Monomers & Polymers: Carbohydrates

Monomer

small soluble molecule from which larger molecules are formed

Polymer

Molecules made from many similar monomers joined together.

Monomer of carbohydrate

Monosaccharide

Polymer of carbohydrate

Polysaccharide

Monomer of proteins

Amino acid

Polymer of proteins

Polypeptide

Monomer of DNA

Nucleotide

Polymer of DNA

Polynucleotide

Lipids are not polymers. Why?

They are not made up of similar repeating subunits, this have both fatty acid and glycerol molecule

Elements that are in carbohydrates

Carbon hydrogen, oxygen.

Types of carbohydrates

Monosaccharides

Disaccharides

Polysaccharides

Condensation reaction

Joins two molecules together by the formation of a chemical bond and it involves the elimination of a water molecule. Eg. monomers joining together

Glycosidic bond

Bond formed between monosaccharides and in condensation reaction

Hydrolysis reaction

Breaks a chemical bond between two molecules and it involves the use of a water molecule. Eg polymers breaking down

Monosaccharides

monomers from which larger carbohydrates are made

Monosaccharides

Glucose, fructose, galactose

General formula for monosaccharides

C6H12O6

Disaccharides

two monosaccharides joined together by a glycosidic bond which forms during a condensation reaction.

Disaccharides

Maltose, sucrose, lactose

General formula for disaccharides

C12H22O11 + H20

Formation of disaccharides

Maltose → glucose + glucose

Lactose → glucose + galactose

Sucrose → glucose + fructose

Isomers of glucose

Alpha- glucose and beta-glucose

Isomer

An isomer of a molecule has the same chemical formula, but a different structural formula

Alpha- glucose

Beta glucose

Difference between the two glucose isomers.

The position of the hydrogen (H) and hydroxyl (OH) groups on carbon 1 are INVERTED

Polysaccharides

formed by the condensation of many repeating monosaccharides.

Polysaccharides

Cellulose : beta-glucose

Starch: alpha-glucose

glycogen: alpha-glucose

Starch + glycogen

Made from alpha-glucose

Found in plants

Insoluble

Has both 1,4 and 1,6 glycosidic bond

Cellulose

Made from beta-glucose

Found in plant’s cell wall

Insoluble

Has 1,4 glycosidic bond

Difference between the appearance of a polymer of alpha-glucose ( glycogen or starch) and a polymer of beta- glucose (cellulose)

In cellulose, the monomers face in alternate directions rather them all in the same way like in starch or glycogen. This is because in beta-glucose, the position of the hydrogen and hydroxyl groups on carbon atom 1 are inverted

Structure of starch and it’s functions

Coiled into a helix so it is compact and can fit into a small space

Insoluble so it does not affect water potential OR so it does not affect osmosis and not easily lost from cell

Branches which gives a larger surface area so it is more rapidly hydrolysed and glucose can e released more rapidly for respiration for energy release

Large molecule so it does not diffuse out of cell membrane and out of cells

Structure of glycogen and its functions

Coiled into a helix so it is compact and can fit into a small space

Insoluble so it does not affect water potential OR so it does not affect osmosis and not easily lost from cell

Branches which gives a larger surface area so it is more rapidly hydrolysed and glucose can e released more rapidly for respiration for energy release

Polymer of alpha-glucose so it is rapidly hydrolysed

Structure of cellulose and it’s function

Long, straight and unbranched chains of beta glucose;

Linked together by many hydrogen bonds to for micro fibrils;

Provides strength and rigidity to plant cell wall

Biochemical test for starch

Add iodine solution (solid iodine + potassium iodide solution)

A colour change from orange to black indicates the presence of starch

Biochemical test for reducing sugars

Add Benedict’s solution to food sample

Heat to 95° C (don’t boil)

A colour change from blue to orange/red indicates the presence of reducing sugars

Benedict’s test

The difference in colours (blue - green - yellow - orange - red) means it is a semi-quantitative test as it can be used to estimate the concentration of reducing sugar in a sample.

To get a quantitative measure:

Filter the liquid and dry the precipitate in the sample

Find the mass

The higher the mass of the precipitate, the more reducing sauger is present.

Using a colorimeter:

A higher absorbance has a higher sugar concentration

Biochemical test for non-reducing sugar

Do Benedict’s test and the sample stays blue

Boil a fresh sample with acid to hydrolyse the glycosidic bond

Neutralise with alkali- sodium hydrogen carbonate

Add Benedict’s solution and heat to 95° C

A colour change from blue to orange/red indicates the presence of a non-reducing sugar.

Reducing sugars

Glucose

Fructose

Galactose

Lactose

Maltose

Non-reducing sugars

Sucrose