucose is -glucose is cellulosecellulose Glucose + fructose = Glucose + fructose = sucrosesucrose Glucose + galactose = Glucose + galactose = lactoselactose

Biochemical Test for Biochemical Test for a Monosaccharidea Monosaccharide

All monosaccharides and All monosaccharides and somesome disaccharides are disaccharides are Reducing SugarsReducing Sugars

i.e. They readily reduce other i.e. They readily reduce other chemicals chemicals when in solutionwhen in solution

We test for reducing sugars using the We test for reducing sugars using the

Benedict’s TestBenedict’s Test

Benedicts TestBenedicts Test

2cm³ of food sample (in liquid form)2cm³ of food sample (in liquid form) 2cm³ of Benedict’s Reagent 2cm³ of Benedict’s Reagent Heat mixture in gentle boiling water bath Heat mixture in gentle boiling water bath

for 5minsfor 5minsConc. of reducing sugarConc. of reducing sugar Colour of solution & Colour of solution &

precipitateprecipitate

NoneNone Stays blueStays blue

Very LowVery Low GreenGreen

LowLow YellowYellow

MediumMedium Brown/orangeBrown/orange

HighHigh Brick redBrick red

In order to detect a reducing sugar, it In order to detect a reducing sugar, it mustmust first be first be hydrolysedhydrolysed into its monosaccharide into its monosaccharide components:components: First test with Benedict’s reagentFirst test with Benedict’s reagent If no colour change:If no colour change:

Add 2cm³ of food sample to 2cm³ of dilute HClAdd 2cm³ of food sample to 2cm³ of dilute HCl Place in gently boiling water bath for 5 minsPlace in gently boiling water bath for 5 mins Slowly add some sodium hydrogen carbonate Slowly add some sodium hydrogen carbonate

solution until neutralized solution until neutralized Re-test using Benedict’s reagentRe-test using Benedict’s reagent