Izzy- Biology- topic1 biological molecules-molecules of life


monomers and polymers

carbohydrates, proteins and mucleic acids are polymers. 

POLYMER: A large complex molecules composed of long chains of monomers joined togther.

MONOMER: Small basic molecular units that can form a polymer.

Examples of monomers include monosaccharides, amino acids and nucleotides.


Most biological polymers are fromed from their monomers by a condensation reaction. A condensation reaction forms a chemical bond between monomers releasing a molecule of water.


Biologocal polymers can be broken down in to monomers by hydrolosis reactions. A hydrolosis reactiom breaks the chemical bond betwween monomers using a water molecule. The opposite of a condensation reaction.

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sugar is a general term for monosaccharides and disaccharides. Monosaccharides are the simplest form of sugars and are the building blocks of carbohydrates.


All carbohydrates contain the elements C,H,O. The monomers that carbohydrates are made from are called mobosaccharides ( glucose, galactose and fructose)

Glucose is a hexose sugar. there are two types alpha and beta. they are isomers.( molecules witht the same molecular formula but with atoms connected in different ways)


They are formed when two monosaccharides join together. T hey are joined by a condensation reaction. A glycosidic bond forms between the monosaccharides as a molecule of water is released.

glucose+glucose=maltose glucose+galactose= lactose glucose+fructose=sucrose

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Test for sugars

The Benedicts test for sugars 


Add Benedicts reagent (blue) to a sample and heat in a water bath. If the test is positive it iwll form a coloured precipitate.(brick red)


If the test for the reducing sugar test is negaive there could still be a sugar present. To test for non-reducing sugars you have to break the smaple down inot monosaccharides by adding hydrocholoric acid and heating in a water bath. Then neutralise by addind sodium hydrogencarbonte. Then carry out the Benedicts test.

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A polysaccharide is formed when more than two monosaccharides jion together.

STARCH- Cells get their energy from glucose.starch is a mixture of two polysaccharides amylose and amylopectin. Amylose is a coiled chain of alpha glucose. Its structure makes it compact and good for storage as it can fit more into a small space. Amylopectin is a long branched chain of alpha glucose. Its side branches allow the enzymes to get at the glycosidic bonds quickly so glucose can be relseaed quicker. Starch is insoluble in water and doesnt affect the water potential so it isnt sweet.

GLYCOGEN- Animals get energy from glucose in the form of glycogen. It is similar to amylopectin but has more side branches so energy is released quicker.

CELLULOSE-  Cellulose is made from long unbranched chains of beta glucose. when they bond they form long straight cellulose chains. The cellulose chains are linked together by hydrogen bonds to form long fibres called microfibrils. This is why cellulose makes a good cell wall. 

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Test for starch

If you want to test for starch in a sample you will need to do the iodine test.

Add iodine dissolved in potassium iodide soution tp the test sample.

If the test is positive the solution will change from a bown-orange colour to a blue-black colour.

If the test is negative there will be no colour change.

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